Question

What was early experimental evidence for semi-conservative DNA replication carried out in?

Answer 1

The early experimental evidence for semi-conservative DNA replication was carried out in the Meselson-Stahl experiment.

Explanation

In the Meselson-Stahl experiment, they used isotopes of nitrogen (^14N and ^15N) to trace the replication process. Initially, the bacteria were grown in a medium with heavy nitrogen (^15N), making their DNA heavier. When they shifted to a medium with lighter nitrogen (^14N) and allowed replication to occur, they found that after one generation, the DNA showed an intermediate density—proving that each new DNA molecule contained one original strand (^15N) and one newly synthesized (^14N) strand.

This supported the semi-conservative replication model proposed by Watson and Crick. The experiment provided tangible evidence against the conservative and dispersive models of DNA replication. The consistent observation of intermediate DNA density in successive generations of bacterial DNA confirmed the semi-conservative nature of DNA replication.

This groundbreaking experiment demonstrated that DNA replication involves the separation of DNA strands and the synthesis of new complementary strands, confirming the semi-conservative nature of DNA replication, a pivotal concept in molecular biology.

Answer 2

The early experimental evidence for semi-conservative DNA replication was obtained in the bacterium Escherichia coli.

Step-by-step explanation:

In the early 1950s, scientists were exploring the mechanism of DNA replication, specifically whether it followed a conservative, semi-conservative, or dispersive model. The groundbreaking experiment demonstrating semi-conservative replication was conducted by Matthew Meselson and Franklin Stahl in 1958, using Escherichia coli as their model organism. They labeled the parental DNA with a heavy isotope of nitrogen (15N), and then allowed the bacteria to replicate in a medium containing a lighter isotope of nitrogen (14N).

In the first round of replication, the newly synthesized DNA strands had an intermediate density, as they were composed of one heavy (15N) and one light (14N) strand. This was confirmed through density gradient centrifugation. If DNA replication had been conservative, the second round would have produced a distinct heavy band and a distinct light band. However, the observed result showed a single hybrid band with intermediate density, supporting the semi-conservative model.

The experiment provided strong evidence for the semi-conservative nature of DNA replication, a fundamental concept in molecular biology. Meselson and Stahl's elegant design and careful analysis laid the groundwork for our understanding of DNA replication, demonstrating that each newly synthesized DNA molecule consists of one old strand and one newly synthesized strand.