T.13 REPAIR-INDEPENDENT DNA RECOMBINATION Flashcards
(33 cards)
What is genetic recombination?
The process of genetic transmission derived from the reorganization of two DNA segments.
What are the main functions of genetic recombination?
Repair of homologous chromosomes during S phase, chromosome segregation, and providing genetic diversity.
What are the three types of genetic recombination?
Homologous recombination, non-homologous recombination, and within HR: site-specific and transposition recombination.
When does homologous recombination (HR) occur?
During meiosis in eukaryotes when homologous chromosomes are aligned on the equatorial axis.
What structure is involved in homologous recombination?
The chiasma.
What does homologous recombination involve?
Reorganization of long DNA segments between homologous chromosomes.
What are features of homologous recombination?
Requires homologous sequences; repairs DSB during end of S phase; increases genetic diversity during gametogenesis; no deletions or gene position changes.
What protein initiates HR in meiosis?
Spo11.
How does Spo11 act in homologous recombination?
Binds DNA through thyroxine, induces dsDNA cleavage, and creates 3’-stranded ends.
What happens after 3’ ends are formed in HR?
The largest strand migrates to the homologous chromosome to form recombinant DNA.
What enzyme joins the strands in HR?
DNA polymerase, without a primer.
How is the recombinant DNA resolved in HR?
Resolvase cuts the DNA in horizontal or vertical planes, forming a Holiday structure.
What is site-specific recombination?
A recombination mechanism that does not require homologous chromosomes, only short homologous points.
Which enzymes perform site-specific recombination?
Tyrosine recombinase and serine recombinase.
How do recombinases work in site-specific recombination?
They use their Tyr or Ser residues to bind DNA, cut one strand, and ligate it with another through nucleophilic attack.
What is the biological significance of site-specific recombination?
Important in genetic recombination during viral infection.
How do viruses use site-specific recombination?
They express their own recombinases to insert the viral genome into the host DNA.
Where can site-specific recombination occur?
In the same DNA strand or between different DNA strands.
What must be true for site-specific recombination to occur?
Strands must be oriented in the same direction.
What is inversion in site-specific recombination?
Occurs between strands originally in opposite directions that are reoriented in the same direction during recombination.
What is deletion and insertion in site-specific recombination?
Occurs between two recombinant sites of the same DNA strand in the same direction, forming a loop that deletes the middle sequence.
What is transposition?
A recombination mechanism using mobile genetic elements (transposons) that insert anywhere in the DNA without needing homology.
What is the function of transposition?
Genome structural organization, plasticity, gene expression modulation, and contributing to genetic diversity.
What are the two types of transposition systems?
DNA intermediates (transposons) and RNA intermediates (retrotransposons).
