8 chapter from dna to proteins - houghton mifflin...

CHAPTER

8 From DNA to Proteins

Preview Key Concepts 8.1 IdentifyingDNAastheGeneticMaterial

DNA was identified as the genetic material through a series of experiments.

8.2 StructureofDNADNA structure is the same in all organisms.

8.3 DNAReplicationDNA replication copies the genetic information of a cell.

8.4 TranscriptionTranscription converts a gene into a single-stranded RNA molecule.

8.5 TranslationTranslation converts an mRNA message into a polypeptide, or protein.

8.6 GeneExpressionandRegulationGene expression is carefully regulated in both prokaryotic and eukaryotic cells.

8.7 MutationsMutations are changes in DNA that may or may not affect phenotype.

Review Academic VocabularyWrite the correct word for each definition.enzyme ribosome protein

1. : biological catalyst

2. : site of protein synthesis

3. : shape determines its function

Preview Biology VocabularySee how many key terms from this chapter you already know. Rewrite each phrase, using a different word or words for the wordsinbold.

PhRASE REwRITTENwIThDIffERENTwoRDS

1. DNA replication allows every new cell to have a complete set of DNA.

DNA allows every new cell to have a complete set of DNA.

2. Mutagens such as UV light can result in skin cancer.

such as UV light

can result in skin cancer.

3. RNA is found in both the nucleus and the cytoplasm.

is found in both the nucleus and the cytoplasm.

GettinG ReAdy to LeARn

122

enzyme

ribosome

protein

copying

agents that cause changes to DNA

a type of single-stranded nucleic acid

BI_CNLEIR687797_C08.indd 122 4/13/11 11:20:10 AM

Identifying DNA as the Genetic MaterialKEyConCEPT DNA was identified as the genetic material through a series of experiments.

DNA was identified as the genetic material relatively recently—in the 1950s. This section reviews three research projects that all added up to this discovery: 1) Griffith’s research, 2) Avery’s research, and 3) Hershey and Chase’s research. Together, these scientists’ findings led to the con-clusion that DNA is the genetic material.

Griffithfindsa“transformingprinciple.”In 1928 a British microbiologist named Frederick Griffith investigated two forms of the bacterium that causes pneumonia*. He injected the two different forms into mice. One form of the bacterium killed the mice, but the other form did not.

Griffith used heat to kill a sample of the deadly disease-causing bacteria and then mixed the dead bacteria with a sample of live, harmless bacteria. He injected this mixture into mice. Even though the disease-causing bacteria that he injected were heat-killed, the mice still died.

Griffith concluded that some material must have been transferred from the heat-killed bacteria to the harmless bacteria. Whatever that material was, it con-tained information that changed the harmless bacteria into disease-causing bacteria. Griffith called this mys-tery material the “transforming principle.”

Transform means “to change.” Why do you think Griffith called the mystery material the “transforming principle”?

SEcTIoN

8.1

live S bacteria

liveR bacteria

heat-killed S bacteria

heat-killed S bacteria + live R bacteria

dead mouse dead mouse live mouse live mouse

live S bacteria

liveR bacteria




live S bacteria

liveR bacteria




TheSformofthebacteriumisdeadly;theRformisnot.

GRiffiTH’SExPERimEnTS

* AcADemic VocAbUlARy

pneumonia a disease that affects the lungs

Interactive Reader 123

changed, or transformed, the harmless bacteria into

deadly bacteria.

Because the material

> Virginia standards

BIO.1 The student will demonstrate an understanding of scientific reasoning, logic, and the nature of science by planning and conducting investigations.BIO.1.EKS-23; BIO.5.EKS-11


DNA

protein coat

AveryidentifiesDnAasthetransformingprinciple.

Oswald Avery worked with other biologists for over ten years trying to figure out what Griffith’s transforming principle was. They thought the transforming principle could be protein or it could be DNA. Avery’s group found a way to separate this mystery material from samples of bacteria. They ran several tests on the material. Their tests and findings are shown in the chart below.

AvERy’SRESEARCH

TEST RESULT

1. Standard chemical test for protein and DNA found presence of DNA, but no protein

2. Tests to determine the amounts of nitrogen (N) and phosphorous (P)

the proportions of N and P matched the makeup of DNA, but not protein

3. Tests to see which enzymes could break down the substance

enzymes that break down DNA broke down this substance, but enzymes that break down protein did not break down the substance

Avery and his group concluded that DNA must be the transforming principle, or genetic material. Some scientists questioned this conclu-sion. Scientists also wondered whether DNA was the genetic material for all organisms or just for bacteria.

on the chart above, highlight three reasons Avery concluded that the mystery material was DNA, not protein.

HersheyandChaseconfirmthatDnAisthegeneticmaterial.

In 1952 the work of Alfred Hershey and Martha Chase provided evi-dence that DNA is indeed the genetic material. Hershey and Chase studied a type of virus that infects bacteria, called a bacteriophage (bak-TEER-ee-uh-fayj), or “phage” for short.

A phage infects a bacterium by inserting its genetic material into the bacterium. Hershey and Chase wanted to find out what material the phage inserted into a bacterium—was it protein or was it DNA? They conducted two experiments. In the first experiment, Hershey and Chase marked the phages’ proteins with radioactive labels. When the phages infected the bacteria, no significant radioactivity was found inside the bacteria. In the second experiment, Hershey and Chase marked the phages’ DNA with radioactive labels. When the phages infected the

Bacteriophages are viruses that infect bacteria.

McDougal Littell Biology124


bacteria, high levels of radioactivity were found inside the bacteria. These results finally convinced scientists that the genetic material is DNA and not protein.

What is the material that phages insert into bacteria?

bacteriophage

1. How did Hershey and Chase’s research with bacteriophages help con-firm that DNA is the genetic material?

2. Complete the following chart about the three main research projects that led to the identification of DNA as the genetic material.

RESEARCHERS’nAmES SUmmARyofRESEARCH SUmmARyofConCLUSionS

Griffith found a “transforming principle”

Avery

hersheyandchase identified the substance that phages inject into bacteria

3. Which of the three experiments gave evidence that protein was not the genetic material?

8.1 vocabularyCheck

Go back and highlight each sentence that has a vocabulary word in bold.

Mark It Up

8.1 TheBigPicture


DNA

Because they are made of protein and DNA,

and Hershey and Chase found that the DNA was the part of the phage that was injected to spread the virus-and therefore contained genetic material.

used harmless and deadly pneumonia bacteria

did a variety of tests on samples of genetic material that they isolated

from bacteria

found that the material was DNA, not protein

confirmed that DNA, not protein is the genetic material

Avery’s and Hershey and Chase’s experiments


SEcTIoN

8.2DnAiscomposedoffourtypesofnucleotides.

Since the 1920s scientists have known the chemical parts of the DNA molecule. DNA is a very long polymer, or chain of repeating units. The units, or monomers, that make up DNA are called nucleotides (NOO-klee-oh-tydz). Each nucleotide has three parts: a phosphate group, a base, and a sugar.

There are four different types of DNA nucleotides: cyto-sine (C), thymine (T), adenine (A), and guanine (G). All of the nucleotides contain a phosphate group and a deoxyribose sugar. They differ in their nitrogen-containing bases, as shown in the table below.

Notice that thymine (T) and cytosine (C) have nitrogen-containing bases with a single-ring structure. Adenine (A) and guanine (G) are bases with a double-ring structure. A single molecule of human DNA is made of billions of nucleotides.

THEfoURniTRoGEn-ConTAininGBASESofDnA

PyRimiDinES=SinGLERinG PURinES=DoUBLERinG

NameofBase Structuralformula Model NameofBase Structuralformula Model

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

N

NH2

NH

C

C

C

HN

HC N

C O

C A

G

T

C

N

NH2

NH

C C C

C C

C

C

C

CH CH N N N N

HN HN

HN

NH NH

NH NH

HC HC

HC

N N

N

NH2 NH2

C C

C C

NH NH C C

HC HC

HC HC

HC HC

C C C CH3

O O

C C O O

O O

N N

NH2 NH2

C O

thymine

cytosine

adenine

guanine

circle the names of the four nucleotides shown in the table above.

Structure of DNAKEyConCEPT DNA structure is the same in all organisms.

The small units, or monomers, that make up a strand of DNA are called nucleotides.Nucleotides have three parts.

VISUALVOCAB

nitrogen-containingbase

phosphategroup

deoxyribose(sugar)

• phosphate group: one phosphorus with four oxygens

• deoxyribose: ring-shaped sugar• nitrogen-containing base: a single

or double ring built around nitrogen atoms and carbon atoms


> Virginia standards

BIO.5.e The student will investigate and understand common mechanisms of inheritance and protein synthesis. Key concepts include historical development of the structural model of DNA.BIO.1.EKS-23; BIO.5.EKS-11; BIO.5.EKS-12


* AcADemic VocAbUlARy

accurate correct

WatsonandCrickdevelopedanaccurate*modelofDnA’sthree-dimensionalstructure.

For a long time, scientists hypothesized that DNA in all organisms was made up of equal amounts of the four nucleotides. Then Erwin Chargaff found that the proportion of the bases differs from organism to organ-ism. In the DNA of each organism, the amount of A equals the amount of T, and the amount of C equals the amount of G.

Then in the early 1950s, the scientists Rosalind Franklin and Maurice Wilkins used x-rays to make a kind of photograph of DNA molecules. These photographs did not show what DNA looks like, but they showed patterns that gave clues about DNA’s structure.

Around the same time, the scientists James Watson and Francis Crick were working together to figure out DNA struc-ture, too. Based on the work of other scientists, they hypoth-esized that DNA might have a spiral, or helix (HEE-lihks), shape. Watson and Crick saw Franklin’s photos and used the information to complete their model of DNA structure.

In April 1953 Watson and Crick published their DNA model in a paper in the journal Nature. They found that nucleotides fit together in a double helix. Two strands of DNA wrap around each other like a twisted ladder.

What new information did Watson and crick contrib-ute to science?

nucleotidesalwayspairinthesameway.Each side of the DNA double helix is a long strand of phosphates and sugars, connected by covalent bonds. The two sides of the double helix are held to each other by hydrogen bonds that form between the bases in the middle. Each individual hydrogen bond is weak, but together they are strong enough to hold the shape of DNA. The bases of the two DNA strands always bond according to the base pairing rules: T pairs with A, and C pairs with G.

The bases pair in this way because of hydrogen bonds. Notice that A and T form two hydrogen bonds, whereas C and G form three.

To help remember the rules of base pairing, notice that the letters G and C have a similar shape. Once you know that G and C pair together, you know that A and T also pair together. If the sequence of bases on one DNA strand is CTGA, the other DNA strand will be GACT.

Watson and Crick’s model showed DNA in the shape of a double helix.


the three-dimensional shape of DNA-

a double helix


DG

GC

T

T

A

A

G

T

T

A

A

G

G

G

T

T

A

A

G C

C

C

C

G C

C

C

D

D

D

D

DD

D

D

D

DD

D

DD

D

D

D

DD

DD

P

PP

P P

P

P

PP

P

P

P

P

P

P

P P

P

P

P

P

P

P

P

P

P

P

P

D

D

D

D

D

D

D

D

D

BASEPAiRinGRULES

ThebasepairingrulesdescribehownucleotidesformpairsinDnA.TalwayspairswithA,andGalwayspairswithC.

A

G

T

C

T

C

A

G

hydrogenbond covalentbond

G c

A T

Gc

T A

The nitrogen-con-taining bases bond in the middle to form the rungs of the DNA ladder.

This ribbonlike part represents the phos-phategroups and deoxyribosesugar mol-ecules that make up DNA’s “backbone.”

What sequence of bases would pair with GTAcG?

nucleotide base pairing rules

double helix

1. Label the drawing at the right with the terms nucleotide, base pairing rules, and double helix. Write each term and draw a line that connects the term to the appropriate part of the drawing.

2. What are the three different parts of a nucleotide?

3. What are the names of the four nucleotides?

4. Use the base pairing rules to write the sequence that would pair with the following sequence: TCACGTA

8.2 vocabularyCheck

Go back and highlight each sentence that has a vocabulary word in bold.

Mark It Up

8.2 TheBigPicture


CATGC

Double Helix

phosphate group,

deoxyribose (sugar), and a nitrogen-containing base

adenine, cytosine, guanine, and

thymine

AGTGCAT

nucleotide

base pairing rules


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