1. THE STRUCTURE OF THE GENETIC MATERIAL
Figure
THE STRUCTURE OF THE GENETIC MATERIAL
Figure Why are viral diseases such a constant threat? (photo: influenza virus)

2. Learner Outcomes I Can……
Describe the experiments of Griffith, Hershey, and Chase, which supported the idea that DNA was life’s genetic material.
Compare the structures of DNA and RNA.

3. 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).

4. 10.1 SCIENTIFIC THINKING: Experiments showed that DNA is the genetic material
Biologists finally established the role of DNA in heredity through experiments with bacteria & viruses.
This breakthrough led to 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).

5. 10.1 SCIENTIFIC THINKING: Experiments showed that DNA is the genetic material
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.
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).

6. 10.1 SCIENTIFIC THINKING: Experiments showed that DNA is the genetic material
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.
The sulfur-labeled protein stayed with the phages outside the bacterial cell, while the phosphorus-labeled DNA was detected inside cells.
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).

7. Animation: Hershey-Chase Experiment

8. 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.

9. 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

10. 10.2 DNA and RNA are polymers of nucleotides
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.

11. 10.2 DNA and RNA are polymers of nucleotides
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.

12. Animation: DNA and RNA Structure

13. 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

14. 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.

15. 10.3 DNA is a double-stranded helix
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.

16. 10.3 DNA is a double-stranded helix
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.

17. 10.3 DNA is a double-stranded helix
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 nitrogen base pairs 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.

18. 10.3 DNA is a double-stranded helix
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.

19. DNA Replication

20. I Can…. Explain how the structure of DNA facilitates its replication.
Describe the process of DNA replication.

21. 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.

22. Animation: DNA Replication Overview

23. 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.
DNA Helicase, an enzyme/protein, initiates DNA replication
attach to the DNA at the origin of replication and
separate the two strands of the double helix.
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.

24. Two daughter DNA molecules
Figure 10.5a
Parental DNA molecule
Origin of replication
Parental strand
Daughter strand
“Bubble”
Figure 10.5a Multiple bubbles in replicating DNA
Two daughter DNA molecules

25. 10.5 DNA replication proceeds in two directions at many sites simultaneously
DNA replication occurs in the 5 to 3 direction.
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.

26. 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

27. 10.5 DNA replication proceeds in two directions at many sites simultaneously
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.

28. Animation: DNA Replication Review