Meselson-Stahl experiment

Definition

The Meselson-Stahl experiment was a groundbreaking study conducted in 1958 that demonstrated the semi-conservative nature of DNA replication. It showed that during DNA replication, each strand of the original double helix serves as a template for the formation of a new complementary strand, leading to two DNA molecules, each composed of one old strand and one newly synthesized strand. This experiment provided key evidence supporting the mechanism of DNA replication and deepened the understanding of genetic inheritance.

5 Must Know Facts For Your Next Test

1. The Meselson-Stahl experiment used nitrogen isotopes, specifically nitrogen-15 (heavy) and nitrogen-14 (light), to label bacterial DNA.
2. After several rounds of replication, the DNA was separated using density gradient centrifugation, resulting in distinct bands for different densities.
3. The results showed that after one generation, the DNA had an intermediate density, indicating that each molecule contained one heavy and one light strand.
4. Subsequent generations displayed bands corresponding to light DNA and intermediate DNA, confirming that the original strands were preserved in each new molecule.
5. This experiment provided crucial evidence against the conservative model of DNA replication, where both strands would remain intact in the original molecule.

Review Questions

• How did the use of nitrogen isotopes in the Meselson-Stahl experiment help illustrate the semi-conservative nature of DNA replication?
  • The use of nitrogen isotopes allowed researchers to distinguish between old and newly synthesized DNA strands. By incorporating nitrogen-15 into the bacteria's DNA and then switching to nitrogen-14, the researchers tracked changes in density after replication. The appearance of hybrid strands after one generation and lighter strands in subsequent generations provided clear evidence that each new DNA molecule consisted of one original strand and one new strand, thus supporting the semi-conservative model.
• What were the key results of the Meselson-Stahl experiment, and how did they contribute to our understanding of DNA replication mechanisms?
  • The key results showed that after one round of replication, all DNA had an intermediate density due to the presence of both heavy and light strands. In subsequent rounds, lighter strands began to appear. These findings directly supported the semi-conservative model by demonstrating that each new double helix was made up of one old strand and one new strand. This fundamentally changed our understanding of how genetic information is passed on during cell division.
• Evaluate the implications of the Meselson-Stahl experiment for molecular biology research and its impact on future studies related to genetics.
  • The Meselson-Stahl experiment laid the groundwork for molecular biology by confirming the semi-conservative nature of DNA replication, which has profound implications for genetics and heredity. It shifted scientific understanding away from earlier models and emphasized the importance of accurate replication for genetic stability. This clarity has paved the way for advancements in genetic engineering, biotechnology, and our overall comprehension of how mutations occur during replication, influencing countless research avenues in genetics and molecular biology.

Related terms

DNA Replication: The process by which a cell makes an identical copy of its DNA before cell division, ensuring that each daughter cell receives a complete set of genetic information.

Semi-Conservative Replication: A method of DNA replication in which each new double helix contains one original strand and one newly synthesized strand.

Isotope Labeling: A technique used in the Meselson-Stahl experiment to track the incorporation of nitrogen isotopes into newly synthesized DNA, allowing differentiation between old and new strands.