DNA Replication Machinery IV Flashcards
1
Q
Evidence to suggest coordination of leading and lagging strands
A
- looping of template for lagging strand
- topoisomerases
- processitivity
2
Q
Looping of template for lagging strand
A
enables dimeric replicative pol at replication fork to synthesise both daughter strands. leading and lagging strand pol complexes move along DNA in concert
3
Q
Topoisomerases
A
- produce transient ss or ds breaks in phosphodiester backbone of DNA
- action prevents accumulation of torsional strain in DNA
4
Q
DNA polymerases and processivity
A
- most core DNA polymerases only synthesise a short stretch of DNA before dissociating from DNA template
- clamp is required to increase processivity of polymerase
5
Q
PRO DNA Pol III E.Coli clamp; beta-subunit
A
- processivity of core enzyme of E.coli DNA Pol III is low (low tendency to remain on single template)
- formation of holoenzyme of DNA Pol III is completes by clamp (subunit beta)
- beta subunit makes holoenzyme highly processive
6
Q
EU PCNA clamp
A
- functions as trimer of timers
- similar to beta clamp
- form hexameric ring structure surrounding duplex
- sliding clamp that cannot fall off DNA
7
Q
How are PRO clamps loaded onto DNA
A
- beta-subunit ring of RNA Pol III is assembled around DNA by clamp loader complex
- clamp loaders form notched rings that bind and stabilise an open-ring state of a sliding clamp
8
Q
How are EU clamps loaded onto DNA
A
- PCNA is loaded onto DNA by RFC
9
Q
Replication at DNA ends
A
- telomers and telomerase
- loss of some sequences is compensated for by resynthesis of telomeric sequences by an enzyme called telomerase to extend 3’
10
Q
What is telomerase
A
- large ribo-nucleoprotein that includes RNA template and catalytic protein component
- reverse transcriptase
- present at ends of chromosome during G1 but only activated during S phase
- telomerase recognises the tip of existing telomere repeat sequence and elongates it
11
Q
Telomere shortening
A
- measure of the number of cell divisions
- link to cellular senescence
- link to cancer
