Interest Grabber Order! Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units.

Interest Grabber

Order! Order!

Genes are made of DNA, a large, complex molecule. DNA is composed of individual units called nucleotides. Three of these units form a code. The order, or sequence, of a code and the type of code determine the meaning of the message.

Section 12-1

1. On a sheet of paper, write the word cats. List the letters or units that make up the word cats.

2. Try rearranging the units to form other words. Remember that eachnew word can have only three units. Write each word on your paper, and then add a definition for each word.

3. Did any of the codes you formed have the same meaning?4. How do you think changing the order of the nucleotides in the DNA

codon changes the codon’s message?

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Section Outline

12–1 DNAA. Griffith and Transformation

1. Griffith’s Experiments

2. Transformation

B. Avery and DNA

C. The Hershey-Chase Experiment

1. Bacteriophages

2. Radioactive Markers

D. The Structure of DNA

1. Chargaff’s Rules

2. X-Ray Evidence

3. The Double Helix

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Objectives

1. Be able to define transformation, bacteriophage, nucleotide, and base pairing.

2. Be able to describe the Griffith, Avery, and Hershey-Chase experiments.

3. Be able to explain what scientists discovered about the relationship between genes and DNA.

4. Be able to explain the overall structure of the DNA molecule.

Vocabulary Words

Transformation – process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria

Bacteriophage – a kind of virus that infects and kills bacteria

Nucleotide – monomer of nucleic acids made up of a 5-carbon sugar, a phosphate group, and a nitrogenous base

Base pairing – principle that bonds in DNA can form only between adenine and thymine and between guanine and cytosine

Griffith and Transformation

Griffith (mice injected with bacteria) – genetic information could be transformed from one bacterium to another

Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

Figure 12–2 Griffith’s Experiment

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Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

Heat-killed, disease-causing bacteria (smooth colonies)

Control(no growth)

Heat-killed, disease-causing bacteria (smooth colonies)

Harmless bacteria (rough colonies)

Dies of pneumonia Lives Lives Live, disease-causingbacteria (smooth colonies)

Dies of pneumonia

Section 12-1

Figure 12–2 Griffith’s Experiment

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Avery and DNA

Avery (“juice” from heat-killed bacteria and enzymes) – DNA is the nucleic acid that stores and transmits the genetic information from one generation of an organism to the next

Alfred Hershey- Martha Chase

Hershey-Chase – genetic material of the bacteriophage is DNA, not protein

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Figure 12–4 Hershey-Chase Experiment

Section 12-1

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Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Figure 12–4 Hershey-Chase Experiment

Section 12-1

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Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Figure 12–4 Hershey-Chase Experiment

Section 12-1

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Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA Nucleotides

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Percentage of Bases in Four Organisms

Section 12-1

Source of DNA A T G CSource of DNA A T G C

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

Streptococcus 29.8 31.6 20.5 18.0

Yeast 31.3 32.9 18.7 17.1

Herring 27.8 27.5 22.2 22.6

Human 30.9 29.4 19.9 19.8

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Sugar-Phosphate Backbone and Chargaff’s Rule

Chargaff’s Rules: If there are a certain number of cytosines, there will be about the same number of guanines. Same with A’s and T’s.

Rosalind Franklin 1950 X-Ray Diffraction

Clues from the X-Ray

– Coiled (forming Helix)

– Double-stranded

– Nitrogeneous bases are in the center

Watson & Crick

Francis Crick – British physicist

James Watson – American Biologist

– Building a 3D model of DNA

– Franklin’s X-Ray opened their eyes to the Double Helix

Watson and Crick’s model of DNA was a double helix, in which two strands were wound around each other.

Double Helix

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNA

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Questions

List the conclusions and explain how each of these scientists derived the conclusions:– Griffith– Avery– Hershey and Chase

Why did Hershey and Chase grow viruses in cultures that contained both radioactive phosphorus and radioactive sulfur? What might have happened if they only used one?

How did Watson and Crick’s model explain why there are equal amounts of thymine and adenine in DNA?

Interest Grabber

A Perfect Copy

When a cell divides, each daughter cell receives a complete set of chromosomes. This means that each new cell has a complete set of the DNA code. Before a cell can divide, the DNA must be copied so that there are two sets ready to be distributed to the new cells.

Section 12-2

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Interest Grabber continued

Section 12-2

1. On a sheet of paper, draw a curving or zig-zagging line that divides the paper into two halves. Vary the bends in the line as you draw it. Without tracing, copy the line on a second sheet of paper.

2. Hold the papers side by side, and compare the lines. Do they look the same?

3. Now, stack the papers, one on top of the other, and hold the papers up to the light. Are the lines the same?

4. How could you use the original paper to draw exact copies of the line without tracing it?

5. Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original?

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12–2 Chromosomes and DNA ReplicationA. DNA and Chromosomes

1. DNA Length

2. Chromosome Structure

B. DNA Replication

1. Duplicating DNA

2. How Replication Occurs

Section 12-2

Section Outline

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Chromosome

E. coli bacterium

Bases on the chromosome

Prokaryotic Chromosome Structure

Section 12-2

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•No Nucleus

Prokaryote DNA

Most have one circular chromosomeone circular chromosome located in the cytoplasm with some plasmids (circular DNA molecule found in bacteria) as well

– E.Coli (1.6μm diameter)– 4,639,221 base pairs 1.6mm long – Like packing 300m of rope in your backpack

Eukaryotes and DNA

1000 times more base pairs than bacterial DNA

Smallest human chromosome has 30 million base pairs of DNA

How do eukaryotes fit all that DNA in its nucleus?

Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

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DNA to Chromosomes

Vocabulary

– Chromatin - granular material (uncondensed) within the nucleus; consists of DNA tightly coiled around proteins

– Chromosomes – condensed chromatin

– Histone - globular protein molecule around which DNA is tightly coiled in chromatin

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, or model, for the new strand.

Enzymes unwind DNAEnzymes split “unzip” double

helixThe enzyme, DNA polymerase,DNA polymerase,

finds and attaches the corresponding N-base

Each “old” stand serves as a template and is matched up with a new stand of DNA

New helixes wind back up.

Figure 12–11 DNA Replication

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Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

DNA Replication

A – C – T – T – G – G – A – C

T – G – A – A – C – C – T - G

Interest Grabber

Information, Please

DNA contains the information that a cell needs to carry out all of its functions. In a way, DNA is like the cell’s encyclopedia. Suppose that you go to the library to do research for a science project. You find the information in an encyclopedia. You go to the desk to sign out the book, but the librarian informs you that this book is for reference only and may not be taken out.

Section 12-3

1. Why do you think the library holds some books for reference only?2. If you can’t borrow a book, how can you take home the information in it?3. All of the parts of a cell are controlled by the information in DNA, yet

DNA does not leave the nucleus. How do you think the information in DNA might get from the nucleus to the rest of the cell?

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12–3 RNA and Protein SynthesisA. The Structure of RNA

B. Types of RNA

C. Transcription

D. RNA Editing

E. The Genetic Code

F. Translation

G. The Roles of RNA and DNA

H. Genes and Proteins

Section 12-3

Section Outline

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from to to make up

Concept Map

Section 12-3

also called which functions to also called also called which functions towhich functions to

can be

RNA

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

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RNA and Protein Synthesis

Codon - three-nucleotide sequence on messenger RNA that codes for a single amino acid

Anticodon - group of three bases on a tRNA molecule that are complementary to an mRNA codon

Protein Synthesis: Two Parts

Transcription• Occurs in the nucleus• Formation of a single strand of messenger RNA from

DNA

Translation• Occurs on ribosomes• Cell uses the information on mRNA to assemble

amino acids in the proper order to form specific

proteins

Transcription

Occurs in nucleus

Enzymes unwind DNA

Enzymes split “unzip” double helix

RNA polymerase binds to promoter sequence (signal) on DNA

RNA polymerase transcribes a single strand of mRNA

RNADNA

RNApolymerase

Figure 12–14 Transcription

Section 12-3

Adenine (DNA and RNA)Cystosine (DNA and RNA)Guanine(DNA and RNA)Thymine (DNA only)Uracil (RNA only)

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Figure 12–17 The Genetic Code

Section 12-3

Proteins are made by joining amino acids into long chains

called polypeptides. Each polypeptide contains a

combination of any or all of the 20 different amino acids.

The genetic code shows the amino acid to which each of the

64 possible codons corresponds.

There is one codon, AUG, that can either specify methionine, or serve as the initiation, or “start”,

for protein synthesis.

There are three “stop” codons that do not code for any amino

acid.

Messenger RNA

Messenger RNA is transcribed in the nucleus.

Transfer RNA

The mRNA then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mRNA strand. The ribosome positions the start codon to attract its anticodon, which is part of the tRNA that binds methionine. The ribosome also binds the next codon and its anticodon.

mRNA Start codon

Ribosome

Methionine

Phenylalanine tRNALysine

Nucleus

Figure 12–18 Translation

Section 12-3

mRNA

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The Polypeptide “Assembly Line”The ribosome joins the two amino acids—methionine and phenylalanine—and breaks the bond between methionine and its tRNA. The tRNA floats away, allowing the ribosome to bind to another tRNA. The ribosome moves along the mRNA, binding new tRNA molecules and amino acids.

mRNARibosome

Translation direction

Lysine tRNA

tRNA

Ribosome

Growing polypeptide chain

mRNA

Completing the PolypeptideThe process continues until the ribosome reaches one of the three stop codons. The result is a growing polypeptide chain.

Figure 12–18 Translation (continued)

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Questions

1. What happens during DNA replication?

2. List and describe the three main types of RNA.

3. Describe the interactions between DNA, RNA, and

proteins during each part of protein synthesis?

4. Describe the main difference between RNA and

DNA.

Interest Grabber

Determining the Sequence of a Gene

DNA contains the code of instructions for cells. Sometimes, an error occurs when the code is copied. Such errors are called mutations.

Section 12-4

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Interest Grabber continued

Section 12-4

1. Copy the following information about Protein X: Methionine—Phenylalanine—Tryptophan—Asparagine—Isoleucine—STOP.

2. Use Figure 12–17 on page 303 in your textbook to determine one possible sequence of RNA to code for this information. Write this code below the description of Protein X. Below this, write the DNA code that would produce this RNA sequence.

3. Now, cause a mutation in the gene sequence that you just determined by deleting the fourth base in the DNA sequence. Write this new sequence.

4. Write the new RNA sequence that would be produced. Below that, write the amino acid sequence that would result from this mutation in your gene. Call this Protein Y.

5. Did this single deletion cause much change in your protein? Explain your answer.

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12–4 MutationsA. Gene Mutations

B. Chromosomal Mutations

Section 12-4

Section Outline

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Mutations

Mutation - change in a DNA sequence that affects genetic information

Two Main Types:

– Gene Mutation

• Mutation that causes a change in a single gene

– Chromosomal Mutation

• Mutation that causes a change in an entire chromosome

Substitution InsertionDeletion

Gene Mutations:Substitution, Insertion, and Deletion

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Gene Mutations

Point Mutation (substitution)– mutation that affects a single nucleotide, usually by

substituting one nucleotide for another

Frameshift Mutation (insertion or deletion)– mutation that shifts the “reading” frame of the genetic

message by inserting or deleting a nucleotide

Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

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Chromosomal mutations involve changes in whole chromosomes.

12–5 Gene RegulationA. Gene Regulation: An Example

B. Eukaryotic Gene Regulation

C. Regulation and Development

Section 12-5

Section Outline

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Interest Grabber

Regulation of Protein Synthesis

Every cell in your body, with the exception of gametes, or sex cells, contains a complete copy of your DNA. Why, then, are some cells nerve cells with dendrites and axons, while others are red blood cells that have lost their nuclei and are packed with hemoglobin? Why are cells so different in structure and function? If the characteristics of a cell depend upon the proteins that are synthesized, what does this tell you about protein synthesis? Work with a partner to discuss and answer the questions that follow.

Section 12-5

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Interest Grabber continued

Section 12-5

1. Do you think that cells produce all the proteins for which the DNA (genes) code? Why or why not? How do the proteins made affect the type and function of cells?

2. Consider what you now know about genes and protein synthesis. What might be some ways that a cell has control over the proteins it produces?

3. What type(s) of organic compounds are most likely the ones that help to regulate protein synthesis? Justify your answer.

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Regulatory sites

Promoter(RNA polymerase binding site)

Start transcription

DNA strand

Stop transcription

Typical Gene Structure

Section 12-5

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Regulatory site – places where other proteins, binding directly to the DNA sequences at those sites, can regulate transcription.

The actions of these proteins help to determine whether a gene is turned on or turned off.

Promoter - region of DNA that indicates to RNA polymerase where to bind to make RNA

Lac Operon (E. coli)

Operon – a group of genes that act together

Operator bound – RNA polymerase can’t transcribe genetic information (not expressed)

Operator free – gene(s) expressed

Operator - region of chromosome in an operon to which the repressor

binds when the operon is “turned off”

Eukaryotic Gene Regulation

mRNA editing before going to transcription

Intron - intervening sequence of DNA; does not code for a protein (not used)

Exon - expressed sequence of DNA; codes for a protein (used)

TATA box – a short region of DNA about 30 base pairs long; seems to help position RNA polymerase by marking a point just before the point at which transcription begins

Eukaryote Gene Regulation

DNA region about 30bp long TATATAAA: help to align RNA Polymerase

Genes are regulated in a variety of ways by enhancer sequences

Gene Regulation

Prokaryote Gene Regulation– Will often have one OPERATOR (regulatory site) controlling the expression

of more than one gene OPERON

Eukaryote Gene Regulation– Most eukaryotic genes are controlled individually and have regulatory

sequences that are much more complex than those of the lac operon

Gene Reg. and Development

hox genes - series of genes that controls the organs and tissues that develop in various parts of an embryo

Mutations affecting the hox genes in the fruit fly, Drosophila, for example, can replace the fly’s antennae with a pair of legs growing right out of its head!