DNA is the molecule responsible for transmitting hereditary traits. In healthy cells, DNA
is transferred equally to daughter cells without being altered by cell division. Therefore,
before cell division, DNA Its amount is doubled. The creation of a copy of DNA by replication
is called replication. Replication, cell It takes place in the interphase phase of its division.
opposes each a new complementary chain is synthesized. Matthew Melson and Franklin
Stahl.They conducted an experiment to test the hypothesis about the semi-conservative
replication of DNA.
How Does DNA Replication Occur? DNA replication is an event in which many enzymes
play a role. In the environment for DNA to replicate itself adenine, guanine, cytosine and
thymine deoxyribonucleotides; DNA polymerase, DNA ligase, helicase enzyme; RNA primers
and magnesium (Mg) ions are required to activate DNA polymerase. Here Apart from the
enzymes mentioned, other enzymes are also involved in the replication of DNA. However,
here is the three enzymes will be mentioned in his mission. The replication of a DNA
molecule begins at specific sites called replication origins. Origin of replication They are
regions of DNA with special nucleotide sequences. Enzymes that initiate replication
recognize these sites.
There is an origin of replication in the cyclic DNA found in prokaryotic cells. Enzymes
that recognize this region are two separates the chain from each other. A replication fork is
formed on both sides of the bubble formed in this region. From these points replication
continues until all DNA has been copied in both directions.
In eukaryotic cells, DNA can contain hundreds or even thousands of replication origins.
DNA replication in eukaryotes, as in bacteria, proceeds in both directions from each origin of
replication. Each replication bubble has a replication fork at both ends. Therefore, many replication bubbles are formed. Inside each bubble DNA strands are synthesized semi conservatively.
DNA replication is an event that takes place with the activity of enzymes. The helicase
enzyme separates the ancestral chains from each other at the replication fork. Helicase,
hydrogen between nitrogenous bases It allows opening by breaking the bonds. Each strand
of DNA acts as a template for new DNA strands to be created. DNA polymerase is the
enzyme involved in the synthesis of new DNA strands. However, the synthesis of
polynucleotide can't start. It is a short RNA primer that initiates synthesis. DNA polymerase
III, more It enables the synthesis of the new chain by adding nucleotides to the 3′ end of the
pre-existing primary chains. DNA polymerase III is also involved in repairing errors in the
DNA strand. DNA ligase closes the gaps between new polynucleotide particles formed during
DNA replication. These DNA particles fuse together with the phosphodiester bond. Thus, a
complete chain is formed.
Special enzymes recognize the origin of replication. DNA replication proceeds in two
directions at the origin of replication. Thus, a replication bubble is formed. At each end of
the replication bubble is the replication fork. This At these points, ancestral DNA strands are
unraveled. DNA helicase enzyme works in the dissolution process. Some proteins that bind
to the strands of ancestral DNA prevent the strands of ancestral DNA from joining. This is
DNA strands serve as patterns for new strands of DNA. A short RNA primer inspects the
synthesis of the new DNA strand Initializes.
The direction of replication will move away from the replication fork because the other
new chain will be synthesized in the opposite direction It happens in the way. The chain to
be synthesized in this direction is synthesized intermittently. These fragments of the
intermittently synthesized chain are called Okazaki fragments, after the Japanese scientist
Reiji Okazaki (Reyci Okazaki). In the intermittent chain there is a separate RNA primer for
each Okazaki fragment. Each new RNA is attached to the 3′ end of the primer with a DNA
polymerase III adds nucleotides. RNA primers are removed by the enzyme DNA polymerase I.
DNA polymerase I, replacing missing nucleotides while DNA ligase binds the fragments in the
newly synthesized DNA strand together. Thus, both the chain is also completely synthesized.
Aziz Sancar, who received many awards during his nearly forty years of working life,
was finally awarded the 2015 Nobel Prize in Chemistry for his discoveries in the field of
mechanistic studies of DNA repair. He received his award at a ceremony held on December
10, the anniversary of Alfred Nobel's death. It was taken from the hands of Carl Gustaf.
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