dna metabolism dna replication dna repair dna recombination
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DNA metabolism DNA replication DNA repair DNA recombination. Map of E.coli chromosome. Meselson-Stahl experiment – DNA replication is semi conservative. DNA replication. Nucleases (eg DNases) degrade DNA - PowerPoint PPT PresentationTRANSCRIPT
DNA replication
Nucleases (eg DNases) degrade DNA
Exonucleases – degrade nucleic acids from one side of the molecule 5’ → 3’ or 3’ → 5’.
Endonucleases – degrade at any site in a nucleic acid strand or molecule
DNA replication is very accurate – proofreadingMore than 90% of DNA polymerase activity in E.coli is carried out by DNA Polymerase I.
DNA polymerase I is not the primary enzyme of replication but has clean-up functions during replication, recombination and repair.
DNA polymerase II – DNA repair
DNA polymerase III – principal replication enzyme in E. coli.
DNA polymerases IV and V are involved in SOS response (repair of extensive DNA repair).
Nick translation
Nick (a broken phosphodiester bond, leaving a free 3’ and a free 5’ phosphate) occurs where DNA synthesis is to start.
Initiation of replication
DnaA – recognises origin sequences and open duplex at specific site
HU – Histone like protein, DNA bending proteins, stimulates initiation
DnaB – unwinds DNA
DnaC – required for DnaB binding at origin
Termination of chromosome replication in E.Coli
Ter - 20 base pair sequence
Ter sequence bind to protein Tus – Tus-Ter complex arrest replication fork
DNA recombination
Meiosis
Homologous genetic recombination – (also called general recombination) involves genetic exchange between any two DNA molecules that share an extended region of nearly identical sequence.
Site-specific recombination – differs from homologous recombination in that the exchanges occur only at a particular DNA sequence.
DNA transposition – is distinct from both classes in that it usually involves a short sequent of DNA with the remarkable capacity to move from one location in a chromosome to another.