topoisomerase during dna replication - kocwcontents.kocw.net/kocw/document/2015/korea_sejong/... ·...
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Topoisomerase during DNA replication
As the strands of parental DNA unwind, the DNA ahead of the replication fork is forced to be condensed 1] Topoisomerase I: Reversible breakage and rejoining of one strand in DNA 2] Topoisomerase II: Reversible breakage and rejoining of both strands in DNA
What are common & different proteins of DNA synthesis in leading & lagging strands?
Coordinated DNA synthesis
DNA replication act in a coordinated manner to synthesize both leading and lagging strands of DNA simultaneously at the replication fork
Coordinated DNA synthesis
http://www.hhmi.org/biointeractive/dna-replication-advanced-detail
The replication of DNA starts at sites called origin of replication which provides single-stranded DNA template for initiation of DNA synthesis
Origin of replication
Replication bubble
DNA replication act in a coordinated manner to synthesize both leading and lagging strands of DNA simultaneously at the replication fork
Origin of replication
Replication origin is a unique binding sites for proteins required to initiate DNA replication: Initiator proteins
Origin of replication
Single-stranded DNA template
DnaA : Initiator proteins DnaB: Helicase
Replication origin is a unique binding sites for primosome required to initiate DNA replication: Helicase & Primase
Priming of replication
DnaA : Initiator proteins DnaB: Helicase DnaG: Primase
Priming of replication
Binding of Initiator proteins
Binding of Helicase
Binding of Primase
Initiation of replication
Replication origin is a unique binding sites for DNA polymerase assembly to initiate DNA replication: DNA polymerase holoenzyme
Why is DNA replication initiated at the origin?
Protein structure of Helicase: Single-stranded region is required
Why is DNA replication initiated at the origin?
Assembly of Initiator proteins: Right time & Right place
Replication of prokaryotic DNA
Single origin is sufficient to direct the replication of prokaryotic genome
Replication of eukaryotic DNA
Multiple origins are needed to direct the replication of eukaryotic genome
Experimental identification of origins of replication
Basic functional assay in molecular biology: Selective marker & Molecular cloning
Termination of replication
Circular DNA DOES NOT have free ends of DNA: Complete replication in the termination zone
Termination of replication
Linear DNA have free ends of DNA: Compromising in the replication & integrity of DNA
Telomere & Telomerase: Maintaining the end of DNA
Free ends of linear DNA is extended as tandem repeat by telomerase
https://www.youtube.com/watch?v=AJNoTmWsE0s
Telomere & Telomerase: Maintaining the end of DNA
Free ends of linear DNA is protected by shelterin complex: Enzymatic and structural functions
Enzymatic function
Structural function