Question

What is meant by semi conservative replication? How did Meselson and Stahl prove it experimentally?

Class XII
Molecular basis of inheritance

Answer 1

Semi-conservative mode of replication:

Replication is said to be semiconservative because of the following reasons :

• Two copies of a single DNA is produced during replication.

• The newly formed DNA copies contain 50% of the DNA strands contributed from the parent DNA molecule and the rest 50% replicated from the template strand.

• Hence direct contribution of the parent DNA molecule is only 50% , hence semiconservative.

Meselson and Stahl Experiment:

The following steps were performed :

• Heavy isotope of nitrogen (N-15) was incorporated into the DNA molecule of E. Coli and was allowed to replicate in a normal N-14 environment.

• After replication , it was found that the heavy isotope of nitrogen was found in 50% of the DNA strands while the rest were contributed by the N-14 nitrogen.

• Hence the contribution is only 50%.

HENCE , REPLICATION IS SEMI-CONSERVATIVE.

Answer 2

Answer:

Semiconservative replication describes the mechanism by which DNA is replicated in all known cells. It derives its name from the fact that this mechanism of transcription was one of three models originally proposed for DNA replication. The deciphering of the structure of DNA by Watson and Crick in 1953 suggested that each strand of the double helix would serve as a template for synthesis of a new strand. However, there was no way of knowing how the newly synthesized strands might combine with the template strands to form two double helical DNA molecules.

The semiconservative model seemed most reasonable since it would allow each daughter strand to remain associated with its template strand. The semiconservative model was anticipated by Nikolai Koltsov, supported by the Meselson-Stahl experiment and other even more revealing experiments that allowed for autoradiographic visualization of the distribution of old and new strands within replicated chromosomes.

The rate of semiconservative DNA replication in a living cell was first measured as the rate of phage T4 DNA strand elongation in phage-infected E. coli. During the period of exponential DNA increase at 37 °C, the rate of strand elongation was 749 nucleotides per second. The mutation rate per base pair per round of replication during phage T4 DNA synthesis is 2.4×10−8. Thus semiconservative DNA replication is both rapid and accurate.

Explanation:

please mark me brainliest