Test: The Search for Genetic Material (NCERT) - NEET MCQ

The Meselson and Stahl experiment was an experiment to prove that DNA replication was semi-subsequently and it was first shown in Escherichia coli and subsequently in higher organisms, such as plants and human cells. Semi-conservative replication means that when the double stranded DNA helix was replicated, each pf the two double stranded DNA helices consisted of one strand coming from the parental helix and one is newly synthesised.

Hershey and Chase experiment is based on the fact that DNA contains phosphorus and similarly, sulphur is present in proteins but not in DNA. They incorporated radioactive isotope of phosphorus (³²P) into phage DNA and that of sulphur (³⁵S) into proteins of a separate phage culture. Viruses grown in the presence of radioactive phosphorus contained radioactive DNA but not radioactive protein because DNA contains phosphorus but proteins do not, Similarly, viruses grown on radioactive sulphur contain radioactive- protein but not-radioactive DNA because DNA does not contain sulphur.

Hershey and Chase concluded that DNA is the genetic material because only the DNA labeled with radioactive phosphorus entered the bacterial cells and directed the production of new viruses.

Sulfur is a component of certain amino acids in proteins but is not found in DNA. Therefore, viruses grown in the presence of radioactive sulfur had radioactive proteins but not radioactive DNA.

Radioactive phosphorus was used to label DNA because DNA contains phosphorus, while protein does not.