Oct 25 Flashcards
How does non-homologous end joining work, when occur? Do you get mutations from this?
It is when sister chromosome not available to invade to use as a template. It will have ds break, then Ku70/80 will bind on each end, recruit other proteins to join the strands, can get indels if break happens before DNA replication, as during break can get indels put in
How does repair by translesion DNA synthesis work?
It works by DNA pol 3 stalling at lesion in replication fork. Then it leaves and polymerase of Y family is recruited, it has less proofreading ability, is less picky. Once it synthesizes past the lesion, then pol 3 will take over again. Mutations produced, but cell doesn’t die
What are the 2 major purposes of homologous recombination?
- To get new genetic diversity from crossing over
- To fix SSB and DSB
What 4 things can cause DSBs?
When replication forks encounter SSB in template strand, meiotic recombination, UV light/radiation, oxidative DNA damage
What happens during lesion bypass?
The leading strand will stall, the lagging strand will keep going, so ss break happens on new strand, just gets skipped.
How is a chromosomal DSB repaired?
Exonuclase creates 3’ overhands by degrading the 5’ ends
2. The 3’ end invades with recombinase helping to form displacement (D-loop).
3.The D loop is expanded when the 5’ end of that same strand as the 3’ will invade, so now the D loop completely fills that gap on the broken chromosome. Now the nonbroken chromosome is used as template to repair broken chromosome
What is the synthesis-dependent strand annealing pathway?
It is when strands dissociate following invasion, then become like they once were, so all parental DNA together and all of the other sister chromosome is intact
What is the DSB repair pathway during DSP repair?
It is when 2 holliday intermediates, the intermediate resolvases cut the intermediates and can get actual crossing over or not.
How does recombinational DSB reapir at collapsed replication fork occur?
- When template has a break, it will stall synthesis at that spot, therefore you now have DS break and fork collapse.
2.The broken DS end has the 5’ end part removed of the template strand, so the new strand has 3’ overhang. - Recombinase will hep the 3’ overhand invade the its complementary strand on the other side of the replication bubble.
- Branch migration occurs, the 5’ end of the broken bit invades too
Then resolution of holiday juncctions
What is branch migration?
It is movement of the crossed branch point, the net amount of duplex DNA stays same, the x formed between the 2 pairs of DNA just moves
What happens when branch migration triggers fork regression?
1.If stalling occurs, then the fork regresses (parental strands reanneal), and the new strands that were made do a U turn as the fork closes a bit.
Then 2 things can happen:
1.The digestion enzymes get rid of the bit of strands that U-turned, then replication can continue once the lesion is repaired
OR
2. The new strands that u turn, one of them that stalled is shorter, so it is lengthened so same length as new strand using the other new strand as a template, then they u turn again and this way it passes the lesion, can repair it later
What are the 4 “tene”s of prophase, what happens in each?
- Lepto = Chromosomela condensation
- Zygo = homologous chromosomes pair (synapsis), crossing over occurs
- Pachy = Synapsis finished
- Diplotene = the synaptonmeal complex disappears, chromosomes start moving apart
What are chiasmata?
They are the remaining points of attachment between homologous chromosomes.
