Lecture 6 Flashcards
(22 cards)
cell cycle stages
M > G_1 > S > G_2
G_1
gap phase. rapid growth and metabolic activity. longest phase.
cell cycle phase of DNA synthesis
S phase
G_2
short phase. growth and preparation for division
eukaryotic DNA polymerase alpha
Polymerase activity, Primase activity. leading/lagging strand synthesis. Repair.
eukaryotic DNA polymerase beta
polymerase activity. repair.
eukaryotic DNA polymerase gamma
polymerase activity, 3to5 exonuclease (proofreading), located in mitochondria, mitochondrial dna replication and repair.
eukaryotic DNA polymerase delta
polymerase. 3to5 exonuclease (proofreading), lagging strand synthesis. repair.
eukaryotic DNA polymerase epsilon
polymerase. 3to5 exonuclease (proofreading), 5to3 exonuclease, leading strand synthesis. repair.
functions of other dna polymerases
bypass repair and bypass synthesis
how is eukaryotic replication different
multiple origins of replication. chromatin is disrupted and reassembled. special mechanism for replicating tips.
acetylation of chromatin histone tails
deacetylated in closed chromatin = inactive replication.
eukaryotic replication initiation sequence of events
ORC on ORI, Cdc6 and Cdt1 bind ORC, Cdc45 and Sid3 bind ORC, Cdc6 loads Cdc45 onto DNA, Cdc6 eliminated, MCM (helicase) onto DNA which unwinds DNA, Ddc45 recruits polymerase alpha to initiate S phase, S-CDK and DDK are kinases that phosphorylate ORC proteins and trigger initiation
eukaryotic replication scheme
helicase unwinds, RFA proteins decorate strands, Pol alpha (primase) binds ends of open complex, pol alpha synthesizes rna primers (10 nts), pol alpha synthesizes DNA (~15 nts), pol epsilon replaces pol alpha, polymerase switching involving RFC, pol delta and PCNA
removal or rna primers
RNase H1 (endonuclease) removes most of primer, FEN1/RTHI (endo and exonuclease) removes remainder
solution to tip replication problem
telomerase.
telomerase mechanism
binds 3’ end of ss DNA region, 3’ end of DNA is extended using telomerase as template, telmoerase shifts to add an additional six nt repeat. …repeat
post telomerase replication
pol alpha binds to make rna primer followed by short DNA sequence, RFC displaces pol alpha and place PCNA onto DNA. Pol delta binds to RFC and PCNA and fills in missing DNA, ligase connects dna, nucleases remove primer.. still 3’ overhang!
eukaryotic replication initiation sequence of events
sufficient telomerase in cancer, germ, adult, and early embryonic cells. insufficient in non-germline (death of cell line after 20-60 generations)
Adult progeria (werner’s syndrome)
helicase associated. mutation in WRN gene (chrom. 8). autosomal recessive, premature aging. free from alzheimers and HBP.
WRN gene
3to5 dna helicase and 3to5 exonuclease, interacts with pol delta, interacts with Ku (involved in ds break repair)
Bloom’s syndrome
mutation in BLM gene (chrom. 15), 3to5 DNA helicase activity, part of BRCA1 supercomplex involved in DNA damage repair
