DNA replication Flashcards
DNA topoisomerase
Relieves the tension in DNA
Ribonuclease
Degrades RNA primers
Telomerase
Replicates the ends of the chromosome
DNA unwinding
1) DNA helicase: Unwinds DNA using ATP to propel itself across the DNA
2) SSB: Binds and keeps strands apart
3) DNA topoisomerase: relieves tension
DNA synthesis
1) DNA polymerase needs template
2) DNA polymerase requires a primer
3) Always in 5’ to 3’ direction
What is a primer?
Short segment of RNA complementary to the template with a 3’ OH
Lagging Strand
-DNA primase: attaches RNA to template
-DNA polymerase III: adds nucleotides until reaches previous primer
-RNase H: digests the RNA primer; leaves a gap
-DNA polymerase I: fills in gaps
-DNA ligase: joins Okazaki fragments together
Telomeres
Repetitive regions at end of chromosomes
Act as caps to protect internal regions of chromosomes; worn down in DNA replication
Problem with telomeres
Part of DNA at end of chromosomes goes uncopied each round of replication
Chromosomes get shorter and shorter
Telomeres solution
-Enzyme telomerase; can make DNA from using RNA as a template
- Binds to RNA molecule containing sequence complementary to telomeric repeat
- Recognises tip of repeat sequence and uses RNA to add additional repeats to telomere DNA
Depurination
No DNA breaks
Removal of purines (Guanine and Adenine)
Deamination
No DNA breaks
Results in C to U transition
Thymine dimers
Caused by UV light exposure
2 adjacent thymine bases become covalently bonded
Stalls replication machinery
Nonsense mediated decay
During translation transcripts with premature stop codons are detected and degraded
Mechanisms for DNA repair
-Excision: recognition and removal of damage using exonuclease
-Repair: re-synthesis of missing DNA using DNA polymerase
-Joining: sealing the gap using DNA ligase
