Replication, Recombination and Repair Flashcards Preview

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Flashcards in Replication, Recombination and Repair Deck (98)
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1

What is recombination?

The shuffling of alleles between homologous chromosomes

2

What does recombination allow?

The selection of genes
A means of escape for favourable alleles and elimination for unfavourable alleles

3

Name 3 types of recombination

Homologous
Site specific
Transposition

4

What is homolgous recombination?

Responsible for meiotic crossing over and integration of transferred DNA into bacterial genomes

5

When does homologous replication occur in eukaryotes?

At the 4 strand stage of meiosis

6

What is the Holliday model?

A method of homologous recombination between double stranded DNA molecules with identical or nearly identical sequences.

7

What is the Holliday model applicable to?

Molecules with limited regions of homology or a single molecule with two separate regions of homology recombining with itself.

8

Describe the process of eukaryotic recombination.

Each sister chromatid contains duplex DNA
Homologous chromosomes pair and form bivalents
Pairing extends along chromosomes in the process of synapsis
Synaptonemal complex formed with homologous chromosomes side by side
Chromosomes separate but held together at chiasmata
Chromosomes condense, chiasmata remain, all 4 chromatids visible

9

Describe the Holliday model

Exchange of polynucleotides between 2 duplexes forms heteroduplex
Stabilised by base pairing between transferred strands
Gaps sealed by DNA ligase

10

What is resolution?

Spliced or patched
Cleaving across branchpoint reverts structure back into two individual double stranded DNA molecules

11

What is patched resolution?

A non-recombinant resolution due to cleavage in the same direction

12

What is spliced resolution?

A recombinant resolution due to cleavage in opposite directions

13

How does a hetroduplex region occur?

Two DNA molecules line up
Single stranded nicks appear at equivalent position in helix

14

What is the Meselson-Radding modification

Single-stranded nick in one helix which invades unbroken strand in the homologous position
Invasion produces D-loop
Cleavage of displaced strand generates heteroduplex

15

Where does recombination occur?

At double stranded breaks and single stranded gaps

16

Where do DSBs and SSGs come from?

DNA-damaging agents and normal DNA replication

17

What is the purpose of recombination?

Necessary to re initiate DNA replication
Repairs DSBs and rectifies aborted replication process

18

What does an exonuclease do in recombination?

Forms a double stranded break in the recipient strand
Digests 5' side of nick forming 3' overhang

19

What does RecA do?

Coats the 3'-ssDNA overhang

20

What are recombination specific helicases?

RecBCD and RecQ

21

What does RecBCD do?

Loads RecA protein onto overhang

22

What does RecQ do?

Works in conjunction with RecJ exonuclease to function at single stranded gaps

23

What happens when RecA fails to assemble?

RecF, RecO and RecR assemble

24

What is the presynaptic filament?

The nucleoprotein complex formed by the assembly of contigous RecA protein on ssDNA which undergoes homology search and strand invasion

25

What does the RuvAB complex do?

Branch migrates the crossover point

26

What does the RuvC protein do?

Holliday junction specific endonuclease which resolves the Holliday junction

27

What does the RuvABC complex do?

Recognises and cleaves the Holliday junction

28

What is oriC?

DNA replication in E.coli is origin dependent and must start from oriC

29

What is PriA?

A DNA replication protein that is required to reinitiate the replisome so Pol III can extend the nucleoprotein complex

30

What is gene conversion?

Distant markers from the crossover point are exchanged in a NON-reciprocal manner during recombination
One allele is converted to another with the exact base sequence represented at the converted site