Question

Describe the Meselson-Stahl experiment. Include their hypotheses, experimental design, results, and conclusions.

Answer 1

1. The formation of new DNA where one strand is parental and the other one synthesized is new strand, is known as semi-conservative replication of DNA. Watson and Crick also proposed that replication of DNA molecule is semi-conservative.

2. Meselson and Stahl grew Escherichia coli (E. coli) bacteria in N15 medium (heavy isotope of Nitrogen) for several generations so that all their DNA strands may become labelled with N15.

3.Then the E coli were transferred to a medium containing normal nitrogen (N14).

4. They were allowed to replicate and their DNA was extracted for analysis by cesium chloride (CsCl) gradient centrifugation.

5. After analysis it was found that the DNA extracted from the E coli grown on N15 settled at the bottom of the tube; the DNA of E coli grown on N14 was found on the upper side of the tube.

6. Interestingly the DNA of the E coli which were transferred from N15 to N14, occupied the intermediate position.

7. It means that this type of DNA has one strand containing N15 and the other strand containing N14.

8.This proves DNA is semi-conservative.