Question

DNA replication is semiconservative as
(a) Only non-parent strand act as a template
(b) Both strands of the new molecule are synthesized de novo
(c) One of the strands in each new molecules is parental and the other is new
(d) Daughter strands are dispersive

Answer 1

Hint: Replication means the method of duplication. In molecular biology, DNA replication is the first phase of inheritance. Central dogma tells how the DNA builds its own copies by DNA replication, which then codes for the RNA in transcription and forward RNA codes for the proteins by translation.

Complete answer:
Meselson and Stahl proved that DNA shows the semi-conservative model. After replication, every DNA molecule contains one parental and newly synthesized strand. After replication of 1 DNA strand, each daughter helices includes one among the first parental helical strands and one copied helical strands.

Additional information: Meselson and Stahl Experiment was investigative evidence for semiconservative DNA replication. In 1958, Matthew Meselson and Franklin Stahl conducted an experiment on E.coli which divided in 20 minutes, to review the replication of DNA. $^{15}N$ (heavy) and $^{14}N$ (normal) are two isotopes of nitrogen, which may be distinguished from their densities by centrifugation in Caesium chloride (CsCl). Meselson and Stahl cultured E.coli during a medium containing $^{15}NH_4Cl$ over several generations. As an end, $^{15}N$ was fused into the bacterial DNA. Afterward, they changed the $^{15}NH_4Cl$ medium to normal $^{14}NH_4Cl$. At a daily interval of your time, they took the sample and checked for the density of DNA. Observation- Sample number 1 (after 20 minutes): The sample includes bacterial DNA with an intermediate density.
Sample number 2 (after 40 minutes): The sample includes DNA with both intermediate and lightweight densities within the same proportion.
So, the correct answer is ‘(c) One of the strands in each new molecule is parental and the other is new’.

Note: Messelson and Stahl’s experiment supported the semi-conservative mode of replication. Supported observations and experimental results, Meselson and Stahl concluded that DNA molecules can replicate semi-conservatively. The study of the semi-conservative nature of replication of DNA didn’t conclude there. Following the Meselson and Stahl experiment, Taylor and colleagues conducted another experiment on broad beans (fava beans) which again proved that replication of DNA is semi-conservative.