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DNA Replication
(^) (Ch 28.3-4)
Tues 4/21/
Stages (common to replication, transcription, translation) Initiation
(^) - at origin
TerminationElongation - processive, fast 2000 bp/s: copies E coli in < 40 min
Mechanism: template, primer, 5โ
3โ, enforcing WC bpโs
Bidirectional: replication fork ReplisomeOkazaki fragments joined by DNA ligaseRNA primersLeading strand continuous; lagging strand discontinuous ProofreadingProcessive - sliding clampDNA polymerase III
Replication in eukaryotes - some differences Ends = telomeres replicated by telomeraseDNA packaged in chromasomesInitiation at multiple sites (since bigger genome & slower)
Fork movement
Trends in Microbiology 15
, 156 (2007).
5โ 3โ synthesis
Replisome model
previous primer*)complete (encountersOkazaki fragmentDNA released whenNext:
Importance: DNA Damage & Repair
(^) only DNA is repaired
DNA damage EnvironmentSpontaneous: deamination, depurinationReplication errors (if not caught by proofreading) ChemicalsRadiation: UV - pyrimidine dimers Ames testNitrates - promote deaminationAlkylating agents - methylation of bases
Repair mechanisms Recombination - repair double-stranded breaksExcision repair - cleave, polymerize DNA, ligateDirect repair - alter base, no cleavageMethyls mark parent (correct) chain for replication errors
1/ (^) per day (^7)
1/10Purines:
(^) per day (^5)
Spontaneous:
deamination, depurination
