Biochemistry 3107: Week 4 Tutorial

1
Biochemistry 3107Week 4 Tutorial

• Phil Williams
• octobon_at_hotmail.com
• 777-6878
• HSC4333

2
Hershey-Delbruck Experiment

• E. coli was infected with two strains of
  bacteriophage T2.
• One strain is h-r
• One strain is hr-

3
Hershey-Delbruck Experiment

• h locus determines whether the phage can grow on
  a particular strain of E. coli
• phage that are h- can infect the strain
• phage that are h cannot infect the strain
• r locus is a gene that determines whether the
  phage will lyse the host cells rapidly or slowly
  
• phage that are r- will lyse the host cells
  rapidly
• phage that are r will lyse the host cell slowly

4
Hershey-Delbruck Experiment

• two strains of E. coli were used in the
  experiment
• strain 1 supports growth of h- phage but not h
  phage
• strain 2 supports the growth of both phage

5
Hershey-Delbruck Experiment

• Bacteriophage are plated on a lawn of bacteria
  that consists of a mixture of both strains of
  E. coli
• Expect two different phenotypes
• Both strains infected Clear plaques
• Infect only one of the two strains Turbid
  plaques

6
Hershey-Delbruck Experiment
7
Hershey-Delbruck Experiment Proves

• If an E. coli cell was infected at the same time
  with two genetically different bacteriophage,
  the resulting phage population included
  recombinant phage types as well as the original
  parental phage types
• The Nobel Prize in Physiology or Medicine 1969

8
Meselson-Weigle Experiment

• First demonstrated that both strands of each
  molecule must be broken and then rejoined in
  1961

9
Meselson-Weigle Experiment

• Infected E. coli cells at the same time with
  phage from two different stocks of
  bacteriophage lambda.
• Bacteriophage lambda c- mi-
• Heavy isotopes of carbon 13C and nitrogen 15N
• Bacteriophage lambda c mi
• Light isotopes of carbon and nitrogen

10
(No Transcript)
11
(No Transcript)
12
Meselson-Weigle Experiment

• Phenotypes of the intermediate density phage
  were recombinant phages
• c- mi found near the band of "heavy
  non- recombinant phage
• c mi- found near the band of "light"
  non- recombinant phage.

13
Meselson-Weigle Experiment

• These results can only be explained if
  recombination between the two parental phage
  involves breakage and rejoining of both DNA
  strands

14
Recombination Model
15
Recombination Model With Branch Migration
16
Holliday Model

• Holliday Model

17
Holliday Model
18
Double Strand Break Model
19
Double Strand Break Model
20
Double Strand Break Model
21
Question 16 On Midterm