Lecture 10

Question 1

What are the functions of genetic recombination?

Answer 1

1) To establish genetic diversity
2) To separate deleterious mutations
3) To regulate the expression of certain genes
4) to knockout and edit genes
5) To repair double-stranded breaks

Question 2

What are the three types of DNA recombination?

Answer 2

1) Homologous recombination
2) Site-specific recombination
3) Transpositional recombination

Question 3

List the steps of homologous recombination

Answer 3

1) Double-strand break
2) End processing
3) First-strand invasion
4) Second-strand invasion
5) Strand extension
6) Use one of two pathways to complete repair

Question 4

What complexes are involved in DSB-repair initiation?

Answer 4

RecBCD + RecFOR

Question 5

What direction does RecB work?

Answer 5

3’ to 5’

Question 6

What direction does RecD work?

Answer 6

5’ to 3’

Question 7

What is the function of RecB?

Answer 7

It is the nuclease that is used during DSB repair initiation

Question 8

What is the function of RecC?

Answer 8

It is involved in the binding of the the chi sequence

Question 9

What is the function of both RecB and RecD

Answer 9

They are helicases

Question 10

True or false: Chi sequences are symmetric

Answer 10

False, chi sequences are one-directional

Question 11

What are the 3 steps to RecA mediated strand invasion?

Answer 11

1) Presynapsis
2) Synapsis
3) Postsynapsis (D loop formation)

Question 12

What are the requirements to be a valid substrate for RecA strand exchange?

Answer 12

1) one of the DNA molecules must have a single-stranded region
2) one of the molecules must have a free 3’ end
3) the above two features must occur in a region complementary between the two molecules

Question 13

What is the function of RuvAB?

Answer 13

It helps with branch migration in holliday junctions

Question 14

What is the function of RuvC?

Answer 14

It is the nuclease that cleaves specific DNA strands

Question 15

Why is non-homologous end joining (NHEJ) more common in higher organisms?

Answer 15

NHEJ does not conserve the original sequence. Would be very bad for simpler organisms

Question 16

What do double-strand breaks result from?

Answer 16

1) programmed breaks in meiosis
2) chemicals or radiation
3) meeting of a replisome and a single strand break in the template by replisome

Question 17

What is genetic recombination?

Answer 17

It is the exchange of genetic information between chromosomes or different chromosomal segments in a single chromosome

Question 18

What are the four possible outcomes when replisome meets an area of DNA damage in the template strand?

Answer 18

1) Translesion synthesis
2) Lesion bypass
3) Fork collapse
4) Stalled fork

Question 19

What is the possible problem with using translesion synthesis?

Answer 19

It might cause a mutation

Question 20

What is the mechanism used to fix a collapsed fork?

Answer 20

Replication reconstruction by recombination

Question 21

What is the mechanism used to fix a stalled fork?

Answer 21

Replication restart by recombination

Question 22

What is the mechanism used to fix a lesion bypass?

Answer 22

Gap repair by recombination

Question 23

List the steps of replication reconstruction

Answer 23

1) 5’ end processing
2) Strand invasion
3) Branch migration
4) Holliday intermediate resolution and ligation

Question 24

List the steps of replication restart

Answer 24

1) Fork regression
2) Either lesion repair or replication
3) Either digestion by nuclease or branch migration
4) Replication restart

Question 25

List the steps of Gap repair

Answer 25

1) Strand invasion
2) Branch migration
3) Replication
4) Holliday intermediate resolution and ligation