Describe the Semiconservative method of DNA replication.

Explanation

The process of formation of a new copy of DNA from the existing one is called replication of DNA. It takes place by semi conservative method ic. one strand of parent molecule is conserved in the daughter molecule of DNA. This mechanism was proposed by Watson and crick and experimentally proved by Meselson and Stahl.
Requirements:DNA templates. Unwindase, RNA primer. RNA polymerase. DNA polymerase I and III. DNA ligase and deoxyribonucleotides
Steps:
(1) Unwinding of DNA: Due to the activity of REN nicking of DNA strand takes place at a specific point to form orisite Unwinding of DNA takes place from orisite, with the help of enzyme unwindase or helicase. The two separated strands of DNA look like Y-shape and is called replication fork. The separated DNA strands act as templates for the synthesis of new strand.
(2) Synthesis of RNA primer: RNA primer is a short segment of RNA (8-10 nucleotides) synthesized on DNA template with the help of RNA polymerase or primase. The synthesis of RNA primer is required as the enzyme DNA polymerase III can not directly initiate the synthesis of new DNA strand on the template.
(3) Formation of leading and lagging strands: Formation of new DNA strands by DNA polymerase enzyme can occur only in S' to 3' direction. Synthesis of new complementary strands takes place on both the templates in opposite directions. Now complementary Strand that is formed towards the replication fork on Template strand is continuous and is called leading strand or continuous strand. The synthesis of the other new complementary strand from the replication fork occurs discontinuously on parental strand and is called Tagging grand or discontinuous strand. This lagging strand will have small segments of RNA primer to which DNA nucleotides are joined. These are called Okazaki fragments.
(4) Formation and separation of daughter DNA molecule:In this step RNA primers are removed by the DNA polymerase and the gaps are filled up by the DNA nucleotides by the came envie. Then short segments of DNA are joined by DNA lipase forming a continuous strand of DNA. Thus each daughter DNA molecule will have one old parental strand and one new strand and hence it follows a semi conservative method of DNA replication.