Does DNA replication follow the conservative,
semiconservative, or dispersive model?
The Correct Answer and Explanation is :
DNA replication follows the semiconservative model.
In semiconservative replication, each new DNA molecule consists of one original (parental) strand and one newly synthesized strand. This model was first proposed by Watson and Crick and later confirmed through the famous Meselson-Stahl experiment in 1958.
Explanation:
- What is DNA replication?
DNA replication is the process by which a cell duplicates its DNA before cell division, ensuring that each daughter cell receives an exact copy of the genetic material. - Three Proposed Models:
- Conservative: The entire parental DNA molecule remains intact, and a completely new molecule is synthesized.
- Semiconservative: Each parental strand serves as a template for a new complementary strand. The result is two DNA molecules, each with one parental and one new strand.
- Dispersive: Parental DNA is fragmented, and the new molecules are a mixture of old and new DNA segments throughout their length.
- Experimental Evidence:
The semiconservative model was confirmed by the Meselson-Stahl experiment. In this experiment, E. coli were grown in a medium containing heavy nitrogen isotope ((^{15})N) and then switched to a medium with light nitrogen ((^{14})N). DNA was extracted and analyzed using density-gradient centrifugation. The results showed intermediate and hybrid bands consistent with the semiconservative model. - Mechanism:
During replication, the enzyme helicase unwinds the double helix, separating the two strands. Each strand acts as a template, and DNA polymerase synthesizes a new complementary strand by adding nucleotides according to base-pairing rules (A pairs with T, and G pairs with C).
This semiconservative nature ensures both accuracy and stability, preserving the genetic code through generations. It also explains how mutations can occur if errors arise during replication, contributing to evolution and diversity.