Chapter 12: Chapter 12: DNA and RNADNA and RNASection 12-1: DNASection 12-1: DNA

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Interest GrabberInterest Grabber

Section 12-11. 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?

Section 1 AnswersSection 1 Answers

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.

•Order! Order!Order! Order!• Genes are made of DNA, a large, Genes are made of DNA, a large,

complex molecule. complex molecule.

• DNA is composed of individual units DNA is composed of individual units called nucleotides. called nucleotides.

• Three of these units form a code. Three of these units form a code.

• The order, or sequence, of a code and The order, or sequence, of a code and the type of code determine the the type of code determine the meaning of the message.meaning of the message.

Scientists Scientists wondered….wondered….

•What are What are genes ?genes ?

•What are What are they made they made of?of?

Genes…Genes…•How do they determine the How do they determine the

characteristics of critters? characteristics of critters? •Can we identify the Can we identify the

structure of the “gene” ?structure of the “gene” ?•Can we figure out how Can we figure out how

genes are inherited?genes are inherited?

Genes…Genes…•Are they single Are they single

molecules?molecules?•Are they long structures?Are they long structures?

• A. Griffith and TransformationA. Griffith and Transformation– 1. Griffiths Experiment1. Griffiths Experiment– 2. Transformation2. Transformation

• B. Avery and DNAB. Avery and DNA• C. The Hershey Chase ExperimentC. The Hershey Chase Experiment

– 1. Bacteriophages1. Bacteriophages– 2. Radioactive Markers2. Radioactive Markers

• D. The Components and Structure of D. The Components and Structure of DNADNA– 1. Chargaff’s Rules1. Chargaff’s Rules– 2. X-Ray Evidence2. X-Ray Evidence– 3. The Double Helix3. The Double Helix

DNA Scientists Video Clip

Let’s learn Let’s learn about the about the scientists scientists

involved in DNA involved in DNA research !research !

ScientistScientist ContributionContribution ConclusionConclusion

GriffithGriffith

AveryAvery

Hershey-ChaseHershey-Chase

FranklinFranklin

WilkinsWilkins

ChargaffChargaff

Watson-CrickWatson-Crick

BrennerBrenner

GilbertGilbert

A. Griffith and A. Griffith and TransformationTransformation

1. Griffiths Experiment1. Griffiths Experiment2. Transformation2. Transformation

1. Griffiths 1. Griffiths ExperimentExperiment1. Griffiths 1. Griffiths ExperimentExperiment

Griffith was looking for Griffith was looking for something other than something other than

a Gene !a Gene !

Frederick Frederick Griffith..Griffith..

• In 1928, In 1928, Griffith Griffith wondered wondered how bacteria how bacteria made people made people sick.sick.

This is the bacteria that causes pneumonia. Griffith was interested in how this happened.

Griffith isolated 2 Griffith isolated 2 strains of bacteria that strains of bacteria that

were easily were easily distinguisheddistinguished

•Disease Disease causing causing strain had strain had smooth smooth edgesedges

•Harmless Harmless strain had strain had rough edgesrough edges

ExperimentExperiment ResultsResults

SmoothSmooth

RoughRough

Heat killed Heat killed smoothsmooth

Heat killed Heat killed smooth + smooth + harmless roughharmless rough

Construct and Complete

How did this happen? How did this happen? Shouldn’t they have lived?Shouldn’t they have lived?

Something besides the pneumonia had caused the disease .. But what ?

Griffith decided..Griffith decided..•Something had Something had

caused the heat caused the heat killed bacteria to killed bacteria to pass on their pass on their disease causing disease causing ability to the ability to the harmless bacteriaharmless bacteria

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 Figure 12–2 Griffith’s 12–2 Griffith’s ExperimentExperiment

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 Figure 12–2 Griffith’s ExperimentExperiment

Griffith Griffith concluded..concluded..

•The heat killed bacteria The heat killed bacteria had somehow passed on had somehow passed on their disease causing their disease causing ability to the harmless ability to the harmless bacteria….bacteria….

2. Transformation2. Transformation

Griffith thought it Griffith thought it might be due to a might be due to a

gene !gene !

Griffiths last Griffiths last experimentexperiment

B. AveryB. Avery

Read about Griffiths Read about Griffiths work and wondered…work and wondered…

Avery Avery wondered…wondered…

•What caused the What caused the transformation ?transformation ?

So…So…•Avery decided to repeat Avery decided to repeat

Griffiths work to determine Griffiths work to determine which molecule had caused which molecule had caused the transformation … but the transformation … but with a different approach.with a different approach.

Avery …Avery …•Decided to Decided to destroy each destroy each

substancesubstance in the cells to in the cells to see which one see which one causedcaused the rough to transform the rough to transform into smooth.into smooth.

SubstanceSubstance Result in Result in mice ?mice ?

TransformatioTransformation factor ? Y/Nn factor ? Y/N

PolysaccharidePolysaccharidess

LipidsLipids

RNARNA

ProteinProtein

DNADNA

Avery’s Avery’s ExperimentExperiment

•If a substance was If a substance was destroyed and destroyed and transformation still occurstransformation still occurs, , then that substance then that substance couldn’t have caused couldn’t have caused transformation!transformation!

Which one Which one caused caused

transformation ?transformation ?

Avery realized…Avery realized…•The The

transformintransforming factor g factor must have must have been the been the DNA !DNA !

And that…And that…• DNA stores DNA stores

and transmits and transmits genetic genetic information information from one from one generation to generation to the next !the next !

C. The Hershey Chase C. The Hershey Chase ExperimentExperiment

1. 1. BacteriophagesBacteriophages2. Radioactive Markers2. Radioactive Markers

Martha Chase and Alfred Martha Chase and Alfred HersheyHershey

• Scientists like Scientists like Chase and Chase and Hershey are Hershey are skeptics !skeptics !

• They like to They like to test other test other peoples work !peoples work !

1. Bacteriophages1. Bacteriophages

Certain viruses…Certain viruses…•Attack bacteriaAttack bacteria•These are These are

called called bacteriophagesbacteriophages

BacteriophagesBacteriophages……

•They are composed of DNA They are composed of DNA or RNAor RNA

•The attach to the surface of The attach to the surface of a bacteria & inject their a bacteria & inject their DNA/RNADNA/RNA

Here are viruses Here are viruses that attack that attack

bacteriabacteria

HIV is a HIV is a retrovirusretrovirus

•It’s core is It’s core is RNA, not RNA, not DNADNA

•It infects It infects white blood white blood cellscells

2. Radioactive 2. Radioactive MarkersMarkers

Labelling DNA and Labelling DNA and proteinsproteins

Hershey & Hershey & Chase…Chase…

•Wondered which part of the Wondered which part of the virus infect the cell ?virus infect the cell ?

•Was it the Was it the proteinprotein or the or the DNADNA that caused that caused transformation ?transformation ?

The did this by….The did this by….•Labeling the protein with Labeling the protein with

3535S - a sulfur isotopeS - a sulfur isotope•And labeling the DNA And labeling the DNA

with with 3232P - a phosphorous P - a phosphorous isotopeisotope

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-Figure 12–4 Hershey-Chase ExperimentChase ExperimentSection 12-1

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Section 12-1

Figure 12–4 Hershey-Figure 12–4 Hershey-Chase ExperimentChase Experiment

Bacteriophage with phosphorus-32 in DNA

Phage infectsbacterium

Radioactivity inside bacterium

Bacteriophage with sulfur-35 in protein coat

Phage infectsbacterium

No radioactivity inside bacterium

Section 12-1

Figure 12–4 Hershey-Figure 12–4 Hershey-Chase ExperimentChase Experiment

Chase & Chase & Hershey..Hershey..

• They They concluded concluded that the that the material that material that caused caused transformatiotransformation was DNA!n was DNA!

But scientists weren’t But scientists weren’t yet satisfied !yet satisfied !

•How could genes carry How could genes carry information to the next information to the next generation ?generation ?

•How could genes “make” How could genes “make” the organism ?the organism ?

•How were genes copied ?How were genes copied ?

D. The Components and D. The Components and Structure of DNAStructure of DNA

1. Chargaff’s Rules1. Chargaff’s Rules2. X-Ray Evidence2. X-Ray Evidence

3. The Double Helix3. The Double Helix

DNA is made of DNA is made of nucleotidesnucleotides

Purines Pyrimidines

Adenine GuanineCytosine Thymine

Phosphate group Deoxyribose

Figure 12–5 DNA Figure 12–5 DNA NucleotidesNucleotidesSection 12-1

2 rings… 1 ring…

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–Figure 12–7 Structure of DNA7 Structure of DNA

Section 12-1

DNA BasesDNA Bases

1. Chargaff’s Rules1. Chargaff’s Rules

Nucleotide pairings…Nucleotide pairings…

Erin Chargaff…Erin Chargaff…•Discovered Discovered

the the percentages percentages of the basesof the bases

•Notice Notice that…that…

Percentage of Bases Percentage of Bases in Four Organismsin 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

2. X-Ray Evidence2. X-Ray Evidence

Franklin & WilkinsFranklin & Wilkins

Rosalind FranklinRosalind Franklin•Was an Was an

expert at X-expert at X-ray ray diffraction.diffraction.

X-ray images…X-ray images…• Of DNA were Of DNA were

created by beaming created by beaming x-rays at DNA and x-rays at DNA and recording the recording the imagesimages

• The X pattern The X pattern revealed the DNA revealed the DNA was a twisted helixwas a twisted helix

X-ray images…X-ray images…• The angle of the X The angle of the X

suggests that there suggests that there are 2 strandsare 2 strands

• The shape of the X The shape of the X also revealed that also revealed that the nitrogen bases the nitrogen bases were near the were near the center.center.

Maurice WilkinsMaurice Wilkins• Maurice also Maurice also

worked on x-worked on x-ray diffraction ray diffraction but with a but with a different different strand of DNAstrand of DNA

3. The Double Helix3. The Double Helix

The model builders…The model builders…

Watson & CrickWatson & Crick• Used the data Used the data

from Franklin’s from Franklin’s research to research to build several build several models of DNAmodels of DNA

• Their first Their first models were models were wrong.wrong.

This is Francis This is Francis Crick & James Crick & James

WatsonWatson• Their model Their model

explained explained how DNA how DNA could carry could carry information information and how it and how it could be could be copied.copied.

The DNA ModelThe DNA Model

DNADNA• Is a double Is a double

helixhelix• The 2 strands The 2 strands

wind around wind around each other.each other.

Hydrogen bonds

Nucleotide

Sugar-phosphate backbone

Key

Adenine (A)

Thymine (T)

Cytosine (C)

Guanine (G)

Figure 12–Figure 12–7 Structure of DNA7 Structure of DNA

Section 12-1