Eukaryotic DNA Replication

Eukaryotic and Prokaryotic replication similarities

Many DNA polymerases with specialized functions, semi-conservative, bidirectional, template and primer-dependent, 5' --> 3' synthesis, continuous leading strand, discontinuous lagging strand, some high-fidelity DNA polymerases

Eukaryotic chromosome size and shape

linear and much longer than prokaryotic chromosomes

DNA polymerase

has both DNA Pol δ and DNA Pol ε

Eukaryotic origin of replication

30,000 - 50,000 origins in human chromosomes

origins around 25,000 bps apart, locations vary across cell types

origins usually in AT-rich element and associated with actively transcribing genes (easier access)

Eukaryotic helicase

MCM

DNA pol ε

Leading strand synthesis

high processivity and proofreading

DNA pol δ

Lagging strand synthesis

"Strand-displacing" polymerase

proofreading

DNA Pol α-primase

Complex with primase for RNA primer synthesis and a separate DNA synthesis activity

Replication Protein A (RPA)

single strand DNA binding protein (SSB)

Flap endonuclease 1 (FEN1)

RNA Removal

DNA ligase

repairs nicks and joins Okazaki fragments

End-replication issue

Ends shorten with each replication

linear chromosomes- ends are substrates for repair enzymes and nucleases

primer requirement but no template available at ends

Telomeres

chromosome ends that protect it

TG (longer) and CA (shorter) strands with no genes

Telomere critical length

No more cell division- permanent G0 (senescence) or apoptosis

Telomerase

Reverse transcriptase, ribonucleoprotein (RNA + protein)

contains an internal RNA with CA-rich repeat that serves as a template

Telomere synthesis

Telomerase template RNA anneals to existing TG sequence at a telomere, catalyzes 5' --> 3' DNA synthesis of TG strand

Telomerase shifts so template RNA anneals to newly synthesized DNA.

repeat process