key term - Meselson-Stahl Experiment

Definition

The Meselson-Stahl experiment was a groundbreaking study conducted in 1958 that demonstrated the semi-conservative nature of DNA replication. The experiment showed that when DNA replicates, each of the two new DNA molecules consists of one original strand and one newly synthesized strand. This experiment was pivotal in understanding the mechanisms of DNA replication and the role of enzymes involved in the process.

5 Must Know Facts For Your Next Test

1. The experiment utilized isotopes of nitrogen (N15 and N14) to label the DNA of E. coli bacteria, allowing researchers to track the incorporation of these isotopes during replication.
2. After several rounds of replication, the density gradient centrifugation technique was used to separate DNA based on its density, revealing distinct bands corresponding to different stages of replication.
3. The results confirmed that after one round of replication, all DNA had an intermediate density, indicating that each molecule contained one old and one new strand.
4. After two rounds of replication, two distinct bands were observed: one corresponding to hybrid DNA (one old and one new strand) and another for completely new DNA (two new strands).
5. The Meselson-Stahl experiment provided critical evidence supporting the semi-conservative model of DNA replication, which was essential for understanding how genetic information is passed on during cell division.

Review Questions

• How did the use of N15 and N14 isotopes contribute to the findings of the Meselson-Stahl experiment?
  • The use of N15 and N14 isotopes allowed researchers to label the original DNA strands distinctly from newly synthesized ones, enabling them to track changes during replication. By growing E. coli in a medium containing N15, all the DNA initially incorporated this heavier isotope. When switched to a medium with N14, the subsequent generations produced DNA with varying densities that could be separated through centrifugation, leading to clear evidence for semi-conservative replication.
• What were the key observations from the density gradient centrifugation technique in the Meselson-Stahl experiment that supported the semi-conservative model of DNA replication?
  • The key observations included the presence of an intermediate density band after one round of replication, indicating that each resulting DNA molecule consisted of one original strand and one newly synthesized strand. After a second round, two distinct bands emerged: one representing hybrid molecules (with one old and one new strand) and another representing fully new molecules (composed entirely of N14). These results were crucial in demonstrating that DNA replication follows a semi-conservative mechanism.
• Evaluate the implications of the Meselson-Stahl experiment on our understanding of DNA replication mechanisms and its impact on molecular biology as a whole.
  • The implications of the Meselson-Stahl experiment were profound, as it validated the semi-conservative model of DNA replication proposed by Watson and Crick. This finding helped clarify how genetic information is accurately copied and passed on during cell division, which is fundamental to molecular biology. The experiment laid the groundwork for future studies on DNA replication mechanisms, including insights into enzyme function such as that of DNA polymerase, and contributed significantly to our understanding of genetic inheritance, mutation processes, and biotechnology applications.

Related terms

Semi-conservative replication: A method of DNA replication where each new DNA molecule consists of one old strand and one new strand.

DNA polymerase: An enzyme responsible for synthesizing new DNA strands by adding nucleotides complementary to the template strand during replication.

N15 and N14 isotopes: Isotopes of nitrogen used in the Meselson-Stahl experiment to distinguish between old and newly synthesized DNA strands based on their density.