Facts About DNA Replication
Facts about DNA Replication
Genetic information is carried out from parents to their offsprings by a proper replication of the parental DNA molecules. Usually the information is present in one or more double stranded DNA molecules. Replication of double stranded DNA is a more complex and multistep process because; a supply of energy is needed to unwind the twist. Moreover, single enzyme can catalyze only a small number of physical and chemical reactions, but in replication, many types of reactions are involved.
The most important fact about the DNA replication is that it has a self complementary nature i.e. each of the two strands of every parental DNA molecules acts as a template for the development of a complementary daughter strand.
In the cell, both strands of a DNA template are duplicated concurrently at an arrangement known as replication fork. Initially, the replication fork needs the separation of the two strands of DNA to produce the single stranded DNA (ssDNA) that is essential for the binding of DNA helicase and to act as a template for the formation of both the RNA primer and new DNA. The specific sites at which DNA unwinding and initiation of replication take place, are known as origin of replication. Depending upon the organisms, there may be one or as many as thousands of origins of replication per chromosome.
DNA replication starts with the “unzipping” of the parent molecule as the hydrogen bonds between the base pairs are broken down. Once unwind, the base sequences on each of the separated strands act as a template to guide the incorporation of a complementary base pairs on the strand being synthesized. As both strands of DNA go antiparallel with respect to each other, only one of the two template strands is replicated in a continuous manner. That strand is called leading strand. The other strand must be synthesized as a series of short DNA fragments, called okazaki fragments and that strand is called lagging strand. Both leading and lagging strands are initiated by the enzymes called DNA Polymerases. Another enzyme, DNA Ligase switches the okazaki fragments together to form one continuous DNA strand.
In addition to DNA polymerases, some proteins also play an important role in DNA replication reactions. These additional factors facilitate the unwinding of double stranded DNA template and stabilize the single stranded DNA template and remove the supercoils produced in front of the replication fork. These factors are called topoisomerases.
Finishing DNA replication needs the specific enzymes. For circular chromosomes, type II DNA topoisomerases are required to separate the topologically linked circular products from one another. Linear chromosomes also require some special enzymes to ensure their complete replication.