DNA replication: origins, fork machinery, leading/lagging strand, telomere maintenance.
Replication
DNA replication
Semiconservative duplication of the genome (Meselson-Stahl 1958), catalysed by DNA polymerases at replication forks initiated at origins.…
Replication fork
Moving Y-shaped junction at which parental duplex is unwound and both daughter strands synthesised. Houses helicase, primase, polymerases,…
Origin of replication
Locus where replication initiates. Bacteria have single oriC (245 bp AT-rich); eukaryotes use multiple origins licensed by ORC + Cdc6 +…
DNA polymerase
5′→3′ template-directed polymerase with nucleotidyl-transferase mechanism. Replicative polymerases (bacterial Pol III; eukaryotic α/δ/ε)…
Okazaki fragment
Discontinuous 1-2 kb (bacteria) / 100-200 nt (eukaryotes) DNA fragments synthesised on the lagging strand, each primed by a short RNA,…
Helicase
ATP-dependent motor that unwinds duplex DNA ahead of the replication fork. Bacteria: DnaB (5′→3′). Eukaryotes: CMG complex…
Telomere
Repetitive DNA-protein cap at eukaryotic chromosome ends (TTAGGG in vertebrates) that buffers end-replication loss. Shortens with each…
Telomerase
Ribonucleoprotein reverse transcriptase (TERT catalytic subunit + TERC RNA template) that extends 3′ telomere overhangs. Active in stem…
Replication timing programme
Genome replicates in a deterministic spatiotemporal order — euchromatin early, heterochromatin late. Associated with gene expression,…
Replication stress
Stalled/collapsed replication forks from nucleotide shortage, DNA damage, R-loops. ATR-Chk1 response. Key cancer hallmark; targetable by…