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

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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 Components and Structure of DNA

1. Chargaff’s Rules

2. X-Ray Evidence

3. The Double Helix

Section 12-1

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Disease-causing bacteria (smooth

colonies)

Harmless bacteria (rough colonies)

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

Control(no growth)



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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Goals

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Goals

To learn the relationship between genes and DNA

To learn the structure of DNA

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Many scientists tried to identify structures of genetic information to

understand how genes control inheritance.

Is there a molecule that carries the genetic code?

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Frederick Griffith

Originally, he was trying to determine the bacteria that caused

pneumonia

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Disease-causing bacteria (smooth

colonies)



Control(no growth)



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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Conclusion

One bacteria transformed into another.

The heat-killed bacteria passed their disease causing ability to the

harmless bacteria.

The disease causing ability?

A Gene

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Avery and other Scientists - 1944

Attempted to discover which molecule in the heat-killed bacteria

caused the transformation.

What substance made them (bacteria) change?

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The scientists made an extract of the heat-killed bacteria and subjected it to enzymes that destroyed proteins,

carbs, and lipids.

Transformation still occurred!

Obviously, proteins, carbs, and lipids were NOT involved with

transformation.

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Then Avery and his team subjected the extract to enzymes that would

break down DNA.

Transformation did NOT occur!

DNA was the transforming factor!!!

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Avery and others made a discovery…

DNA stores and transmits genetic information from one

generation to the next.

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The Hershey – Chase Experiment 1952

These scientists were skeptical about the results from Avery etal.

They designed an experiment to see if genes were actually made up of

proteins or DNA

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The Hershey – Chase Experiment 1952

They used bacteriophages and radioactive markers

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Bacteriophage

A virus that infects bacteria

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How does the virus function?

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Radioactive Markers

To determine if genes were actually made up of proteins or DNA, they

grew viruses in cultures containing radioactive isotopes

Phosphorous – 32 (32P)

Sulfur – 35 (35S)

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Radioactive Markers

Phosphorous – 32 (32P)

Sulfur – 35 (35S)

This was a clever strategy…

There is no phosphorous in protein, and no sulfur in DNA.

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There is no phosphorous in protein, and no sulfur in DNA.

Therefore, if 35S is found in the bacteria, the virus injected protein to

alter the cell.

If 32P is found in the bacteria, the virus injected DNA to alter the cell.

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Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat


No radioactivity inside bacterium

Figure 12–4 Hershey-Chase Experiment

Section 12-1

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Section 12-1


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Section 12-1


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The radioactive marked DNA was found in the bacteria cell.

ConclusionThe genetic material of the

bacteriophage was DNA, not protein.

In other words, genes are made from DNA.

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DNA Structure and Components

Read p. 291

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DNA

DNA is a very long molecule made up of nucleotides.

Nucleotides have three basic components:

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Phosphate Group

5 carbon sugar

Deoxyribose Nitrogenous base

Nucleotide

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DNA

There are four types of nucleotides based upon the nitrogenous bases.

Adenine - Thymine

Guanine - Cytosine

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DNA

The molecule is supported by a sugar-phosphate backbone.

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Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA Nucleotides

Section 12-1

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Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNA

Section 12-1

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Research that led scientists to discover the structure of DNA.

Chargaff’s Rules

Through intensive research he observed that for a variety of

organisms, there are near equal amounts of certain types of

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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The results from Chargaff’s research led scientists to

understand that

A-T and G-C

Chargaff’s Rules or Base Pairing

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X-ray Evidence

Rosalind Franklin used this special technique to show that the strands

of DNA are twisted around each other.

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The combination of Chargaff’s Rules and Franklin’s X-ray

diffraction led Watson and Crick to discovering the structure of DNA.

Nobel Peace Prize 1962Read p. 293

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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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Goals

What happens during

DNA Replication?

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Prokaryotic Cells

DNA is located in the cytoplasm

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Chromosome

E. coli bacterium

Bases on the chromosome

Prokaryotic Chromosome Structure

Section 12-2

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Eukaryotic Cells

DNA is located in the nucleus in the form of chromosomes

The number of chromosomes varies widely from one species to the next.

Human - 46 Fruit Fly - 8

Apes- 48Goldfish - 100 Corn - 20

Bread Wheat

42

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DNA Length

E. Coli – more than 4 million base pairs.

Highly coiled and folded, but when straightened, it can be as long as

1.6mm.

Human DNA is 1000x as longSee Fig. 12-9

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Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Coils

Nucleosome

Histones

DNA

double

helix

Section 12-2

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Duplicating DNA

DNA is replicated before the cell divides (which phase of the cell

cycle?)

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Figure 12–11 DNA Replication

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During DNA replication, the DNA molecule separates into two

strands.

Produces two NEW complementary strands following the rules of base

pairing. A – T and G - C

Each strand of the double helix of DNA serves as a template for the new

strand

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How Replication Occurs

1. Enzymes “unzip” the two strands.

The H bonds between the base pairs are broken and the two strands unwind.

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Section 12-2

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

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How Replication Occurs

2. New base pairs are added following the base pair rules.

DNA polymerase joins nucleotides to produce a new DNA molecule.

DNA polymerase also “proofreads” each new strand.

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Result

Each DNA molecule formed from replication has one original strand

and one NEW strand.

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Section 12-2

Growth

Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

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Sooooo What!?! Why is this important?

The reason that Watson and Crick’s discovery is so important is that they explained how DNA can be replicated.

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In other words, they helped explain how the GENETIC CODE can be copied and passed from generation to generation!!!

Sooooo What?!! Why is this important?

Read p. 297

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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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Goals

Recognize and learn three main types of RNA

Understand transcription

Understand translation

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RNA structure…

is similar to DNA

Nucleotides are the monomers (building blocks)

Five carbon sugar

Phosphate group

Nitrogenous bases

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DNA and RNA

Three Major Differences

DNA RNA

sugars

strands

Nitrogenous bases

Deoxyribose Ribose

Double Single

A T G C A U G C

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Three Types of RNA

In the majority of cells, most RNA molecules are involved in protein

synthesis.

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

mRNA Messenger RNA

Carries copies of the genetic information from the DNA to the

ribosomes.

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rRNA Ribosomal RNA

rRNA combines with proteins to make up ribosomes.

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tRNA Transfer RNA

Transfers a specific amino acid to the ribosomes during protein

synthesis.

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Transcription

“Re-writing” the code

Creating a copy of a DNA sequence into an mRNA sequence

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Figure 12–14 Transcription

Transcription

1. RNA polymerase separates DNA strands.

2. One of the DNA strands is used as a template to assemble an mRNA strand.

3. “Promoters” are used to start and stop the mRNA sequence.

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1. Where is DNA located in the eukaryotic cell?

2. Where does transcription take place?

3. Where does protein synthesis take place?

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Figure 12–17 The Genetic Code

The Genetic Code

The genetic code is the “language” of mRNA.

It is a code of three letters from an “alphabet” of four letters…

Codon – Three nucleotides (letters) that specify for a single amino acid

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AUG

CCC

UGG

GAGAGGUCC

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UCG CAC GGU

Serine Histidine Glycine

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Start Codon – signals for the beginning of protein synthesis.

AUG Methionine

Stop Codon – signals for the end of protein synthesis.

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A certain gene (DNA segment) has the following sequence of

nucleotides:

TACAAGTCCACAATC

From left to right, write the sequence of the mRNA molecule related to this gene. (What is this process called?)

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TACAAGTCCACAATC

AUGUUCAGGUGUUAG

Write the amino acid sequence of the polypeptide translated from the

mRNA.

Methionine (Start) – Phenylalanine – Arginine – Cysteine - Stop

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Translation

The decoding of an mRNA message into a polypeptide chain (protein)

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Figure 12–18 Translation

1. mRNA is transcribed from DNA in the nucleus

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2. mRNA goes to the ribosome.

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3. tRNA brings the proper amino acid to the ribosome.

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tRNA – a very special molecule

It is composed of a “loop” of RNA that has three exposed nitrogenous

bases.

anticodon

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The anticodon is complementary to a codon of mRNA

mRNA AUGUUCAGGUGUUAG

tRNA UACAAGUCCACAAUC

Each tRNA is specific for a certain amino acid

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A polypeptide chain (protein) is assembled using many amino acids.

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Figure 12–18 Translation (continued)

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Read p. 306

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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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RNADNA

RNApolymerase


Section 12-3


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Section 12-3

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Section 12-3

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Figure 12–18 Translation (continued)

Section 12-3

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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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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. Kinds of Mutations

1. Gene Mutations

2. Chromosomal Mutations

B. Significance of Mutations

Section 12-4

Section Outline

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http://www.youtube.com/

watch?v=D7IXiXxENEA

Mutant apples

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For pedicures, do they charge by the toe?

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Mutation -

Changes in genetic material

A mistake in DNA replication

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Two Types of Mutation

Gene Mutations

Chromosome Mutations

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Gene Mutations

Changes in a single gene

These mutations are also called point mutations …

… because they occur at a single point in the DNA sequence.

These mutations results in changes in one or a few nucleotides.

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Three Types of Gene Mutations

Substitutions, Insertions, and Deletions

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Substitution Mutations usually affect no more than a single amino acid

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Substitution InsertionDeletion

Gene Mutations: Substitution, Insertion, and Deletion

Section 12-4

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Insertions and Deletions

Changes in the DNA are more dramatic. Therefore these mutations can affect several amino acids.

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Insertion

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Deletion

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Chromosomal Mutations

These mutations changes the number and structure of chromosomes.

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Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Section 12-4

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Significance of Mutations

Most mutations are neutral…they do not disrupt biological activities

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Some mutations are harmful:

They can change protein structure or gene activity.

Genetic Disorders: cancer, sickle cell anemia

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Beneficial Mutations

May produce proteins with new activities that are useful in changing environments.

Adds to Genetic Variability!

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Read p. 308

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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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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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12–5 Gene RegulationA. Gene Regulation: An Example

B. Eukaryotic Gene Regulation

C. Development and Differentiation

Section 12-5

Section Outline

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Regulatory sites

Promoter(RNA polymerase binding site)

Start transcription

DNA strand

Stop transcription

Typical Gene Structure

Section 12-5

Videos

Click a hyperlink to choose a video.

Griffith’s Experiment

DNA Replication

DNA Transcription

Protein Synthesis

Duplication and Deletion

Translocation and Inversion

Point Mutations

Click the image to play the video segment.

Video 1

Griffith’s Experiment


Video 2

DNA Replication


Video 3

DNA Transcription


Video 4

Protein Synthesis


Video 5

Duplication and Deletion


Video 6

Translocation and Inversion


Video 7

Point Mutations

Interactive test

Articles on genetics

For links on DNA, go to www.SciLinks.org and enter the Web Code as follows: cbn-4121.

For links on DNA replication, go to www.SciLinks.org and enter Web Code as follows: cbn-4122.

For links on protein synthesis, go to www.SciLinks.org and enter the Web Code as follows: cbn-4123.

Go Online

http://www.scilinks.org/

Interest Grabber Answers

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

The units that make up cats are c, a, t, and s.

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.

Student codes may include: Act; Sat; Cat

3. Did any of the codes you formed have the same meaning?

No

4. How do you think changing the order of the nucleotides in the DNA codon changes the codon’s message?

Changing the order of the nucleotides changes the meaning of the codon.


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?Lines will likely look similar.

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

4. How could you use the original paper to draw exact copies of the line without tracing it?Possible answer: Cut along the line and use it as a template to draw the line on another sheet of paper.

5. Why is it important that the copies of DNA that are given to new daughter cells be exact copies of the original?Each cell must have the correct DNA, or the cell will not have the correct characteristics.


1. Why do you think the library holds some books for reference only?

Possible answers: The books are too valuable to risk loss or damage to them. The library wants to make sure the information is always available and not tied up by one person.

2. If you can’t borrow a book, how can you take home the information in it?

Students may suggest making a photocopy or taking notes.

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?

Students will likely say that the cell has some way to copy the information without damaging the DNA.


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.

Sequences may vary. One example follows: Protein X: mRNA: AUG-UUU-UGG-AAU-AUU-UGA; DNA: TAC-AAA-ACC-TTA-TAA-ACT

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.

(with deletion of 4th base U) DNA: TAC-AAA-CCT-TAT-AAA-CT

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.

mRNA: AUG-UUU-GGA-AUA-UUU-GA Codes for amino acid sequence: Methionine— Phenylalaine—Glycine—Isoleucine—Phenylalanine—?

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

Yes, Protein Y was entirely different from Protein X.


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?

Cells do not make all of the proteins for which they have genes (DNA). The structure and function of each cell are determined by the types of proteins present.

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?

There must be certain types of compounds that are involved in determining what types of mRNA transcripts are made and when this mRNA translates at the ribosome.

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

The type of compound responsible is probably a protein, specifically enzymes, because these catalyze the chemical reactions that take place.

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Documents

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