The Structure of the Genetic Material

The Structure of the Genetic Material

10.1 SCIENTIFIC THINKING: Experiments showed that DNA is the genetic material
Early in the 20th century, the molecular basis for inheritance was a mystery. Biologists did know that genes were located on chromosomes. But it was unknown if the genetic material was proteins or DNA. Student Misconceptions and Concerns • Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. Teaching Tips • A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).

Biologists finally established the role of DNA in heredity through experiments with bacteria and the viruses that infect them. This breakthrough ushered in the field of molecular biology, the study of heredity at the molecular level. Student Misconceptions and Concerns • Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. Teaching Tips • A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).

In 1928, Frederick Griffith was surprised to find that when he killed pathogenic bacteria, then mixed the bacterial remains with living harmless bacteria, some living bacterial cells became pathogenic. All of the descendants of the transformed bacteria inherited the newly acquired ability to cause disease. Student Misconceptions and Concerns • Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. Teaching Tips • A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).

In 1952, Alfred Hershey and Martha Chase used bacteriophages to show that DNA is the genetic material of T2, a virus that infects the bacterium Escherichia coli (E. coli). Bacteriophages (or phages for short) are viruses that infect bacterial cells. Phages were labeled with radioactive sulfur to detect proteins or radioactive phosphorus to detect DNA. Bacteria were infected with either type of labeled phage to determine which substance was injected into cells and which remained outside the infected cell. Student Misconceptions and Concerns • Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. Teaching Tips • A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).

The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus- labeled DNA was detected inside cells. Cells with phosphorus-labeled DNA produced new bacteriophages with radioactivity in DNA but not in protein. Student Misconceptions and Concerns • Understanding bacteriophage replication can be difficult for students with limited knowledge of cell biology or genetics. Therefore, understanding the methods, results, and significance of the Hershey and Chase experiments is even more problematic. Considerable time and attention to these details will be required for many of your students. • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. Teaching Tips • A phage functions like a needle and syringe, injecting a drug. The needle and syringe are analogous to the protein components of the phage. The drug to be injected is analogous to the phage DNA. • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff).

Figure 10.1a-0 Head DNA Tail Tail fiber Figure 10.1a-0 Phage T2

The radioactivity is in the liquid. Bacterium
Figure 10.1b-0 Phage Radioactive protein Empty protein shell The radioactivity is in the liquid. Bacterium Phage DNA DNA Centrifuge Pellet Batch 1: Radioactive protein labeled in yellow Figure 10.1b-0 The Hershey-Chase experiment Radioactive DNA Centrifuge The radioactivity is in the pellet. Pellet Batch 2: Radioactive DNA labeled in green

10.2 DNA and RNA are polymers of nucleotides
DNA and RNA are nucleic acids consisting of long chains (polymers) of chemical units (monomers) called nucleotides. One of the two strands of DNA is a DNA polynucleotide, a nucleotide polymer (chain). A nucleotide is composed of a nitrogenous base, five-carbon sugar, and phosphate group. The nucleotides are joined to one another by a sugar- phosphate backbone. The Structure of the Genetic Material Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). • Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.

Sugar-phosphate backbone
Figure 10.2a-0 A T C G T A Sugar-phosphate backbone C G A T Phosphate group G C A A G Nitrogenous base Nitrogenous base (can be A, G, C, or T) Covalent bond joining nucleotides A T Sugar G C T A C C T A C G T A DNA nucleotide Thymine (T) A DNA double helix T T Phosphate group Figure 10.2a-0 The structure of a DNA polynucleotide G G Sugar (deoxyribose) DNA nucleotide G G Two representations of a DNA polynucleotide

Each type of DNA nucleotide has a different nitrogen-containing base: adenine (A), cytosine (C), thymine (T), and guanine (G). The Structure of the Genetic Material Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). • Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.

Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines
Figure 10.2b-0 Thymine (T) Cytosine (C) Adenine (A) Guanine (G) Pyrimidines Purines Figure 10.2b-0 The nitrogenous bases of DNA

The full name for DNA is deoxyribonucleic acid, with nucleic referring to DNA’s location in the nuclei of eukaryotic cells. RNA (ribonucleic acid) is unlike DNA in that it uses the sugar ribose (instead of deoxyribose in DNA) and has a nitrogenous base uracil (U) instead of thymine. The Structure of the Genetic Material Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). • Consider comparing DNA, RNA, and proteins to a train (polymer). DNA and RNA are like a train of various lengths and combinations of four types of train cars (monomers). Proteins are also “trains” of various lengths but made of a combination of 20 types of train cars.

Nitrogenous base (can be A, G, C, or U)
Figure 10.2c Nitrogenous base (can be A, G, C, or U) Phosphate group Uracil (U) Figure 10.2c An RNA nucleotide Sugar (ribose)

10.3 DNA is a double-stranded helix
After the 1952 Hershey-Chase experiment convinced most biologists that DNA was the material that stored genetic information, a race was on to determine how the structure of this molecule could account for its role in heredity. Researchers focused on discovering the three- dimensional shape of DNA. Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). Active Lecture Tips • The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to pair up with someone nearby to explain what the parts of the ladder represent. Answer: The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

American James D. Watson journeyed to Cambridge University in England, where the more senior Francis Crick was studying protein structure with a technique called X-ray crystallography. While visiting the laboratory of Maurice Wilkins at King’s College in London, Watson saw an X-ray image of DNA produced by Wilkins’s colleague, Rosalind Franklin. Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). Active Lecture Tips • The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to pair up with someone nearby to explain what the parts of the ladder represent. Answer: The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Figure 10.3a-0 Figure 10.3a-0 Rosalind Franklin and her X-ray image of DNA

Watson deduced the basic shape of DNA to be a helix (spiral) with a uniform diameter and the nitrogenous bases located above one another like a stack of dinner plates. The thickness of the helix suggested that it was made up of two polynucleotide strands. Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). Active Lecture Tips • The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to pair up with someone nearby to explain what the parts of the ladder represent. Answer: The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Watson and Crick realized that DNA consisted of two polynucleotide strands wrapped into a double helix. The sugar-phosphate backbone is on the outside. The nitrogenous bases are perpendicular to the backbone in the interior. Specific pairs of bases give the helix a uniform shape. A pairs with T, forming two hydrogen bonds, and G pairs with C, forming three hydrogen bonds. Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). Active Lecture Tips • The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to pair up with someone nearby to explain what the parts of the ladder represent. Answer: The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Figure 10.3b Figure 10.3b Watson and Crick in 1953 with their model of the DNA double helix

Partial chemical structure Computer model
Figure 10.3d-0 C G C G Hydrogen bond G C G C G C Base pair T A A T T A C G A T A T T A C G G C C G C G Figure 10.3d-0 Three representations of DNA A T A T T A Ribbon model Partial chemical structure Computer model

In 1962, the Nobel Prize was awarded to James D. Watson, Francis Crick, and Maurice Wilkins. Rosalind Franklin probably would have received the prize as well but for her death from cancer in 1958. Nobel Prizes are never awarded posthumously. The Watson-Crick model gave new meaning to the words genes and chromosomes. The genetic information in a chromosome is encoded in the nucleotide sequence of DNA. Student Misconceptions and Concerns • If your class has not yet studied Chapter 3, consider assigning Module 3.15 on Nucleic Acids before addressing the contents of Chapter 10. • Students often confuse the terms nucleic acids, nucleotides, and bases. It helps to note the hierarchy of relationships: nucleic acids consist of long chains of nucleotides (polynucleotides), while nucleotides include nitrogenous bases. Teaching Tips • The descriptions of the discovery of DNA’s structure are a good time to point out that science is a collaborative effort. Watson, Crick, and Wilkins earned Nobel Prizes due to their historic conclusions based upon the work of many others (including Franklin, Griffith, Hershey, Chase, and Chargaff). Active Lecture Tips • The authors note that the structure of DNA is analogous to a twisted rope ladder. In class, challenge your students to pair up with someone nearby to explain what the parts of the ladder represent. Answer: The wooden rungs represent pairs of nitrogenous bases joined by hydrogen bonds. Each rope represents a sugar-phosphate backbone.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

DNA Replication

10.4 DNA replication depends on specific base pairing
DNA replication follows a semiconservative model. The two DNA strands separate. Each strand then becomes a template for the assembly of a complementary strand from a supply of free nucleotides. Each new DNA helix has one old strand with one new strand. Student Misconceptions and Concerns • The authors note that although the general process of semiconservative DNA replication is relatively simple, it is actually quite complex. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips • The semiconservative model of DNA replication is like making a photo from a negative and then a new negative from the photo. In each new negative and photo pair, the new item was made from an old item. Active Lecture Tips • Demonstrate the complementary base pairing within DNA. Present students with the base sequence to one side of a DNA molecule and have them work in pairs at their seats to quickly determine the sequence of the complementary strand. For some students, these sorts of quick practice are necessary to reinforce a concept and break up a lecture.  See the Activity I’m Not Sure I Liked James Watson: Using a Video to Tell the Most Exciting Discovery in Biology on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

A parental molecule of DNA The parental strands separate
Figure 10.4a-3 A T A T A T A T A T C G C G G C G C G C G C G C C G C G C A A T A T A T A T T A T A T A Free nucleotides T A A parental molecule of DNA The parental strands separate and serve as templates Two identical daughter molecules of DNA are formed Figure 10.4a-3 A template model for DNA replication (step 3)

Daughter DNA molecules
Figure 10.4b A T G C A T Parental DNA molecule A T T A C G G C T Daughter strand Parental strand A C C G G G C T G C T T C A A G A A Figure 10.4b The untwisting and replication of DNA G T C C A G T A T A T A G Daughter DNA molecules T C

10.5 DNA replication proceeds in two directions at many sites simultaneously
Replication of a DNA molecule begins at particular sites called origins of replication, short stretches of DNA having a specific sequence of nucleotides. Proteins that initiate DNA replication attach to the DNA at the origin of replication and separate the two strands of the double helix. Replication then proceeds in both directions, creating replication “bubbles.” Student Misconceptions and Concerns • The authors note that although the general process of semiconservative DNA replication is relatively simple, it is actually quite complex. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips • To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. • There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one uncorrected error in every 1 billion words.

DNA replication occurs in the 5 to 3 direction. Replication is continuous on the 3 to 5 template. DNA polymerases add nucleotides only to the 3 end of the strand, never to the 5 end. Replication is discontinuous on the 5 to 3 template, forming short Okazaki fragments. An enzyme, called DNA ligase, links (or ligates) the pieces together into a single DNA strand. Student Misconceptions and Concerns • The authors note that although the general process of semiconservative DNA replication is relatively simple, it is actually quite complex. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips • To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. • There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one uncorrected error in every 1 billion words.

5′ end 3′ end P HO A T P P C G P P G C P P T A OH P 3′ end 5′ end 5′
Figure 10.5b 5′ end 3′ end P HO 5′ 2′ 4′ A T 3′ 3′ 1′ 1′ 4′ 2′ P 5′ P C G P P G C P Figure 10.5b The opposite orientations of DNA strands P T A OH P 3′ end 5′ end

DNA polymerase molecule
Figure 10.5c 3′ DNA polymerase molecule This daughter strand is synthesized continuously 5′ Parental DNA 5′ 3′ Replication fork This daughter strand is synthesized in pieces 3′ 5′ 5′ Figure 10.5c How daughter DNA strands are synthesized 3′ DNA ligase Overall direction of replication

DNA polymerases and DNA ligase also repair DNA damaged by harmful radiation and toxic chemicals. DNA replication ensures that all the somatic cells in a multicellular organism carry the same genetic information. Student Misconceptions and Concerns • The authors note that although the general process of semiconservative DNA replication is relatively simple, it is actually quite complex. The DNA molecule is unwound, each strand is copied simultaneously, the correct bases are inserted, and the product is proofread and corrected. Before discussing these details, be sure that your students understand the overall process, what is accomplished, and why each step is important. Teaching Tips • To explain the adaptive advantage of multiple replication sites over a single site of replication, ask the students to imagine copying, by hand, the first ten chapters of your biology textbook. The task would certainly go faster if ten students each copied a different chapter. • There are about 500,000 words in the Biology: Concepts & Connections textbook. The accuracy of DNA replication would be like copying every word in this textbook by hand 2,000 times and writing just one word incorrectly, making one uncorrected error in every 1 billion words.

The Flow of Genetic Information from DNA to RNA to Protein

10.6 Genes control phenotypic traits through the expression of proteins
DNA specifies traits by dictating protein synthesis. Proteins are the links between genotype and phenotype. The molecular chain of command is from DNA in the nucleus to RNA and RNA in the cytoplasm to protein. Student Misconceptions and Concerns • Consider placing the basic content from Figure 10.6A on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to evaluate the validity of this statement. • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Transcription is the synthesis of RNA under the direction of DNA. Translation is the synthesis of proteins under the direction of RNA. Student Misconceptions and Concerns • Consider placing the basic content from Figure 10.6A on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to evaluate the validity of this statement. • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

DNA Transcription RNA NUCLEUS CYTOPLASM Translation Protein
Figure 10.6a-3 DNA Transcription RNA NUCLEUS CYTOPLASM Translation Figure 10.6a-3 The flow of genetic information in a eukaryotic cell (step 3) Protein

Genes provide the instructions for making specific proteins. The initial one gene–one enzyme hypothesis was based on studies of inherited metabolic diseases. The one gene–one enzyme hypothesis was expanded to include all proteins. Student Misconceptions and Concerns • Consider placing the basic content from Figure 10.6A on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to evaluate the validity of this statement. • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Most recently, the one gene–one polypeptide hypothesis recognizes that some proteins are composed of multiple polypeptides. Even this description is not entirely accurate, in that the RNA transcribed from some genes is not translated but nonetheless has important functions. In addition, many eukaryotic genes code for a set of polypeptides (rather than just one) by a process called alternative splicing. Student Misconceptions and Concerns • Consider placing the basic content from Figure 10.6A on the board, noting the sequence, products, and locations of transcription and translation in eukaryotic cells. This reminder can create a quick concept check for students as they learn additional detail. • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • It has been said that everything about an organism is an interaction between the genome and the environment. You might wish to challenge your students to evaluate the validity of this statement. • The information in DNA is used to direct the production of RNA, which in turn directs the production of proteins. However, in Chapter 3, four different types of biological molecules were noted as significant components of life. Students who think this through might wonder, and you could point out, that DNA does not directly control the production of carbohydrates and lipids. So how does DNA exert its influence over the synthesis of these two chemical groups? The answer is largely by way of enzymes, proteins with the ability to promote the production of carbohydrates and lipids. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.7 Genetic information written in codons is translated into amino acid sequences
The sequence of nucleotides in DNA provides a code for constructing a protein. Protein construction requires a conversion of a nucleotide sequence to an amino acid sequence. Transcription rewrites the DNA code into RNA, using the same nucleotide “language.” Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • The transcription of DNA into RNA is like a reporter who transcribes a political speech. In both situations, the language remains the same, although in the case of the reporter, it changes its form from spoken to written language. • The sequential information in DNA and RNA is analogous to the sequential information in the letters of a sentence. This analogy is also helpful when explaining the impact of insertion or deletion mutations that cause a shift in the reading frame (see Module 10.16). Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using A Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.7 Genetic information written in codons is translated into amino acid sequences
The flow of information from gene to protein is based on a triplet code. The genetic instructions for the amino acid sequence of a polypeptide chain are written in DNA and RNA as a series of nonoverlapping three-base “words” called codons. Translation involves switching from the nucleotide “language” to the amino acid “language.” Each amino acid is specified by a codon. 64 codons are possible. Some amino acids have more than one possible codon. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • The transcription of DNA into RNA is like a reporter who transcribes a political speech. In both situations, the language remains the same, although in the case of the reporter, it changes its form from spoken to written language. • The sequential information in DNA and RNA is analogous to the sequential information in the letters of a sentence. This analogy is also helpful when explaining the impact of insertion or deletion mutations that cause a shift in the reading frame (see Module 10.16). Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using A Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

DNA Transcription RNA Codon Translation Polypeptide Amino acid
Figure DNA A A A C C G G C A A A A Transcription RNA U U U G G C C G U U U U Codon Translation Figure Transcription and translation of codons (partial) Polypeptide Amino acid

10.8 The genetic code dictates how codons are translated into amino acids
The genetic code is the amino acid translations of each of the nucleotide triplets. Three nucleotides specify one amino acid. Sixty-one codons correspond to amino acids. AUG codes for methionine and signals the start of transcription. Three “stop” codons signal the end of translation. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • You may want to note the parallel between the discovery in 1799 of the Rosetta Stone, which provided the key that enabled scholars to crack the previously indecipherable hieroglyphic code, and the cracking of the genetic code in Consider challenging your students to explain what part of the genetic code is similar to the Rosetta Stone. This could be a short in-class activity for small groups. • The authors note the universal use of the genetic code in all forms of life. The evolutionary significance of this fundamental, universal language is a reminder of the shared ancestry of all life. The universal genetic code is part of the overwhelming evidence for evolution. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.8 The genetic code dictates how codons are translated into amino acids
The genetic code is redundant, with more than one codon for some amino acids, unambiguous, in that any codon for one amino acid does not code for any other amino acid, and nearly universal, in that the genetic code is shared by organisms from the simplest bacteria to the most complex plants and animals. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • You may want to note the parallel between the discovery in 1799 of the Rosetta Stone, which provided the key that enabled scholars to crack the previously indecipherable hieroglyphic code, and the cracking of the genetic code in Consider challenging your students to explain what part of the genetic code is similar to the Rosetta Stone. This could be a short in-class activity for small groups. • The authors note the universal use of the genetic code in all forms of life. The evolutionary significance of this fundamental, universal language is a reminder of the shared ancestry of all life. The universal genetic code is part of the overwhelming evidence for evolution. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Second base of RNA codon U C A G
Figure 10.8a Second base of RNA codon U C A G UUU UCU UAU UGU U C A G Phe Tyr Cys UUC UCC UAC UGC U Ser UUA UCA UAA Stop UGA Stop Leu UUG UCG UAG Stop UGG Trp CUU CCU CAU CGU U C A G His CUC CCC CAC CGC C Leu Pro Arg CUA CCA CAA CGA Gln First base of RNA codon Third base of RNA codon CUG CCG CAG CGG AUU ACU AAU AGU U C A G Ser Asn AUC lle ACC AAC AGC A Thr AUA Figure 10.8a The genetic code used to translate RNA codons to amino acids ACA AAA AGA Arg Lys AUG Met or start ACG AAG AGG GUU GCU GAU GGU U C A G Asp GUC GCC GAC GGC G Val Ala Gly GUA GCA GAA GGA Glu GUG GCG GAG GGG

Strand to be transcribed
Figure 10.8b-1 Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Figure 10.8b-1 Deciphering the genetic information in DNA (step 1)

Figure 10.8b-2 Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription RNA A U G A A G U U U U A G Figure 10.8b-2 Deciphering the genetic information in DNA (step 2)

Figure 10.8b-3 Strand to be transcribed T A C T T C A A A A T C DNA A T G A A G T T T T A G Transcription RNA A U G A A G U U U U A G Figure 10.8b-3 Deciphering the genetic information in DNA (step 3) Start codon Stop codon Translation Polypeptide Met Lys Phe

10.9 VISUALIZING THE CONCEPT: Transcription produces genetic messages in the form of RNA
Transcription of a gene occurs in three main steps: initiation, involving the attachment of RNA polymerase to the promoter and the start of RNA synthesis, elongation, as the newly formed RNA strand grows, and termination, when RNA polymerase reaches the terminator DNA and the polymerase molecule detaches from the newly made RNA strand and the gene. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. • As students learn about transcription, they might wonder which of the two strands of DNA is read. This uncertainty may add to the confusion about the details of the process, and students might not even think to ask. As noted in Module 10.9, the location of the promoter, a specific binding site for RNA polymerase, determines which strand is read. Teaching Tips • Another advantage to the use of RNA to direct protein synthesis is that the original code (DNA) remains safely within the nucleus, away from the many potentially damaging chemicals in the cytoplasm. This is like making photocopies of important documents for study, keeping the originals safely stored away. Active Lecture Tips  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Initiation Elongation Termination Figure 10.9-3
Direction of transcription RNA synthesis begins after RNA polymerase attaches to the promoter. Unused strand of DNA RNA polymerase Terminator DNA DNA of gene Newly formed RNA Template strand of DNA Promoter Elongation Direction of transcription Using the DNA as a template, RNA polymerase adds free RNA nucleotides one at a time. Free RNA nucleotide DNA strands reunite U A T C C A A T C G T A U G A U C C A A A T A G G T T A DNA strands separate Newly made RNA Figure Transcription of a gene (step 3) Termination RNA synthesis ends when RNA polymerase reaches the terminator DNA sequence. Terminator DNA Completed RNA RNA polymerase detaches

10.10 Eukaryotic RNA is processed before leaving the nucleus as mRNA
Messenger RNA (mRNA) encodes amino acid sequences and conveys genetic messages from DNA to the translation machinery of the cell. In prokaryotes, this occurs in the same place that mRNA is made. But in eukaryotes, mRNA must exit the nucleus via nuclear pores to enter the cytoplasm. Eukaryotic mRNA has introns, interrupting sequences that separate exons, the coding regions. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Many analogies can be developed to represent the selective expression of a gene requiring the deletion of introns. Instructors who only assign some modules of a chapter are treating the chapters like sections of exons and introns, portions to be read and portions to be skipped. Alternately, students who highlight a chapter might be thought of as editing the book into exons, portions to be reviewed, and introns, nonhighlighted sections that will not be studied. Both analogies are imperfect, but may still convey the concept of selective reading. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Eukaryotic mRNA undergoes processing before leaving the nucleus. RNA splicing removes introns (intervening sequences) and joins exons (expressed sequences) to produce a continuous coding sequence. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Many analogies can be developed to represent the selective expression of a gene requiring the deletion of introns. Instructors who only assign some modules of a chapter are treating the chapters like sections of exons and introns, portions to be read and portions to be skipped. Alternately, students who highlight a chapter might be thought of as editing the book into exons, portions to be reviewed, and introns, nonhighlighted sections that will not be studied. Both analogies are imperfect, but may still convey the concept of selective reading. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

A cap and tail of extra nucleotides are added to the ends of the mRNA to facilitate the export of the mRNA from the nucleus, protect the mRNA from degradation by cellular enzymes, and help ribosomes bind to the mRNA. The cap and tail themselves are not translated into protein. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Many analogies can be developed to represent the selective expression of a gene requiring the deletion of introns. Instructors who only assign some modules of a chapter are treating the chapters like sections of exons and introns, portions to be read and portions to be skipped. Alternately, students who highlight a chapter might be thought of as editing the book into exons, portions to be reviewed, and introns, nonhighlighted sections that will not be studied. Both analogies are imperfect, but may still convey the concept of selective reading. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Transcription Addition of cap and tail
Figure 10.10 Exon Exon Exon Intron DNA Intron Transcription Addition of cap and tail Cap RNA transcript with cap and tail Introns removed Tail Exons spliced together mRNA Coding sequence Figure The production of eukaryotic mRNA NUCLEUS CYTOPLASM

10.11 Transfer RNA molecules serve as interpreters during translation
Transfer RNA (tRNA) molecules function as an interpreter, converting the genetic message of mRNA into the language of proteins. Transfer RNA molecules perform this interpreter task by picking up the appropriate amino acid and using a special triplet of bases, called an anticodon, to recognize the appropriate codons in the mRNA. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • The unique structure of tRNA, with binding sites for an amino acid and its codon, permits the translation of the genetic code. Like an interpreter who speaks two languages, the tRNA molecules match codons to the specified amino acid. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.12 Ribosomes build polypeptides
Translation occurs on the surface of the ribosome. Ribosomes coordinate the functioning of mRNA and tRNA and, ultimately, the synthesis of polypeptides. Ribosomes have two subunits: small and large. Each subunit is composed of ribosomal RNAs and proteins. Ribosomal subunits come together during translation. Ribosomes have binding sites for mRNA and tRNAs. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Students might wonder why the details of transcription and translation are important. As the text notes, differences in the composition of prokaryotic and eukaryotic ribosomes form the basis of action for antibiotics. By identifying differences, we can develop drugs that target crucial features of prokaryotic pathogens without harming their eukaryotic hosts. • Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text but may be required to fill out your explanations. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

The next amino acid to be added to the polypeptide
Figure Growing polypeptide tRNA binding sites tRNA molecules Ribosome Large subunit P site A site Small subunit mRNA binding site Growing polypeptide The next amino acid to be added to the polypeptide Figure Two representations of a ribosome with empty binding sites (top) and a ribosome with occupied binding sites (bottom) mRNA tRNA Codons

10.12 Ribosomes build polypeptides
The ribosomes of bacteria and eukaryotes are very similar in function. Those of eukaryotes are slightly larger and different in composition. The differences are medically significant. Certain antibiotic drugs can inactivate bacterial ribosomes while leaving eukaryotic ribosomes unaffected. These drugs, such as tetracycline and streptomycin, are used to combat bacterial infections. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Students might wonder why the details of transcription and translation are important. As the text notes, differences in the composition of prokaryotic and eukaryotic ribosomes form the basis of action for antibiotics. By identifying differences, we can develop drugs that target crucial features of prokaryotic pathogens without harming their eukaryotic hosts. • Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text but may be required to fill out your explanations. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.13 An initiation codon marks the start of an mRNA message
Translation can be divided into the same three phases as transcription: initiation, elongation, and termination. Initiation brings together mRNA, a tRNA bearing the first amino acid, and the two subunits of a ribosome. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text but may be required to fill out your explanations. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Initiation establishes where translation will begin. Initiation occurs in two steps. An mRNA molecule binds to a small ribosomal subunit, and a special initiator tRNA binds to mRNA at the start codon. The start codon reads AUG and codes for methionine. The first tRNA has the anticodon UAC. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text but may be required to fill out your explanations. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Initiation establishes where translation will begin. Initiation occurs in two steps. A large ribosomal subunit joins the small subunit, allowing the ribosome to function. The first tRNA occupies the P site, which will hold the growing polypeptide. The A site is available to receive the next amino- acid-bearing tRNA. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Ribosomal RNA is transcribed in the nucleolus of eukaryotic cells. The ribosomal subunits are assembled in the nucleus using proteins imported from the cytosol. These subunits are then exported to the cytosol, where they are only assembled into a functional ribosome when they attach to an mRNA molecule. Some of these details are not specifically noted in the text but may be required to fill out your explanations. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. © 2015 Pearson Education, Inc.

Start of genetic message
Figure 10.13a Start of genetic message Cap End Figure 10.13a A molecule of eukaryotic mRNA Tail

Small ribosomal subunit
Figure 10.13b-1 Met Initiator tRNA mRNA U A C A U G Start codon Small ribosomal subunit Figure 10.13b-1 The initiation of translation (step 1) 1

Large ribosomal subunit
Figure 10.13b-2 Met Met Large ribosomal subunit Initiator tRNA P site A site mRNA U A C U A C A U G A U G Start codon Small ribosomal subunit Figure 10.13b-2 The initiation of translation (step 2) 1 2

10.14 Elongation adds amino acids to the polypeptide chain until a stop codon terminates translation
Once initiation is complete, amino acids are added one by one to the first amino acid. Each addition occurs in a three-step elongation process. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Students might want to think of the A and P sites as stages in an assembly line. The A site is where a new amino acid is brought in, according to the blueprint of the codon on the mRNA. The P site is where the growing product/polypeptide is anchored as it is being built. To help students better remember details of translation, they might think of the letters for the two sites as meaning A for addition, where an amino acid is added, and P for polypeptide, where the growing polypeptide is located. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Each cycle of elongation has three steps. The anticodon of an incoming tRNA molecule, carrying its amino acid, pairs with the mRNA codon in the A site of the ribosome. The polypeptide separates from the tRNA in the P site and attaches by a new peptide bond to the amino acid carried by the tRNA in the A site. The P site tRNA (now lacking an amino acid) leaves the ribosome, and the ribosome translocates (moves) the remaining tRNA (which has the growing polypeptide) from the A site to the P site. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Students might want to think of the A and P sites as stages in an assembly line. The A site is where a new amino acid is brought in, according to the blueprint of the codon on the mRNA. The P site is where the growing product/polypeptide is anchored as it is being built. To help students better remember details of translation, they might think of the letters for the two sites as meaning A for addition, where an amino acid is added, and P for polypeptide, where the growing polypeptide is located. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Peptide bond formation
Figure Amino acid Polypeptide Anticodon P site A site mRNA Codons 1 Codon recognition mRNA movement Stop codon Figure Polypeptide elongation (step 4) New peptide bond 2 Peptide bond formation 3 Translocation

Elongation continues until the termination stage of translation, when the ribosome reaches a stop codon, the completed polypeptide is freed from the last tRNA, and the ribosome splits back into its separate subunits. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • Students might want to think of the A and P sites as stages in an assembly line. The A site is where a new amino acid is brought in, according to the blueprint of the codon on the mRNA. The P site is where the growing product/polypeptide is anchored as it is being built. To help students better remember details of translation, they might think of the letters for the two sites as meaning A for addition, where an amino acid is added, and P for polypeptide, where the growing polypeptide is located. • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

10.15 Review: The flow of genetic information in the cell is DNA  RNA  protein
The flow of genetic information is from DNA to RNA to protein. In transcription (DNA → RNA), the mRNA is synthesized on a DNA template. In eukaryotic cells, transcription occurs in the nucleus, and the messenger RNA is processed before it travels to the cytoplasm. In prokaryotes, transcription occurs in the cytoplasm. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • After translation is addressed, consider asking your students (working in small groups) to list all of the places where base pairing is used (in the construction of a DNA molecule during DNA replication, in transcription, and during translation when the tRNA attaches).

10.15 Review: The flow of genetic information in the cell is DNA  RNA  protein
Translation can be divided into four steps, all of which occur in the cytoplasm: amino acid attachment, initiation of polypeptide synthesis, elongation, and termination. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. Teaching Tips • If you use a train analogy for the assembly of monomers into polymers, the DNA and RNA trains are traded in on a three-for-one basis for the polypeptide train during translation. In general, this produces polypeptides that have about one-third as many monomers as the mRNA that coded for them. Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Baking Cookies Describes the Central Dogma on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Using a Food Analogy to Think About Protein Synthesis on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Students Perform a Protein Synthesis Play on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity. • After translation is addressed, consider asking your students (working in small groups) to list all of the places where base pairing is used (in the construction of a DNA molecule during DNA replication, in transcription, and during translation when the tRNA attaches).

Figure 10.15-5 A summary of transcription and translation (step 5)
DNA Transcription NUCLEUS mRNA 1 Transcription RNA polymerase Translation CYTOPLASM Amino acid Amino acid attachment 2 Enzyme tRNA ATP Initiator tRNA Anticodon Large ribosomal subunit Initiation of polypeptide synthesis 3 U A C A U G Start codon Small ribosomal subunit mRNA New peptide bond forming Growing polypeptide 4 Elongation Figure A summary of transcription and translation (step 5) Codons mRNA Polypeptide 5 Termination Stop codon

10.16 Mutations can affect genes
A mutation is any change in the nucleotide sequence of DNA. Mutations can involve large chromosomal regions or just a single nucleotide pair. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. • Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips • A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame is reformed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. • The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Demonstrating a Frame Shift Mutation on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Mutations within a gene can be divided into two general categories. Nucleotide substitutions involve the replacement of one nucleotide and its base-pairing partner with another pair of nucleotides. Base substitutions may have no effect at all, producing a silent mutation, change the amino acid coding, producing a missense mutation, which produces a different amino acid, lead to a base substitution that produces an improved protein that enhances the success of the mutant organism and its descendants, or change an amino acid into a stop codon, producing a nonsense mutation. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. • Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips • A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame is reformed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. • The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Demonstrating a Frame Shift Mutation on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Nucleotide insertions or deletions of one or more nucleotides in a gene may cause a frameshift mutation, which alters the reading frame (triplet grouping) of the genetic message, lead to significant changes in amino acid sequence, and produce a nonfunctional polypeptide. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. • Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips • A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame is reformed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. • The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Demonstrating a Frame Shift Mutation on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Mutagenesis is the production of mutations. Mutations can be caused by spontaneous errors that occur during DNA replication or recombination or by mutagens, which include high-energy radiation such as X-rays and ultraviolet light and chemicals. Student Misconceptions and Concerns • Beginning college students are often intensely focused on writing detailed notes. The risk is that they will miss the overall patterns and the broader significance of the topics discussed. Consider a gradual approach to the subjects of transcription and translation, beginning quite generally and testing comprehension, before venturing into the finer mechanics of each process. • Mutations are often discussed as part of evolutionary mechanisms. In this sense, mutations may be considered a part of a creative process. The dual nature of mutations, potentially deadly yet potentially innovative, should be clarified. Teaching Tips • A simple way to demonstrate the effect of a reading frame shift is to have students compare the following three sentences. The first is a simple sentence. However, look what happens when a letter is added (2) or deleted (3). The reading frame is reformed into nonsense. (1) The big red pig ate the red rag. (2) The big res dpi gat eth ere dra g. (3) The big rep iga tet her edr ag. • The authors have noted elsewhere that “A random mutation is like a random shot in the dark. It is not likely to improve a genome any more than shooting a bullet through the hood of a car is likely to improve engine performance!” Active Lecture Tips  See the Media Review: “Learn.Genetics” Genetic Science Learning from the University of Utah on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.  See the Activity Demonstrating a Frame Shift Mutation on the Instructor Exchange. Visit the Instructor Exchange in the MasteringBiology instructor resource area for a description of this activity.

Sickle-cell hemoglobin
Figure 10.16a Normal hemoglobin DNA Mutant hemoglobin DNA C T T C A T mRNA mRNA G A A G U A Figure 10.16a The molecular basis of sickle-cell disease Normal hemoglobin Sickle-cell hemoglobin Glu Val

Nucleotide substitution A U G A A G U U U A G C G C A
Figure 10.16b-0 Normal gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala Nucleotide substitution A U G A A G U U U A G C G C A Met Lys Phe Ser Ala Deleted U Nucleotide deletion A U G A A G U U G G C G C A Met Lys Leu Ala Figure 10.16b-0 Types of mutations and their effects Inserted G Nucleotide insertion A U G A A G U U U G G C G C Met Lys Leu Trp Arg

Nucleotide substitution A U G A A G U U U A G C G C A
Figure 10.16b-1 Normal gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala Nucleotide substitution A U G A A G U U U A G C G C A Figure 10.16b-1 Types of mutations and their effects (part 1) Met Lys Phe Ser Ala

Normal gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly
Figure 10.16b-2 Normal gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala Deleted U Nucleotide deletion A U G A A G U U G G C G C A Figure 10.16b-2 Types of mutations and their effects (part 2) Met Lys Leu Ala

Normal gene mRNA Protein Nucleotide insertion
Figure 10.16b-3 Normal gene A U G A A G U U U G G C G C A mRNA Protein Met Lys Phe Gly Ala Inserted G Nucleotide insertion A U G A A G U U U G G C G C Figure 10.16b-3 Types of mutations and their effects (part 3) Met Lys Leu Trp Arg

The Structure of the Genetic Material

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