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9 Cards in this Set
- Front
- Back
DNA replication basics
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-DNA replicated in Sphase, with every cell division
-must be fast and efficient -semi-conservative-each new copy has one parent strand(template) and one daughter strand(primer) |
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DNA synth initiation
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REPLICATION ORIGIN-initial point of duplex separation
REPLICATION FORK-point of transition b/w duplex and ssDNA, Fork advances HELICASE PROTEIN-seperates duplex, requires E from ATP, induces pos. supercoiling ahead SINGLE STRANDED DNA BINDING PROT.(SSB)-coats ssDNA to stabilize it PRIMASE PROTEIN- uses (ribose)NTP's to late down short RNA primer DNA POLYMERASE-begins adding dNTP's to 3' end of primer |
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DNA synth elongation
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-DNA polymerase(Mg2+) adds dNTP's to 3' end
-some DNA pols have "editing" exonuclease activity(opposite thumb)-removes in reverse direction(removes nuc from 3' end) -Right Hand-DNA lies on palm, dNTPs captured by fingers and added to primer in "synthetic site"-b/w palm and fingers, palm and thumb domain constrain duplex-avoid wrong pairing -synthesis is Semi-Discontinuous -done in replisome |
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Semi-discontinuous Synth
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-Leading strand is continuously synth in 5' to 3' dirrection
-Lagging strand-discontinuous, primer is laid down and synth goes till hits 5' end of old primer-okazaki fragments -Several RNAses cleave RNA primer -Gap filled by DNA pol, leaving nick -nick sealed by DNA ligase 1 |
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processivity
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-processivity=#bp synthesized/binding event, ability of pol to remain bound
-processivity is increased by Clamp Proteins-donut w/ DNA in the middle -Eukaryotes-pol clamp=PCNA (proliferating cell nuclear antigen) |
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Replisome
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-replisome=1)helicase,2) two pol molecules(each w/ assoc. processivity clamps),3) and a primase molec
-Helicase puls pol behind it, lagging strand releases and reassociates(controlled by clapm prot) -ssDNA stablized by ssb when looped out b/w helicase and lagging pol |
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diff DNA pols
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POL ALPHA/PRIMASE:
-primes synth on lagging strand by laying down RNA primer then short DNA -not processive -no proofreading exonuc. act.-error prone(ok, b/c RNA is removed) POL DELTA: -processive (assoc. w/ PCNA) -does bulk of synth for both strands -has editing exonuc. act. POL EPSILON: -processive (but w/o PCNA) -substiture for POL DELTA -has editing exonuc. act. 8 MORE POLS: -primarily for DNA repair -less processive (no PCNA) -no editing(quick fix) |
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prokaryot replicon
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-replicon=unit of replication (1 initiation, 1 termination
-one replicon -seq=origin of replication -DNA is unwound and two replisomes work in both directions-bidirectional replication. -procedes till the replisomes meet at the terminus |
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eukaryot replicons and licensing
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-have many replicons/chrom to speed up replication
-all must be copied once in S phase -licensing factors controlled by cycle regulatory mechanisms -Replication licensing steps: 1)ORC (origin recognition complex) bind to replication origin in inactive form 2)Licensing factors (cdc6,MCM) bind adj. to ORC's and activate their ability to unwind the origin and assemble replisomes (*pre-replication complex*) 3)unwinding and fork advancement results in destruction of licensing factors 4)ORC's re-assemble at origins of daughter strands (inactive) called-*post-replication complex* |