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
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What are common & different proteins of DNA synthesis in leading & lagging strands?
Coordinated DNA synthesis
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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
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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
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DNA replication act in a coordinated manner to synthesize both leading and lagging strands of DNA simultaneously at the replication fork
Origin of replication
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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
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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
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Priming of replication
Binding of Initiator proteins
Binding of Helicase
Binding of Primase
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Initiation of replication
Replication origin is a unique binding sites for DNA polymerase assembly to initiate DNA replication: DNA polymerase holoenzyme
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Why is DNA replication initiated at the origin?
Protein structure of Helicase: Single-stranded region is required
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Why is DNA replication initiated at the origin?
Assembly of Initiator proteins: Right time & Right place
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Replication of prokaryotic DNA
Single origin is sufficient to direct the replication of prokaryotic genome
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Replication of eukaryotic DNA
Multiple origins are needed to direct the replication of eukaryotic genome
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Experimental identification of origins of replication
Basic functional assay in molecular biology: Selective marker & Molecular cloning
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Termination of replication
Circular DNA DOES NOT have free ends of DNA: Complete replication in the termination zone
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Termination of replication
Linear DNA have free ends of DNA: Compromising in the replication & integrity of DNA
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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
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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