Meselson-Stahl experiment

Definition

The Meselson-Stahl experiment was a groundbreaking scientific study conducted in 1958 that demonstrated the semiconservative nature of DNA replication. By using isotopes of nitrogen to label DNA strands, the experiment provided evidence that during replication, each new DNA molecule consists of one original strand and one newly synthesized strand. This finding is crucial for understanding how genetic information is faithfully passed on during cell division.

5 Must Know Facts For Your Next Test

1. The experiment utilized nitrogen isotopes, specifically N-14 and N-15, to differentiate between old and newly synthesized DNA strands.
2. E. coli bacteria were grown in a medium containing N-15, allowing their DNA to incorporate this heavier isotope before being transferred to a lighter N-14 medium.
3. After several generations, the DNA was analyzed using density gradient centrifugation, which separated the DNA based on density.
4. The results showed that after one round of replication, all DNA had an intermediate density, indicating that it contained one old and one new strand.
5. After two rounds of replication, there were distinct bands of light and intermediate density, further supporting the semiconservative model.

Review Questions

• How did the Meselson-Stahl experiment change our understanding of DNA replication?
  • The Meselson-Stahl experiment fundamentally changed our understanding of DNA replication by providing clear evidence for the semiconservative model. Prior to this experiment, there were competing hypotheses about how DNA replicated. By using isotopes and observing the density of DNA strands after replication, it became evident that each new double helix consisted of one original strand and one newly synthesized strand. This insight was crucial for advancing molecular biology and genetics.
• Evaluate the significance of using nitrogen isotopes in the Meselson-Stahl experiment.
  • Using nitrogen isotopes in the Meselson-Stahl experiment was significant because it allowed researchers to trace and differentiate between old and newly synthesized DNA strands based on density. The heavy isotope N-15 was incorporated into the bacterial DNA when grown in that medium, and upon switching to N-14, the lighter isotope was used for new synthesis. This innovative approach provided a clear visual representation of the semiconservative nature of replication and set a standard for future molecular biology experiments.
• Synthesize information from the Meselson-Stahl experiment with modern understandings of DNA replication mechanisms and their implications for genetic inheritance.
  • The findings from the Meselson-Stahl experiment not only confirmed the semiconservative model of DNA replication but also laid the groundwork for modern understandings of molecular mechanisms involved in genetic inheritance. Today, we know that enzymes like DNA polymerase play critical roles in adding nucleotides to growing strands while ensuring fidelity during replication. This semiconservative process is essential for maintaining genetic stability across generations, preventing mutations, and ultimately influencing evolutionary processes. The insights gained from this landmark experiment continue to inform research in genetics, biotechnology, and medicine.

Related terms

Semiconservative replication: A type of DNA replication in which each strand of the original double helix serves as a template for a new strand, resulting in two daughter DNA molecules, each containing one old and one new strand.

Isotope: Variants of a particular chemical element that have the same number of protons but different numbers of neutrons, resulting in different atomic masses.

DNA replication: The biological process by which a cell duplicates its DNA before cell division, ensuring that each daughter cell receives an exact copy of the genetic material.