Ch. 9 Notes DNA: The Genetic Material By: Brianna Shields December 8, 2005

Ch. 9 NotesDNA: The

Genetic MaterialBy: Brianna ShieldsDecember 8, 2005

DO NOW 1. Which scientist(s) “discovered”

transformation? 2. Hershey and Chase verified the

finding that what material is transferred during transformation?

3. What type of lab organism did Hershey and Chase use in their experiments?

List the terms in your vocab notebook, leaving about 3-4 spaces between each term

Vaccine Virulent Transformatio

n Bacteriophage Double Helix Nucleotide Deoxyribose

Base-pairing Rules

Complementary Base Pair

DNA Replication

DNA Helicase Replication

Fork DNA

Polymerase

GOALS

Relate Griffith’s conclusions to the observations he made during the transformation experiments

Summarize the steps involved in Avery’s transformation experimentsand state the results

Evaluate the results of the Hershey and Chase experiment Describe the three components of a nucleotide Develop a model of the structure of a DNA molecule Evaluate the contributions of Chargaff, Franklin and Wilkins in

helping Watson and Crick determine the double helical structure of DNA

Relate the role of the base pairing rules to the structure of DNA Summarize the process of DNA replication Describe how errors are connected during DNA replication Compare the number of replication forks in prokaryotic and

eukaryotic DNA

DNA: The Genetic Material

Griffith’s Experiment

Trying to develop a vaccine (killed/weakened bacteria or virus introduced to body to protect from future infection)



Two strains of streptococcus pneumoniae S - virulent (disease causing), has

capsule, grows in smooth colonies R- non disease causing, no capsule,

grows in rough colonies



1. Mice injected with S died

2. Mice injected with R were healthy



3. Was bacterial capsule causing death in mice?



4. Inject mice with dead S bacteria- mice remained healthy



5. Injected mice with heat killed S bacteria- (can’t reproduce but still have capsule)- mice lived



6. Injected mixed harmless live R with heat killed S into mice- mice died



7. Mouse blood contained R bacteria that had acquired capsules (somehow changed and became virulent S bacteria)

Discovered TRANSFORMATION

DNA: The Genetic Material Transforma

tion Change in genotype

caused when cells take in foreign genetic material


Avery’s Experiment

What substance is responsible for transformation?

Added protein destroying enzymes to heat killed S and healthy R mixture- transformation occurred

Added DNA destroying enzymes to same mixture- transformation stopped


Hershey and Chase Experiment

Wanted to confirm that DNA (not proteins) carried genetic material



Known facts A. Viruses made of DNA or RNA

surrounded by protective protein coat



Known facts B. Bacteriophages (viruses) infecxt

bacteria to produce more viruses (released when bacteria host ruptures)



Known facts C. Only DNA in phage contained

phosphorus D. Only protein coat in phage

contained sulfur



1. Grew a sample of T2 bacteriophage in radioactive sulfur medium (would be used in T2’s protein coat)



2. Grew a sample of T2 bacteriophage in radioactive phosphorus medium (would be used in T2’s DNA)



3. Allowed S and P labeled phages to infect E. coli bacteria Can detect radioactive S and P to

see if DNA, protein or both are transferred to E. coli



4. S and P phages removed from bacteria using blender

5. Centifuge spins heavy bacteria to bottom and light phages to liquidy top of mixture



6. Findings: A. S label found only in phages

(protein never injected into E. coli) B. P label found mostly in bacteria

(DNA transferred to E. coli) C. New generation of phages from

bursted bacteria also contained radioactive DNA



7. Conclusion: DNA is transferred from virus to

bacteria Protein remains outside cell DNA must be hereditary material

(atleast in viruses)

Assessment One Summarize Griffith’s transformation

experiments Describe how Avery’s experiment supplied

evidence that DNA, not protein is the genetic material

Describe the contributions of Hershey and Chase to the understanding that DNA is the genetic material

Why did heat kill Griffith’s S bacteria? What might Hershey and Chase have concluded

if they had found P and S in the bacteria cells?


Watson and Crick

Established the structure of DNA

Made a tin and wire model of DNA


Structure of DNA

1. Double helix- 2 strands of linked nucleotides twisted around like a winding staircase


Structure of DNA

2. Nucleotides- subunits that make up DNA, composed of: Phosphate group Five carbon sugar molecule (deoxyribose) Nitrogen containing base (four kinds)

Adenine Guanine Thymine Cytosine

Bases pair up to create” ladder rungs”


Structure of DNA

3. Base classification Purines- double ring of C and N

atoms Adenine and Guanine

Pyrimidines- single ring of C and N atoms

Thymine and Cytosine


Structure of DNA

4. Helix held together by weak hydrogen bonds between paired bases


Chargaff Discovered base pairing rule Amounts of adenine and thymine in

DNA are always the same Amounts of cytosine and guanine

in DNA are always the same Amounts of A and T, and G and C

differ


Wilkins and Franklins Photographs

Bounced X rays off DNA to create pattern scattered onto film

Photos indicate DNA is a tightly coiled helix with 2 chains of nucleotides


Pairing between bases

Because of size and structure of bases, only certain ones pair up to hold DNA together Adenine - Thymine Guanine - Cytosine


Pairing between bases

Results in complementary base pairs

Sequence on one strand of DNA can determine sequence of other strand

Assessment Two Describe the three parts of a DNA molecule Relate the base pairing rules to the structure of

the DNA Describe the two pieces of information from

other scientists that enabled Watsons and Crick to discover the double helical structure of DNA

Explain why the two strands of the double helix are described as complementary

What would be the complementary strand to DNA with the following base sequence: AGCTTAGTCA


Replication of DNA

Making a copy of DNA Complementary strands

of DNA serve as template for replicating DNA

Occurs during S phase of cell cycle (before division)


Replication of DNA

Steps: A. DNA helicase unwinds and

opens DNA by breaking H bonds between bases


Replication of DNA

Steps: B. Helix separates at replication

forks (Y shape), proteins attach to DNA and hold helix open


Replication of DNA

Steps: C. DNA polymerase enters fork,

moves along DNA strand adding nucleotides to exposed bases according to pairing rule

Proofreads, removes and fixes any mismatched nucleotides

Reduces error to 1 in a billion


Replication of DNA

Steps: D. DNA polymerase continues until

DNA is copied, then it is signaled to detach


Replication of DNA

Result: 2 new DNA double helices created (identical to each other and original DNA)


Rate of DNA replication

In circular prokaryotic DNA 2 replication forks that move away

from one another until they meet on other side of DNA circle


Rate of DNA replication

In eukaryotic DNA End o end replication would take a

month for one strand of DNA Have multiple replication forks so

several DNA portions are replicated simultaneously

One human chromosome takes 8 hours

Assessment Three Explain the two roles that enzymes play in DNA

replication Explain the relationship between DNA

polymerases and mutation State the effect of multiple replication forks on

the speed of replication in eukaryotes If a mutation occurs during the formation of an

egg cell or sperm cell, is that mutation more significant or less significant than a mutation that occurs in a body cell?

Websites Gene Scene DNA Workshop The Geee! In Genome Putting DNA to work Kids Genetics: DNA Hershey and Chase Experiment Animation DNA Replication Animation Another DNA Replication Animation

Documents

Ch. 9 Notes DNA: The Genetic Material By: Brianna Shields December 8, 2005