SCIE1106 Lecture Notes - Lecture 7: Dna Ligase, Dna Replication, Primase
L7 DNA replication
• Role of RNA primer
• Mechanism of leading and lagging strand
• Fx of proteins at DNA replication fork
• List major DNA polymerases of prokaryotes
and eukaryotes and their fx
• Care: DNA polymerase, DNA primase, RNA
primer, helicase , DNA ligase
https://www.youtube.com/watch?v=cDwJTLnGEyw
&t=642s
New DNA synthesis – 5’ → 3’ , alays euies
primer, initiates from origins
• dsDNA is pried/cleaved apart at replication
origin by helicase
• DNA polymerase fx- add 5’ nucleotides
GTAC to ’ ed of e strad,
• DNA polymerase fx- has proofreading
properties to error rate
Prokaryotes chromosomes – circular, short (E. Coli)
• Single replication origin
• Bidirectional synthesis ( → )
• Replication fork move away in opposite
direction from ori
red= new strands being formed as replication forks
process movement
• During DNA synthesis, replication bubbles
expand
Eukaryotes chromosomes – linear, long
• Multiple replication origin
• Its much longer, needs to speed up
replication
At replication fork
• There’ll e strads, is laggig is leadig
• Lagging strand- synthesized discontinuously –
are made as Ogazaki Fragments
• Several orgazaki fragments join together by
DNA ligase to form a continuous strand
DNA polymerase
• Catalyze DNA synthesis
• Add nucleotides (GTAC) to parent strands
• Cannot start a completely new strand, needs
a template
• Primer – poides 3’ OH- end, primer is a
short ds RNA
• DNA needs existing double strand (existing
prier that has ’ OH- end of RNA primer
before adding each nucleotide
• DNA primase – synthesize RNA primer
• DNA polymerase needs RNA primer (DNA
primase makes RNA primer)
In lagging strands of DNA synthesis
• Ogazaki fragments is primed by an RNA
primer (which is synthesized in a template,
dependent manner by DNA primase)
• DNA ligase – joins ogazaki fragments by their
sugar-phosphate backbone – making
phosphodiester bonds
• Primers, will eventually be erased, and
replaced by DNA, and then joined the
fragments together by ligase – caused by the
enzyme
pol1
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