Copyright Pearson Prentice Hall 12–1 DNA Photo credit: Jacob Halaska/Index Stock Imagery, Inc. Copyright Pearson Prentice Hall

Griffith and Transformation In 1928, British scientist Fredrick Griffith was trying to learn how certain types of bacteria caused pneumonia. He isolated two different strains of pneumonia bacteria from mice and grew them in his lab. Copyright Pearson Prentice Hall

Griffith and Transformation Griffith made two observations: (1) The disease-causing strain of bacteria grew into smooth colonies on culture plates. (2) The harmless strain grew into colonies with rough edges. Copyright Pearson Prentice Hall

Griffith and Transformation Griffith's Experiments Griffith set up four individual experiments. Experiment 1: Mice were injected with the disease-causing strain of bacteria. The mice developed pneumonia and died. Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Copyright Pearson Prentice Hall

Griffith and Transformation Experiment 2: Mice were injected with the harmless strain of bacteria. These mice didn’t get sick. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Lives Copyright Pearson Prentice Hall

Griffith and Transformation Experiment 3: Griffith heated the disease-causing bacteria. He then injected the heat-killed bacteria into the mice. The mice survived. Heat-killed disease-causing bacteria (smooth colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Lives Copyright Pearson Prentice Hall

Griffith and Transformation Heat-killed disease-causing bacteria (smooth colonies) Experiment 4: Griffith mixed his heat-killed, disease-causing bacteria with live, harmless bacteria and injected the mixture into the mice. The mice developed pneumonia and died. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Live disease-causing bacteria (smooth colonies) Dies of pneumonia Copyright Pearson Prentice Hall

Griffith and Transformation Heat-killed disease-causing bacteria (smooth colonies) Griffith concluded that the heat-killed bacteria passed their disease-causing ability to the harmless strain. Harmless bacteria (rough colonies) Griffith injected mice with four different samples of bacteria. When injected separately, neither heat-killed, disease-causing bacteria nor live, harmless bacteria killed the mice. The two types injected together, however, caused fatal pneumonia. From this experiment, biologists inferred that genetic information could be transferred from one bacterium to another. Live disease-causing bacteria (smooth colonies) Dies of pneumonia Copyright Pearson Prentice Hall

Griffith and Transformation Griffith called this process transformation because one strain of bacteria (the harmless strain) had changed permanently into another (the disease-causing strain). Griffith hypothesized that a factor must contain information that could change harmless bacteria into disease-causing ones. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Avery and DNA Avery and DNA Oswald Avery repeated Griffith’s work to determine which molecule was most important for transformation. Avery and his colleagues made an extract from the heat-killed bacteria that they treated with enzymes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Avery and DNA The enzymes destroyed proteins, lipids, carbohydrates, and other molecules, including the nucleic acid RNA. Transformation still occurred. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Avery and DNA Avery and other scientists repeated the experiment using enzymes that would break down DNA. When DNA was destroyed, transformation did not occur. Therefore, they concluded that DNA was the transforming factor. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Avery and DNA Avery and other scientists discovered that the nucleic acid DNA stores and transmits the genetic information from one generation of an organism to the next. Copyright Pearson Prentice Hall

The Hershey-Chase Experiment Alfred Hershey and Martha Chase studied viruses—nonliving particles smaller than a cell that can infect living organisms. Copyright Pearson Prentice Hall

The Hershey-Chase Experiment Bacteriophages  A virus that infects bacteria is known as a bacteriophage. Bacteriophages are composed of a DNA or RNA core and a protein coat. Copyright Pearson Prentice Hall

The Hershey-Chase Experiment They grew viruses in cultures containing radioactive isotopes of phosphorus-32 (32P) and sulfur-35 (35S). Copyright Pearson Prentice Hall

The Hershey-Chase Experiment If 35S was found in the bacteria, it would mean that the viruses’ protein had been injected into the bacteria. Alfred Hershey and Martha Chase used different radioactive markers to label the DNA and proteins of bacteriophages. The bacteriophages injected only DNA into the bacteria, not proteins. From these results, Hershey and Chase concluded that the genetic material of the bacteriophage was DNA. Phage infects bacterium Bacteriophage with suffur-35 in protein coat No radioactivity inside bacterium Copyright Pearson Prentice Hall

The Hershey-Chase Experiment If 32P was found in the bacteria, then it was the DNA that had been injected. Alfred Hershey and Martha Chase used different radioactive markers to label the DNA and proteins of bacteriophages. The bacteriophages injected only DNA into the bacteria, not proteins. From these results, Hershey and Chase concluded that the genetic material of the bacteriophage was DNA. Bacteriophage with phosphorus-32 in DNA Phage infects bacterium Radioactivity inside bacterium Copyright Pearson Prentice Hall

The Hershey-Chase Experiment Nearly all the radioactivity in the bacteria was from phosphorus (32P). Hershey and Chase concluded that the genetic material of the bacteriophage was DNA, not protein. Copyright Pearson Prentice Hall

The Components and Structure of DNA DNA is made up of nucleotides. A nucleotide is a monomer of nucleic acids made up of: Deoxyribose – 5-carbon Sugar Phosphate Group Nitrogenous Base Copyright Pearson Prentice Hall

The Components and Structure of DNA There are four kinds of bases in in DNA: adenine guanine cytosine thymine DNA is made up of nucleotides. Each nucleotide has three parts: a deoxyribose molecule, a phosphate group, and a nitrogenous base. There are four different bases in DNA: adenine, guanine, cytosine, and thymine. Copyright Pearson Prentice Hall

The Components and Structure of DNA Chargaff's Rules Erwin Chargaff discovered that: The percentages of guanine [G] and cytosine [C] bases are almost equal in any sample of DNA. The percentages of adenine [A] and thymine [T] bases are almost equal in any sample of DNA. Copyright Pearson Prentice Hall

The Components and Structure of DNA X-Ray Evidence  Rosalind Franklin used X-ray diffraction to get information about the structure of DNA. She aimed an X-ray beam at concentrated DNA samples and recorded the scattering pattern of the X-rays on film. This X-ray diffraction photograph of DNA was taken by Rosalind Franklin in the early 1950s. The X-shaped pattern in the center indicates that the structure of DNA is helical. Photo credit: ©Cold Spring Harbor Laboratory Archives/Peter Arnold, Inc. Copyright Pearson Prentice Hall

The Components and Structure of DNA The Double Helix  Using clues from Franklin’s pattern, James Watson and Francis Crick built a model that explained how DNA carried information and could be copied. Watson and Crick's model of DNA was a double helix, in which two strands were wound around each other. Copyright Pearson Prentice Hall

The Components and Structure of DNA DNA Double Helix DNA is a double helix in which two strands are wound around each other. Each strand is made up of a chain of nucleotides. The two strands are held together by hydrogen bonds between adenine and thymine and between guanine and cytosine. Copyright Pearson Prentice Hall

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The Components and Structure of DNA Watson and Crick discovered that hydrogen bonds can form only between certain base pairs—adenine and thymine, and guanine and cytosine. This principle is called base pairing. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–1 Avery and other scientists discovered that DNA is found in a protein coat. DNA stores and transmits genetic information from one generation to the next. transformation does not affect bacteria. proteins transmit genetic information from one generation to the next. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–1 The Hershey-Chase experiment was based on the fact that DNA has both sulfur and phosphorus in its structure. protein has both sulfur and phosphorus in its structure. both DNA and protein have no phosphorus or sulfur in their structure. DNA has only phosphorus, while protein has only sulfur in its structure. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–1 DNA is a long molecule made of monomers called nucleotides. purines. pyrimidines. sugars. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–1 Chargaff's rules state that the number of guanine nucleotides must equal the number of cytosine nucleotides. adenine nucleotides. thymine nucleotides. thymine plus adenine nucleotides. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–1 In DNA, the following base pairs occur: A with C, and G with T. A with T, and C with G. A with G, and C with T. A with T, and C with T. Copyright Pearson Prentice Hall

12-2 Chromosomes and DNA Replication Photo credit: Jacob Halaska/Index Stock Imagery, Inc. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA and Chromosomes DNA and Chromosomes In prokaryotic cells, DNA is located in the cytoplasm. Most prokaryotes have a single DNA molecule containing nearly all of the cell’s genetic information. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA and Chromosomes Chromosome Most prokaryotes, such as this E. coli bacterium, have only a single circular chromosome. This chromosome holds most of the organism’s DNA. E. Coli Bacterium Bases on the Chromosomes Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA and Chromosomes Many eukaryotes have 1000 times the amount of DNA as prokaryotes. Eukaryotic DNA is located in the cell nucleus inside chromosomes. The number of chromosomes varies widely from one species to the next. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA and Chromosomes Chromosome Structure Eukaryotic chromosomes contain DNA and protein, tightly packed together to form chromatin. Chromatin consists of DNA tightly coiled around proteins called histones. DNA and histone molecules form nucleosomes. Nucleosomes pack together, forming a thick fiber. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA and Chromosomes Eukaryotic Chromosome Structure Chromosome Nucleosome DNA double helix Coils Supercoils Eukaryotic chromosomes contain DNA wrapped around proteins called histones. The strands of nucleosomes are tightly coiled and supercoiled to form chromosomes. Histones Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication DNA Replication Each strand of the DNA double helix has all the information needed to reconstruct the other half by the mechanism of base pairing. In most prokaryotes, DNA replication begins at a single point and continues in two directions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication In eukaryotic chromosomes, DNA replication occurs at hundreds of places. Replication proceeds in both directions until each chromosome is completely copied. The sites where separation and replication occur are called replication forks. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication Duplicating DNA  Before a cell divides, it duplicates its DNA in a process called replication. Replication ensures that each resulting cell will have a complete set of DNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication During DNA replication, the DNA molecule separates into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of DNA serves as a template for the new strand. Copyright Pearson Prentice Hall

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Copyright Pearson Prentice Hall DNA Replication New Strand Original strand Nitrogen Bases Growth Growth During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand. Replication Fork Replication Fork DNA Polymerase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication How Replication Occurs DNA replication is carried out by enzymes that “unzip” a molecule of DNA. Hydrogen bonds between base pairs are broken and the two strands of DNA unwind. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication New Strand Original strand Nitrogen Bases Growth Growth During DNA replication, the DNA molecule produces two new complementary strands. Each strand of the double helix of DNA serves as a template for the new strand. Replication Fork Replication Fork DNA Polymerase Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall DNA Replication The principal enzyme involved in DNA replication is DNA polymerase. DNA polymerase joins individual nucleotides to produce a DNA molecule and then “proofreads” each new DNA strand. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–2 In prokaryotic cells, DNA is found in the cytoplasm. nucleus. ribosome. cell membrane. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–2 The first step in DNA replication is producing two new strands. separating the strands. producing DNA polymerase. correctly pairing bases. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–2 A DNA molecule separates, and the sequence GCGAATTCG occurs in one strand. What is the base sequence on the other strand? GCGAATTCG CGCTTAAGC TATCCGGAT GATGGCCAG Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–2 In addition to carrying out the replication of DNA, the enzyme DNA polymerase also functions to unzip the DNA molecule. regulate the time copying occurs in the cell cycle. “proofread” the new copies to minimize the number of mistakes. wrap the new strands onto histone proteins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–2 The structure that may play a role in regulating how genes are “read” to make a protein is the coil. histone. nucleosome. chromatin. Copyright Pearson Prentice Hall

12-3 RNA and Protein Synthesis Copyright Pearson Prentice Hall

12–3 RNA and Protein Synthesis Genes are coded DNA instructions that control the production of proteins. Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA. RNA contains coded information for making proteins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Structure of RNA The Structure of RNA There are three main differences between RNA and DNA: The sugar in RNA is ribose instead of deoxyribose. RNA is generally single-stranded. RNA contains uracil in place of thymine. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA Types of RNA There are three main types of RNA: messenger RNA ribosomal RNA transfer RNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Messenger RNA (mRNA) carries copies of instructions for assembling amino acids into proteins. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Types of RNA Ribosome Ribosomal RNA The three main types of RNA are messenger RNA, ribosomal RNA, and transfer RNA. Ribosomal RNA is combined with proteins to form ribosomes. Ribosomes are made up of proteins and ribosomal RNA (rRNA). Copyright Pearson Prentice Hall

Protein Synthesis DNA molecule DNA strand (template) 3¢ 5¢ TRANSCRIPTION mRNA 5¢ 3¢ Codon TRANSLATION Protein Amino acid

Copyright Pearson Prentice Hall Transcription Transcription DNA is copied in the form of RNA This first process is called transcription. The process begins at a section of DNA called a promoter. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Transcription RNA RNA polymerase DNA During transcription, RNA polymerase uses one strand of DNA as a template to assemble nucleotides into a strand of RNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall RNA Editing RNA Editing Some DNA within a gene is not needed to produce a protein. These areas are called introns. The DNA sequences that code for proteins are called exons. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall RNA Editing The introns are cut out of RNA molecules. The exons are the spliced together to form mRNA. Exon Intron DNA Pre-mRNA mRNA Many RNA molecules have sections, called introns, edited out of them before they become functional. The remaining pieces, called exons, are spliced together. Then, a cap and tail are added to form the final RNA molecule. Cap Tail Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code The Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” (the bases: A, U, C, and G). Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code A codon consists of three consecutive nucleotides on mRNA that specify a particular amino acid. A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Genetic Code The genetic code shows the amino acid to which each of the 64 possible codons corresponds. To decode a codon, start at the middle of the circle and move outward. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Translation Translation Translation is the decoding of an mRNA message into a polypeptide chain (protein). Translation takes place on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins. Nucleus mRNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Translation The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. Lysine Phenylalanine tRNA Methionine Ribosome During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Start codon Copyright Pearson Prentice Hall

Translation direction Protein Synthesis Lysine tRNA During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Translation direction Ribosome Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Translation The process continues until the ribosome reaches a stop codon. Polypeptide Ribosome tRNA During translation, or protein synthesis, the cell uses information from messenger RNA to produce proteins. The cell uses all three main forms of RNA during this process. mRNA Copyright Pearson Prentice Hall

Amino acids within a polypeptide Genes and Proteins Codon Codon Codon DNA mRNA Protein Single strand of DNA Codon Codon Codon mRNA This diagram illustrates how information for specifying the traits of an organism is carried in DNA. The sequence of bases in DNA is used as a template for mRNA. The codons of mRNA specify the sequence of amino acids in a protein, and proteins play a key role in producing an organism’s traits. Alanine Arginine Leucine Amino acids within a polypeptide Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 The role of a master plan in a building is similar to the role of which molecule? messenger RNA DNA transfer RNA ribosomal RNA Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A base that is present in RNA but NOT in DNA is thymine. uracil. cytosine. adenine. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 The nucleic acid responsible for bringing individual amino acids to the ribosome is transfer RNA. DNA. messenger RNA. ribosomal RNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A region of a DNA molecule that indicates to an enzyme where to bind to make RNA is the intron. exon. promoter. codon. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–3 A codon typically carries sufficient information to specify a(an) single base pair in RNA. single amino acid. entire protein. single base pair in DNA. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 Mutations 12-4 Mutations Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12-4 Mutations Mutations are changes in the genetic material. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Kinds of Mutations Mutations that produce changes in a single gene are known as gene mutations. Mutations that produce changes in whole chromosomes are known as chromosomal mutations. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Gene Mutations  Gene mutations involving a change in one or a few nucleotides are known as point mutations because they occur at a single point in the DNA sequence. Point mutations include substitutions, insertions, and deletions. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Substitutions usually affect no more than a single amino acid. Gene mutations result from changes in a single gene. In a substitution, one base replaces another. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations The effects of insertions or deletions are more dramatic. The addition or deletion of a nucleotide causes a shift in the grouping of codons. Changes like these are called frameshift mutations. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations In an insertion, an extra base is inserted into a base sequence. Gene mutations result from changes in a single gene. In an insertion, an extra base is inserted into a base sequence. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations In a deletion, the loss of a single base is deleted and the reading frame is shifted. Gene mutations result from changes in a single gene. The loss of a single letter in a sentence models the effects of the deletion of one base in a DNA sequence. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Chromosomal Mutations  Chromosomal mutations involve changes in the number or structure of chromosomes. Chromosomal mutations include deletions, duplications, inversions, and translocations. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Deletions involve the loss of all or part of a chromosome. Chromosomal mutations involve changes in whole chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Duplications produce extra copies of parts of a chromosome. Chromosomal mutations involve changes in whole chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Inversions reverse the direction of parts of chromosomes. Chromosomal mutations involve changes in whole chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall Kinds of Mutations Translocations occurs when part of one chromosome breaks off and attaches to another. Chromosomal mutations involve changes in whole chromosomes. Copyright Pearson Prentice Hall

Significance of Mutations Many mutations have little or no effect on gene expression. Some mutations are the cause of genetic disorders. Polyploidy is the condition in which an organism has extra sets of chromosomes. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 A mutation in which all or part of a chromosome is lost is called a(an) duplication. deletion. inversion. point mutation. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 A mutation that affects every amino acid following an insertion or deletion is called a(an) frameshift mutation. point mutation. chromosomal mutation. inversion. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 A mutation in which a segment of a chromosome is repeated is called a(an) deletion. inversion. duplication. point mutation. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 The type of point mutation that usually affects only a single amino acid is called a deletion. a frameshift mutation. an insertion. a substitution. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–4 When two different chromosomes exchange some of their material, the mutation is called a(an) inversion. deletion. substitution. translocation. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12-5 Gene Regulation Fruit fly chromosome Mouse chromosomes 12-5 Gene Regulation Fruit fly embryo Mouse embryo Adult fruit fly Adult mouse Copyright Pearson Prentice Hall

Gene Regulation: An Example E. coli provides an example of how gene expression can be regulated. An operon is a group of genes that operate together. In E. coli, these genes must be turned on so the bacterium can use lactose as food. Therefore, they are called the lac operon. Copyright Pearson Prentice Hall

Gene Regulation: An Example How are lac genes turned off and on? Copyright Pearson Prentice Hall

Gene Regulation: An Example The lac genes are turned off by repressors and turned on by the presence of lactose. Copyright Pearson Prentice Hall

Gene Regulation: An Example On one side of the operon's three genes are two regulatory regions. In the promoter (P) region, RNA polymerase binds and then begins transcription. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example The other region is the operator (O). The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example When the lac repressor binds to the O region, transcription is not possible. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example When lactose is added, sugar binds to the repressor proteins. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example The repressor protein changes shape and falls off the operator and transcription is made possible. The lac genes in E. coli are turned off by repressors and turned on by the presence of lactose. When lactose is not present, the repressor binds to the operator region, preventing RNA polymerase from beginning transcription. Lactose causes the repressor to be released from the operator region. Copyright Pearson Prentice Hall

Gene Regulation: An Example Many genes are regulated by repressor proteins. Some genes use proteins that speed transcription. Sometimes regulation occurs at the level of protein synthesis. Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation How are most eukaryotic genes controlled? Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Operons are generally not found in eukaryotes.    Most eukaryotic genes are controlled individually and have regulatory sequences that are much more complex than those of the lac operon. Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Many eukaryotic genes have a sequence called the TATA box. TATA box Upstream enhancer Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation The TATA box seems to help position RNA polymerase. Upstream enhancer TATA box Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Eukaryotic promoters are usually found just before the TATA box, and consist of short DNA sequences. Upstream enhancer TATA box Introns Promoter sequences Exons Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. Eukaryotic genes have regulatory sequences that are more complex than prokaryotic genes. Direction of transcription Copyright Pearson Prentice Hall

Eukaryotic Gene Regulation Genes are regulated in a variety of ways by enhancer sequences. Many proteins can bind to different enhancer sequences. Some DNA-binding proteins enhance transcription by: opening up tightly packed chromatin helping to attract RNA polymerase blocking access to genes. Copyright Pearson Prentice Hall

Development and Differentiation As cells grow and divide, they undergo differentiation, meaning they become specialized in structure and function. Hox genes control the differentiation of cells and tissues in the embryo. Copyright Pearson Prentice Hall

Development and Differentiation Careful control of expression in hox genes is essential for normal development. All hox genes are descended from the genes of common ancestors. Copyright Pearson Prentice Hall

Development and Differentiation Hox Genes Fruit fly chromosome Mouse chromosomes Fruit fly embryo Mouse embryo n fruit flies, a series of hox genes along a chromosome determines the basic structure of the fly’s body. Mice have very similar genes on four different chromosomes. The color bars along the mouse’s back show the approximate body area affected by genes of the corresponding colors. Adult fruit fly Adult mouse Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–5 Which sequence shows the typical organization of a single gene site on a DNA strand? start codon, regulatory site, promoter, stop codon regulatory site, promoter, start codon, stop codon start codon, promoter, regulatory site, stop codon promoter, regulatory site, start codon, stop codon Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–5 A group of genes that operates together is a(an) promoter. operon. operator. intron. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–5 Repressors function to turn genes off. produce lactose. turn genes on. slow cell division. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–5 Which of the following is unique to the regulation of eukaryotic genes? promoter sequences TATA box different start codons regulatory proteins Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 12–5 Organs and tissues that develop in various parts of embryos are controlled by regulation sites. RNA polymerase. hox genes. DNA polymerase. Copyright Pearson Prentice Hall