5.2 DNA replication Flashcards
why is it important foe our cells to reproduce
1-fix damaged organs/tissue
2-growth
3- body functions
DNA replication
the
process of producing
two identical DNA
molecules from an
original, parent DNA
molecule
semi-conservative
replication
the
mechanism of DNA
replication in which
each newly synthesized
DNA molecule is
composed of one
strand from the original
DNA molecule and one
new strand
In the process of semi-conservative replication, is process of replication is most o$en described in three basic phases what are they?
- In the initiation phase, a portion of the DNA double helix is unwound to expose the
bases for new base pairing. - In the elongation phase, two new strands of DNA are assembled using the parent DNA
as a template. “e new DNA molecules—each composed of one strand of parent DNA
and one strand of daughter DNA—re-form into double helices. - In the termination phase, the replication process is completed and the two new DNA
molecules separate from each another. At that point, the replication machine is dismantled.
origin of replication
the DNA sequence
where replication
begins
helicase
a group of
enzymes that aid in the
unwinding of DNA
a replication bubble,
initiation creates an
unwound, oval-shaped area called a replication bubble, with two Y-shaped regions at each
end of the unwound area.
a replication fork.
Each Y-shaped area is called a replication fork. As replication
proceeds, each replication fork moves along the DNA in opposite directions.
DNA polymerase III
an enzyme that adds
nucleotides to the
3! end of a growing
polynucleotide strand
Okazaki fragments
short DNA fragments
that are generated
during the synthesis of
the lagging strand in
DNA replication
primer
in DNA
replication, a short
segment of RNA that
is complementary to
a part of the 3! to 5!
DNA template strand
and serves as a starting
point for addition of
nucleotides
DNA polymerase I
an enzyme that
removes RNA primer
and fills gaps between
Okazaki fragments
on the lagging strand
with DNA nucleotides;
proofreads newly
synthesized DNA
DNA ligase
an
enzyme that catalyses
the joining of Okazaki
fragments
Correcting Errors during DNA Replication
these errors can be corrected by
one of several mechanisms, as you will see below.
1-One mechanism for correcting errors that occur during DNA replication involves
DNA polymerases.DNA polymerase I, along with DNA polymerase II, has an important
proofreading function. A$er each nucleotide is added to a new DNA strand, these
DNA polymerases can recognize whether or not the correct nucleotide has been added.
Replication is stalled when an incorrect nucleotide is added because the 3! hydroxyl end of
the incorrect nucleotide is in the wrong position for the next nucleotide to bond to it. When
this occurs, these DNA polymerases excise the incorrect base from the new strand and add
the correct base, using the parent strand as a template. “is proofreading step repairs about
99% of the mismatch errors that occur during DNA replication.
how is replication the different in eukaryotes and prokaryotes
- “e rate of replication is faster in prokaryotes (about 1000 nucleotides added per second)
than in eukaryotes (about 40 nucleotides added per second). Presumably, this is due to
more elaborate enzyme complexes that are required in eukaryotic replication and a more
stringent proofreading mechanism. - “e DNA polymerase enzymes in eukaryotes di#er from those in prokaryotes. “ey also
di#er in the number involved. To date, !ve have been identi!ed in prokaryotes, while 13
have been identi!ed in eukaryotes. - “e smaller circular chromosome of a prokaryote contains a single origin of replication.
“e larger linear chromosome of a eukaryote may contain thousands of origins of
replication.
how is replication the same in eukaryotes and prokaryotes
- require origins of replication
- have elongation occur in the 5! to 3! direction
- have continuous synthesis of a leading strand and discontinuous synthesis of a lagging
strand - require use of a primer for synthesis of Okazaki fragments in the synthesis of the lagging
strand - use DNA polymerase enzymes
mismatch repair
a
mechanism for
repairing errors
made during DNA
replication, whereby
a group of proteins
recognize a mispaired
nucleotide on the
newly synthesized
strand and replace it
with a correctly paired
nucleotide
telomere
a repetitive
section of DNA,
near each end of a
chromosome; the
presence of this
sequence helps to
protect from loss of
important genetic
information during
replication of the linear
DNA in eukaryotic cells
