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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