DNA Replication And Cell Division
Copyright © 2005, Dr.Richard Waller
DNA replication basically means creating two entire DNA strands for
each daughter cell in place of the single parent cell. Prior to the
cell division, its DNA within the nucleus is released by an enzyme
to break the hydrogen bonds between the bases, resulting in two
halves of the DNA. The uninhibited nucleotides within the nucleus
bonds with the bases of both strands. Bonds with T alone while C
with G, leading to exact matches for both strands.
There are four phases in cell division, or mitosis (normal cell
division, meiosis forms sex cells).
Prophase: Pairing of chromosomes occurs and following replication,
the parent cell has two complete sets. Two poles are formed as the
nucleus disappears.
Metaphase: Alignment of the chromosomes is at the equator between
the two poles.
Anaphase: The chromosomes split up towards each pole. Cell membrane
division begins.
Telophase: Appearance of nuclei is at each pole and membrane
divides. Two cells possess identical chromosomes.
DNA Replication
The DNA composition where two separate strands store all genetic
information, replicate easily. A DNA molecule has a polymer opposite
of the other, like a photonegative. One side enables the other to be
recreated. This duality simplifies copying a DNA molecule
remarkably.
Replication causes synthesization of DNA molecules. First a helicase
enzyme unwinds the double helix, at any point on the strand,
progressing to two replication forks by enzymes extending the helix
release in both directions. With unwinding and straightening out of
the DNA, DNA polymerase, another enzyme functions. It matches the
exposed nitrogenous bases with new nucleotides from the surrounding
nuclear fluid. The nucleotides and separated polymers fuse as per
the regular Watson-Crick pairing rules. The completion of the
separation and re-matching of the DNA molecule makes two perfect
copies.
DNA replication remains partially unknown. Signals that start the
process, the reason some cells don't replicate and the cause of
uncontrollable replication of cancerous cells remain unexplained.
Replication in Prokaryotes
Prokaryotes or bacteria store almost the entire genetic information
of an organism in a single large circular DNA ring and not in
multiple chromosomes of DNA strings with unconnected ends. This
replication is almost identical to eukaryotic DNA except in the use
of only two replication forks. Eukaryotes and prokaryotes differ,
with multiple replication sites active simultaneously in the former
and the speed of the latter requiring only two, one for each
direction The rate of replicating bacterial DNA is almost one
million base pairs per minute whereas the average is 500 to 5000
pairs for other organisms.
DNA Replication is Semi-Conservative
On completion of the replication process, two DNA molecules result,
which are identical both to each other as well as to the original.
There is not the slightest alteration in each strand of the original
molecule due to its role as the template for the synthesis of a
complementary strand. This replication method has been termed semi-
conservative; as one half of each new DNA molecule is old while the
other half is new.
Finally…
The need for DNA replication or cell genome duplication is created
by each cell division. As with all cellular activities, specialized
proteins are needed for the purpose of replication. DNA replication
is surprising as a process in all organisms except in the case of
humans where comprehension can prove very complex.
Learn more about Cell Biology and DNA replecation, visit
www.biology-online.org
© 2005 Dr.Richard Waller.
Dr.Richard Waller has been helping thousands of infetile couples and
gave hope to childless women since 1999 through the process of in-
vitro fertilization. He is based in England.
www.biology-online.org
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