10 - recombination Flashcards
What are the 4 different types of recombination?
- homologous
- site-specific
- illegitimate
- transposition
What is transposition recombination?
when one transposon jumps from one location to the other or makes a copy and the copy jumps
what can recombination lead to?
- deletions
- insertions
- sequence duplication
- small changes - single base pair substitution
when does illegitimate recombination happen?
no homology
how does HIV use recombination?
- made from 2 RNA molecules
- recognised receptor on outside of cell and enters the cell and releases RNA
- RNA is reverse transcribed into double stranded DNA
- DNA enters nucleus via illegitimate recombination
-DNA is transcribed, more RNA is made - new viruses made
what is the process of HIV DNA entering the genome?
- viral ends resected to make 3’ overhang 2bp long
- host DNA strand cleaved 5pb apart
- viral strands ligates to cleaved ends by intergrase
- gaps are repaired by host enzymes
- can happen anywhere in the genome
what is an example onsite specific recombination?
phage lambda integrating into E. coli chromosome via site-specific recombination
What is the lytic cycle?
when a phage hijacks the cell to make more phages, cell the dies
What is the lysogenic cycle?
- when DNA is integrated into the host genome
What is a prophage?
bacterial cell that has a viral DNA in its genome
What is the process of the lytic cycle?
- phage attaches to host cell and injects DNA
- phage DNA circularises
- new phage DNA and proteins are made and viruses assembled
- cell lyses, releasing viruses
What is the process of the lysogenic cycle?
- phage attaches to host cell and injects DNA
- phage DNA circularises
- phage DNA integrates within bacterial chromosome
- cell is now a prophage
- bacteria reproduce
- sometimes bacterial will excise from chromosome and enter the lytic cycle
what is the details of site specific recombination?
- recombining molecules share a little homology
- ## either side of this is inverted repeats - recombination binding sites
Why is homologous recombination important?
genome stability
- repair of broken forks and DSBs
- accurate chromosome segregation in meiosis
genetic diversity
- meiotic and mitotic recombination of different alleles
- HGT in bacteria
Explain the process of homologous recombination
- DSB
- DSB resection- helicase and 5’-3’ exonuclease make 3’ overhangs
- strand invasion - 3’ overhang finds homologous chromosome and invades it via base pairing
- repair synthesis - DNA polymerase extends broken strand
- double holiday junction - repair is finished but connected by holiday junctions
- HJ resolution - can either have no cross over were 2 strands still contain original DNA or 2 stranded cross over
