Explain how DNA replicates, semi-conservatively during interphase.
Answer:
Helicase unwinds parental double
helix into 2 individual strands. The weak hydrogen bonds holding the base pairs
break. Single-stranded binding proteins help to stabilize them and prevent the
strands from reannealing to form double-stranded DNA. The primase synthesizes a
short RNA primer to give the DNA polymerase a place to start. The DNA
polymerase III elongates the strand by adding new deoxyribonucleotides one by
one. Complementary base pairing occurs. The complementary strand is called
leading strand and is formed continuously from 5’ to 3’,towards the replication
fork. The sliding clamp protein helps hold the DNA polymerase onto the DNA as
the DNA polymerase III moves along the DNA template strand. As the DNA elongation
proceeds, RNAase H removes the RNA
primer bound to the DNA template. A different DNA polymerase(DNA polymerase I)
then replaces the degraded RNA primer with DNA nucleotides. The lagging strand
is formed discontinuously. DNA polymerase III adds nucleotides to the primer to
form a short Okazaki fragment. DNA ligase joins the Okazaki fragments to form
the lagging strand. When the replication is complete, 2 DNA molecules are
formed. Each DNA molecule has 1 parental strand and one new complementary
strand.
Assignment submitted by S.M., Kang, E.S., Ong, T.W., Tan, K.Y., Ho. X.H., Wong 2011/2012 (IBM)
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