DNA Replication Lec. 3 Flashcards
(22 cards)
Initiation
replication bubble at ORI
ori- origin of replication and usually high amounts of A and T
ORC
Original recognition complex
attaches to ori and separates strands
Semiconservative
One old piece of ssDNA.
* One new piece of ssDNA
Helicase
breaks H-bonds to unzip dsDNA
Topoisomerase
Relaxes supercoiling of dsDNA because it often gets +supercoiled ahead of rep. fork
Primase
makes short RNA primer needed to initiate DNA synthesis
Ligase
joins ribose-phosphate backbones where two new strands meet
SSB
stabilizes ssDNA and prevents reannealing
DNA Poly
prokaryotes have dozens eukaryotes have about 12
replicates by extension but cannot start its own new strand
also proofreads
dsDNA antiparallel
polym travels 3 to 5 and synthesizes from 5 to 3
Okazaki fragments
Bound by ligase to form strand dna poly can’t bind
lagging strand
Terminus Problem
with every replication a 3 prime overhang forms where primer is degraded because poly cant fill in gaps in lagging strand
(more is removed every rep)
Telomeres
1000s of nucleotides capping chromosome ends.
* Non-coding: not part of any genes required to “do” something.
- can act as a primer for DNA synthesis
-caps prevent massive chrom. forming together
processivity
number of nucleotides that can be synthesized
FIdelity
how few mistakes are made during synthesis
Replisome
DNA polymerases on leading and lagging strands form pol dimer at fork.
* Joined by catalytic cores.
* Increase speed.
* Less likely to disassociate.
Accessory protein: β-clamp.
* Ring of proteins helps DNA pol slide along ssDNA
Redundant repair mechanisms
-Base-excision repair (BER).
- Post-replication mismatch repair (MMR).
- Nucleotide-excision repair (NER)
BER chemically altered bases.
* MMR for mismatches.
* NER for bulky lesions.
exonuclease
Mismatched bases “felt” by DNA pol.
* Lesion in backbone causes pol shape
change.
* Pushes exonuclease subunit of pol
into contact with nucleotide
leads to removal
Base excision Repair
-Most important after proofreading
DNS glyco-sylases cleave base-sugar bond
AP endonuclease makes cutout
dRpase removes stretch of DNA
polymerase snyth. new DNA
Ligase seals nicks
Mismatch Repair
Recognizes mismatched nucleotides
after replication.
* MutS protein “feels” and binds to
distortions in normal double helix.
* Triggers replacement of mismatched
nucleotide
Methylated DNA
Methyl group added to specific carbon in purine/pyrimidine ring.
Regulates transcription of genes,turning them on/off.
Heritable: passed on through semiconservative replication.
Nucleotide excision repair
damaged lesions recognized
special helicase separates on either side of lesion
strand removed and new DNA snythesized, ligase seals
