Lecture 10 Flashcards
What are the functions of genetic recombination?
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
What are the three types of DNA recombination?
1) Homologous recombination
2) Site-specific recombination
3) Transpositional recombination
List the steps of homologous recombination
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
What complexes are involved in DSB-repair initiation?
RecBCD + RecFOR
What direction does RecB work?
3’ to 5’
What direction does RecD work?
5’ to 3’
What is the function of RecB?
It is the nuclease that is used during DSB repair initiation
What is the function of RecC?
It is involved in the binding of the the chi sequence
What is the function of both RecB and RecD
They are helicases
True or false: Chi sequences are symmetric
False, chi sequences are one-directional
What are the 3 steps to RecA mediated strand invasion?
1) Presynapsis
2) Synapsis
3) Postsynapsis (D loop formation)
What are the requirements to be a valid substrate for RecA strand exchange?
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
What is the function of RuvAB?
It helps with branch migration in holliday junctions
What is the function of RuvC?
It is the nuclease that cleaves specific DNA strands
Why is non-homologous end joining (NHEJ) more common in higher organisms?
NHEJ does not conserve the original sequence. Would be very bad for simpler organisms
What do double-strand breaks result from?
1) programmed breaks in meiosis
2) chemicals or radiation
3) meeting of a replisome and a single strand break in the template by replisome
What is genetic recombination?
It is the exchange of genetic information between chromosomes or different chromosomal segments in a single chromosome
What are the four possible outcomes when replisome meets an area of DNA damage in the template strand?
1) Translesion synthesis
2) Lesion bypass
3) Fork collapse
4) Stalled fork
What is the possible problem with using translesion synthesis?
It might cause a mutation
What is the mechanism used to fix a collapsed fork?
Replication reconstruction by recombination
What is the mechanism used to fix a stalled fork?
Replication restart by recombination
What is the mechanism used to fix a lesion bypass?
Gap repair by recombination
List the steps of replication reconstruction
1) 5’ end processing
2) Strand invasion
3) Branch migration
4) Holliday intermediate resolution and ligation
List the steps of replication restart
1) Fork regression
2) Either lesion repair or replication
3) Either digestion by nuclease or branch migration
4) Replication restart
List the steps of Gap repair
1) Strand invasion
2) Branch migration
3) Replication
4) Holliday intermediate resolution and ligation
