DNA replication semi-conservative model
Introduction
The Meselson-Stahl experiment was an
experiment to prove that DNA replication was
semiconservative.
Semiconservative replication means that when the
double stranded DNA helix was replicated, each of
the two double stranded DNA helices consisted of
one strand
Nitrogen is a major constituent of DNA, the
genetic material of all cells.
It is commonly found in the 14N isotope, but it can
also be found in the heavier 15N isotope.
E. coli were grown for several generations in a
medium with 15N.
The DNA of the resulting cells had a higher density
(was heavier).
E. coli cells with only 15N in their DNA were put
back into a 14N medium and were allowed to
divide only once.
DNA was then extracted from a cell and was
compared to DNA from 14N DNA and 15N DNA.
It was found to have exactly an intermediate
density. This supported the idea of
semiconservative replication.
The DNA was intermediate in density because it
had an all 15N DNA strand and an all 14N DNA
strand. The all 15N strand was one of the original
strands in the original cell. The all 14N strand was
a newly synthesized strand.
DNA replication or DNA synthesis is the process of
copying a double-stranded DNA strand, prior to
cell division
The two resulting double strands are identical,
and each of them consists of one original and one
newly synthesized strand.
This is called semiconservative replication.
The process of replication consists of three steps,
initiation, replication and termination
Or following diagram