lec 5. DNA replication Flashcards
enzymes used in DNA replication
helicase DNA primase DNA polymerase ε (leading strand) DNA polymerase δ (lagging strand) Ribonuclease H DNA ligase
Werner Syndrome (premature ageing)
caused by mutationin WRN coding for RECQ helicase causing helicase to not go into the nucleus.
Bloom Syndrome
loss of function mutation in RECQ helicase which normally stop wrong homologous recombination and fork stalling.
patients have sun sensitivity and butterfly patch on nose.
processivity
an enzyme’s ability to catalyze consecutive reactions without releasing its substrate.
factors that enhance DNA polyermase processivity
sliding clamp
single stranded DNA binding proteins (SSBs)
DNA topoisomerases
sliding clamp
clamp loader (replication factor C) + sliding clamp (PCNA) bind onto DNA polymerase δ. They displace primase and reel DNA through the polymerase
uses ATP
single stranded DNA binding proteins (SSBs)
keep replication fork open and stop the formation of DNA hairpins (DNA annealing to itself)
DNA topoisomerases
relax tension of unwound DNA
type 1 - nick and reseal 1 strand without ATP
type 2 - nick and reseal 2 strands with ATP
origin of replication
where replication begins (oriC in bacteria)
PreRC
pre-replicative complex
origin recognition complex (ORC), Cdc6, Cdt1, Helicase Mcm2-7
initiation of replication
1) replicator sequence in G1 -> PreRC licenses replicator sequence
2) origin activation in S -> Cdk activates PreRC to unwind DNA and recruit DNA polymerase
high Cdk activity inhibits formation of new pre-RC, and activates existing pre-RC
Cdk mutant
Mcm2-7 helicase loaded onto already replicated DNA carries out further ‘illegal’ replication
Telomerase
a ribonucleoprotein which uses reverse transcriptase and its RNA subunit containing AUCCCAUC to add TTAGGG repeats onto the 3’ end of DNA so the gap on the 5’ end can be filled in
