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Module 2: DNA replication
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In-depth and detailed notes on module 2 of molecular biology which goes over DNA replication. It includes notes on the recommended readings as well.
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Lecture 1 possible types of DnareplicationNA replication the two Dna strands separate and Dna is copied using the Dna is copied using the
parent strand as a template
complementary base pairing provides an obvious way for a double stranded Dna molecule to
replicate
methods of DNAreplication
semiconservative replication
method of replication in whicheach nucleotide derived from the
daughter molecule contains one poly
original molecule and one newly synthesized strand
most straightforward scheme and the one favorited by watson and crick
conservative replication
onemoleculewithan original Dna and another molecule that has all new Dna
nucleotides while the other daughter contains both
one daughter molecule contains both parent poly
newly synthesized strands
conservative model seemslesslikely because it would require that the newly synthesized strandsdetach
from their templates and reassociate with one another Appears as a pointless extra step
sispersivereplication
Eachstrand of the daughtermolecules is composed partly of the original poly
nucleotide and partly
of the newly synthesized molecule
would require repeated template switching which would also be an unnecessary elaboration
In the naso's this is what most scientist thought happened as the methods of semiconservative were
thought to be impossible
Experiments were therefore carried out soon after the discovery of the double helix to determine
which of the three replication models is correct
Experiments demonstrated that Dna replicates semiconservatively
, the meselson stan experiment
carried out in nasa to distinguish between the three modes of Dna replication and work out
which occurs in Ecoli
procedure
A culture or bacteria weregrown in a medium containing heavy nitrogen
mostcommon isotope has an atomic weight or nu MN
Heavy isotope has an atomic weight or is ish
Nitrogen is a component of Dna bases so it cangetinto bacterial DNA
they added SNHaa heavyammonium chloride to the bacterial culture medium
All of the bacteria's Dna became labelled with Isn
Dna isplaced on top of cesiumchloride Gm
solution is centrifuged at soooo for 48hours
a density gradient is formed in the solution
normal Dna has a lower density contop of the tube
SN runs further down as it is heavier and is spun
down further than lighter DNA
culture of bacteria that contains all heavy DNA
Heavy Dna bacteria are transferred to culturemedium that
contains the light nitrogen isotope
theyare left to grow for various amounts of time and then
their Dna is isolated It take 20min for bacteria to undergo
one cell replication
intermidiate onelightbandand
hair Dna is heavy oneintermediate
Demonstrates semi
conservative replication
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