Lecture 6

Question 1

What must recombination involve?

Answer 1

Breakage and rejoining of DNA

Question 2

What are the steps of Holliday’s recomb model?

Answer 2

1. Alignment of DNA sequences
2. Break in 1 stand of each chromosome
3. Holliday junction formed by rejoining of DNA
4. Branch migration forms a heteroduplex region
5. Resolution regenerates separate chromosomes

Question 3

What is a heteroduplex region?

Answer 3

A double stranded DNA molecule but each strand is derived form a different parent molecule

Question 4

In the process of resolution, what are the two possible cut directions and products of these?

Answer 4

1. Horizontal cut -> heteroduplexes with NO recombinants

2. Vertical cut -> heteroduplexes WITH recombinants

Question 5

What are the steps of the modern recomb model?

Answer 5

1. Double stranded break, both strands on the SAME chromosome (different to Holliday’s model)
2. Erosion degrades DNA , leaving part of the DNA single stranded (Key difference to Holliday’s model)
3. Invasion and displacement (strand invasion). One strand displaces part of the other and becomes base paired forming a heteroduplex structure
4. Polymerisation occurs and DNA synthesis forms a double stranded molecule. The displaced DNA uses the past DNA strand as a template to pair. A Holliday junction forms
5. Resolution occurs and recombinants are formed

Question 6

How is double strand break repair similar to recombination?

Answer 6

A double stranded break 
Degradation of DNA strands 
Strand invasion, DNA synthesis 
Holliday junction formation 
Resolution can lead to cross over

Question 7

TRUE/FALSE

Bacteria are diploid

Answer 7

FALSE

Bacteria is haploid

Question 8

How do bacteria replicate?

Answer 8

Clonally

Question 9

How many chromosomes do bacterial cells have and what shape is it?

Answer 9

1x per cell, circular