explain semi conservation of replication
Answers
ANSWER :-
REPLICATION :-
》The process by which the synthesis of new DNA molecule from pre existing DNA takes place is called replication.
》Replicates during the synthetic phase of the inter phase of the cell cycle.
Semiconservative Method of Replication:-
》Semiconservative Method of Replication was proposed by Watson and Crick.
》During semi conservative replication the two strands of a DNA molecule separate.
》This is by the breakage of hydrogen bonds between the complementary base pairs.
》Each separated strands act as a template for the synthesis of a new strand.
》The new strand is formed by bases complementary to its template strand.
》In each of the daughter DNA molecule one strand is old (from the parent) and the other strand is new. This mode of replication is called semi- conservative.
MEASELSON AND STAHL EXPERIMENT :-
(Evidence for semi conservative replication)
》 Measelson and Stahl (1958) demonstrated the semi-conservative mode of replication in E.coli.
》In this experiment E.coli was culture in a medium containing nitrogen salt labelled with heavy or stable isotope of N15 ( the common isotope of nitrogen is N14 (NH4Cl).
》The N15 was incorporated in both strands of DNA of E. coli and thus DNA becomes heavier,this DNA is called heavier DNA.
》Another preparation was also made in which E.coli was cultured in medium containing N14.
》N14 was also incorporated in both stands of DNA of E.coli.
》This DNA was lighter than the DNA of E.coli grown in N15 medium.
》The heavier and lighter DNA can be separated by Ceasium chloride density gradient ultracentrifugation.