final DNA recombination and transposons Flashcards
what do cells and organisms use homologous DNA recombination for
to fix, rearrange, or mutate their genomic DNA through strand invasion, branch migration, and DNA synthesis and repair
what do transposons do
they become parasites on genomic DNA and move from one place in the genome to another
how does the replication fork break
a nick in one of the strands of DNA is sufficient to break a replication fork if the nick is ahead of the replication fork
what are the steps of repair
- 5’ to 3’ degradation by an exonuclease
- invading 3’ end replaces a strand of double helix
- invasion is resolved by breaking a stand and by subsequent DNA synthesis to recreate fork
- replication proceeds as before
when does rapid zippering occur
when the correct base-pairing occurs and is then rapidly extended throughout the length of the DNA by zippering
what do RecA and Rad51 do
proteins that facilitate strand invasion (RecA uses ATP hydrolysis)
how do RecA and Rad51 work
during strand invasion, a single-strand of DNA has to displace a base-paired double helix. this requires energy and is promoted by RecA protein in E. coli and Rad51 in eukaryotes
what catalyzes directional branch migration
specialized helicases, which move branch point to allow longer strand to pair
what are the steps of homologoud recombination to repair double-stranded breaks
- the first step in homologous recombination is 5’ to 3’ degradation by an exonuclease at the double strand break region
- this generates free 3’ ends that can invade homologous DAN and through branch point migration result in the synthesis of new DNA
- strand invasion by any one free 3’ end is sufficient for homologous recombination to occur
what can crossover be generated by
homologous recombination in meiosis, programmed by double-stranded break
what can reversibly rearrange DNA
conservative site-specific recombination - the orientation of recognition sequences dictate type of reaction that occurs
what are transposable elements
jumping genes, which can move from one place in a gene to another
how do DNA-only transposons move
moves as DNA, either by cut-and-paste, where you cut out DNA, move to new spot, and insert, or replicative pathways, where copy of DNA Is inserted in new place
what does DNA-only transposons need for movement
transposase enzyme
how do retroviral-like-retrotransposons move
moves via an RNA intermediate (sequence in transcribed into RNA, which is reverse transcribed into DNA which is inserted into new place in chromosome - goes DNA to RNA to DNA)
