Go to Section: Order! Genes are made of DNA, a large, complex molecule. DNA is composed of...

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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 each new 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 DNA

A.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

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1928-British scientist, F. Griffith, was studying two strains of bacteria that were associated with pneumonia

-one strain caused pneumonia (smooth)

-other strain was harmless (rough)

Initial experiment

a. inject mice with smooth strain-death

b. inject mice with rough strain-live

c. Inject mice with heat-killed smooth strain-live

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Second experimentmixed heat-killed, disease-causing bacteria with the live harmless bacteria-death- when he pulled fluids from the dead mice’s lungs he found living smooth bacteria.

Griffith’s hypothesis:transformation-process in which one strain of bacteria is changed by a gene or genes from another strain of bacteria

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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

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Figure 12–2 Griffith’s Experiment

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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

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Figure 12–2 Griffith’s Experiment

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1944-O. Avery repeated Griffith’s work to determine which molecule in the heat-killed bacteria was most important for transformation

Initial experiment-destroyed the proteins, lipids, carbohydrates, and RNA of the heat-killed bacteria with enzymes-transformation still takes place when added to harmless bacteria

Second experiment-used enzymes to break down the molecule DNA and then added to this to the harmless bacteria-no transformation

Conclusion: DNA stores and transmits genetic information from generation to generation.

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1952-Hershey and Chase designed an experiment to verify that genes were made of DNA using bacteriophages (viruses that attaches to bacteria, injects its DNA into the bacteria, and causes the bacteria to produce more viruses)

Grew virus cultures in radioactive isotopes that would mark either the protein coat or DNA.

Hershey and Chase concluded that the genetic material of the bacteriophage was DNA

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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

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Section 12-1

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Components and Structure of DNA1. Long molecule made of units called nucleotides

2. Nucleotides composed of:

a. Deoxyribose-5-carbon sugar

b. Phosphate group

c. Nitrogenous base

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Purines Pyrimidines

Adenine Guanine Cytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA Nucleotides

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Chargaff’s Rules

States that the percentage of guanine and cytosine present in DNA are equal and that adenine and thymine are also equal.

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Percentage of Bases in Four Organisms

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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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1950’s-X-ray evidence gathered by Franklin was used by Watson and Crick to further develop the double helix model of DNA in which two strands were wound around each other.

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Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–7 Structure of DNA

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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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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 Replication

A.DNA and Chromosomes

1. DNA Length

2. Chromosome Structure

B.DNA Replication

1. Duplicating DNA

2. How Replication Occurs

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Section Outline

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PROKARYOTES

Prokaryotic cells lack nuclei and membrane-bound organelles. Their DNA is located in the cytoplasm usually as a single circular DNA molecule that contains nearly all of the cell’s genetic information. This is the prokaryotic cell’s chromosome.

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Chromosome

E. coli bacterium

Bases on the chromosome

Prokaryotic Chromosome Structure

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EUKARYOTES

Eukaryotic cells can have up to 1000 times more DNA

DNA is generally found in nucleus in the form of a number of chromosomes

ex. Diploid human cells=46 chromosomes

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DNA Length

The relative length of DNA is very long. The chromosome of bacteria, E. coli, is 1.6 mm. This is 1000 times longer than the bacteria itself.

Chromosome Structure

The DNA in a Eukaryotic cell is packed even tighter. The nucleus of a human cell contains more than a meter of DNA!

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Figure 12-10 Chromosome Structure of Eukaryotes

Chromosome

Supercoils

Nucleosome

Histones

double

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DNA is tightly coiled around a protein called histones to form a substance called chromatin. Each histone molecule along with the DNA that is coiled around it is called a nucleosome. Nucleosomes enable cells to fold enormous lengths of DNA into the cell’s nucleus.

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DNA ReplicationBefore a cell divides it duplicates its DNA in a copying

process called replication. The DNA molecule separates into two strands, and then forms two new complementary strands following the base pair rules

Replication forks are the separation of the two strands of DNA that allow replication. These forks are created by an enzyme that “unzips” the DNA molecule. Another enzyme called DNA polymerase joins individual nucleotides to the two strands producing two identical DNA molecules.

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Figure 12–11 DNA Replication

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Growth

Replication fork

DNA polymerase

New strand

Original strand DNA

polymerase

Nitrogenous bases

Replication fork

Original strand

New strand

Video 2Video 2

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Information, PleaseDNA 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 Synthesis

A. 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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RNA and Protein Synthesis

Genes-sequence of DNA that codes for production of a protein thus determines a trait

This segment of DNA is copied into RNA and transferred outside of the nucleus to the site of protein synthesis.

Structure of RNA

RNA consists of a long chain of nucleotides, similar to DNA; however there are 3 main differences:

1. Ribose instead of Deoxyribose

2. RNA is generally single stranded

3. Uracil instead of Thymine

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Types of RNAThe main function of RNA is to control the assembly of amino acids into proteins- protein synthesis

3 Types of RNA:1. messenger RNA(mRNA)-carries instructions from the DNA to the rest of the cell2. ribosomal RNA(rRNA)-helps make up ribosomes along with several proteins3. transfer RNA(tRNA)- transfers each amino acid to the ribosome as coded by mRNA

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Transcription

This is when an RNA molecule is produced by copying part of the DNA strand into a complementary sequence of RNA. It is accomplished by an enzyme (RNA polymerase) binding to and separating the DNA strands. RNA polymerase then uses one strand of DNA as template to assemble the sequence of RNA.

promoters-site on DNA in which the enzymes will bind

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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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RNA Editing-

RNA molecules require editing before they leave the nucleus and are used to assemble proteins.

introns-sequences of nucleotides not involved in coding for proteins

exons-sequences that are expressed in protein synthesis

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The Genetic CodeProteins are made up of long chains of amino acids called polypeptides. The order in which these amino acids are assembled is determined by the order of the nucleotides on the strand of mRNA. During translation , the code is read three nucleotides at a time. This is known as a codon.

Example UCGCACGGU UCG-CAC-GGU serine-histidine-glycine

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Figure 12–17 The Genetic Code

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Translation

The decoding of an mRNA molecule into a polypeptide chain and ultimately a protein.

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Figure 12–18 Translation

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Figure 12–18 Translation (continued)

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from to to make up

Concept Map

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

can be

Messenger RNA Ribosomal RNA Transfer RNA

mRNA Carry instructions rRNACombine

with proteins tRNABring

amino acids toribosome

DNA Ribosome Ribosomes

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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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Figure 12–17 The Genetic Code

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12–4 Mutations

A.Kinds of Mutations

1. Gene Mutations

2. Chromosomal Mutations

B.Significance of Mutations

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Mutations are changes in the genetic material.

Point mutations -gene mutations involving changes in one or a few nucleotides. These include:

a. Substitutions

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Frameshift mutations -gene mutations in which one nucleotide change can alter the assembly of every amino acid that follows the point of the mutation.

a. Insertions

b. Deletions

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Substitution InsertionDeletion

Gene Mutations: Substitution, Insertion, and Deletion

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Section 12-4

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Chromosomal mutations - mutations that involve changes in the number or structure of chromosomes.4 types:

a. Deletionb. Duplicationc. Inversiond. Translocation

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Deletion

Duplication

Inversion

Translocation

Figure 12–20 Chromosomal Mutations

Section 12-4

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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?

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.

Go to Section: Order! Genes are made of DNA, a large, complex molecule. DNA is composed of...

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