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Chapter 3

BIO130H1 Chapter Notes - Chapter 3: Okazaki Fragments, Dna Gyrase, Dna Replication

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Melody Neumann

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Week 3 Readings part 2 - DNA replication
Pg. 546-559
Pg. 769-770
DNA Replication
Semiconservative Replication
semiconservative: each daughter duple contains one strand from the parent
conservative : original strands remain together, as would the newly
synthesized strands
dispersive: parental strands broken into fragments.
The Meselson-Stahl experiment demonstrated that DNA replication in bacteria is
Replication in Bacterial Cells
Early approaches:
temperature sensitive(ts) mutants, the deficiency only reveals itself at an elevated
temperature, termed non permissive (or restrictive) temperature. When Grown at low
(permissive) temperature, the protein can carry out normal function
the development of in vitro system: replication can be studies using purified cellular
Replication Forks and Bidirectional Replication
replication begins at the origin
a number of proteins bind together to initiate the process
the process goes bidirectionally
replication forks: the pair of replication segment coming together
two move in opposite direction
Unwinding the duplex and separating the strands
enzymes such as DNA gyrase (a type II topoisomerase) relieve the mechanical
strain in E coli
The properties of DNA polymerase
DNA polymerase: the enzymes that synthesize new DNA strands.
the enzyme requires the presence of template DNA and all four
deoxyribonucleoside triphosphate
unseparated double strand cannot serve as template
single stranded DNA circle cannot serve as a template for DNA polymerase
because the enzyme cannot initiate the formation of a DNA strand
it needs a trends that provides the necessary 3’OH term -- primer
2 requirements of DNA polymerase:
a template DNA
a primer
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