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Wednesday, 28 July 2021

The Process of Replication of DNA l Genetics l NEET l NTA l NOTES


The Process of Replication of DNA


¾    In Eukaryotes DNA replication takes place in S phase of cell.

¾   The process involves a number of enzymes/catalysts, of which the main enzyme is DNA-dependent DNA-polymerase, that catalyses of the polymerization of the deoxynucleotides at a rate of approximately 2000 bp per second.

¾    The process is also an energy-expensive process; deoxyribonucleoside triphosphates serve the dual purpose of 

--------- (I) acting as substrate and

---------- (II) providing energy (from the two terminal phosphates).

¾    The intertwined strands of DNA separate from a particular point called origin of replication.

¾    Since the two strands cannot be separated in its entire length, replication occurs with small opening of the DNA- helix; the Y-shaped structure formed, is called replication fork.

¾    The DNA-dependent DNA-polymerases catalyse polymerisation of the nucleotides only in 5’-3’ direction.

¾    Consequently, one of the template strands (with 3’-5’polarity) the synthesis of DNA is continuous, while on the other template strand (with polarity 5’-3’), the synthesis of DNA is discontinuous, i.e., short stretches of DNA are synthesised.

¾    The discontinuously synthesisted strands are later joined together by the enzyme DNA-ligase.

¾    A few additional enzymes (and their functions), other than DNA polymerase and ligase, that are involved in the replication of  DNA are:

i--helicases -- opens the helix

ii--topoisomerases -- removes the supercoiling of DNA

iii--Primase --synthesises RNA primer

iv--Telomerase--to synthesizes the  DNA of telomeric end of chromosomes.


Replicating Fork



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