Download DNA polymerase I

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
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 –
proofreading
More 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.
Sequence in the E. coli replication origin ori C
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
DNA ligase
Termination of chromosome replication in E.Coli
Ter - 20 base pair sequence
Ter sequence bind to protein Tus – Tus-Ter complex arrest replication fork
Separation of chromosomes
DNA Repair
1.
2.
3.
4.
Mismatch Repair
Base Excision Repair
Nucleotide Excision Repair
Direct Repair
1. Mismatch repair
2. Base Excision Repair
3. Nucleotide Excision repair
4. Direct repair
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.
Homologous Recombination and Holliday intermediates
Effects of site-specific recombination
Genetically Modification
Transposons