Question

The experimental proof for semiconservative replication of DNA was first shown in a

• A. Fungus
• B. Plant
• C. Bacterium
• D. Virus

Answer 1

The Correct Option is C

The experimental proof for semiconservative replication of DNA was first demonstrated by Matthew Meselson and Franklin Stahl in 1958 using bacteria. The bacterium Escherichia coli (E. coli) was used in their experiment to conclusively show how DNA replicates in a semiconservative manner. Let's break down the reasoning and why "Bacterium" is the correct answer:

• Understanding Semiconservative Replication:
  • In semiconservative replication, each of the two strands of the original DNA molecule serves as a template for the formation of a complementary new strand. Thus, each new DNA molecule consists of one old (parental) strand and one newly synthesized strand.
• The Experiment:
  • Meselson-Stahl Experiment: They grew E. coli in a medium containing a heavy isotope of nitrogen, ^{15}N, until the DNA of the bacteria was fully labeled with the heavy nitrogen.
  • Then, they transferred the bacteria to a medium containing the normal isotope of nitrogen, ^{14}N, and allowed the bacteria to replicate.
  • After each round of replication, the DNA was extracted and analyzed using equilibrium density gradient centrifugation.
  • After one round of replication, the DNA formed a single band intermediate between the expected native DNA density and the density of fully ^{15}N-labeled DNA, supporting the semiconservative model.
• Excluding Other Options:
  • Fungus, Plant, Virus: None of these were used in the original experiments that demonstrated semiconservative replication. Although DNA replication occurs in fungi, plants, and viruses, the initial experimental proof came from work with bacteria.

Thus, the correct answer is Bacterium.