In the Hershey and Chase experiment that helped confirm that DNA, not protein, was the hereditary material, what was the key finding?
The Correct Answer and Explanation is:
The key finding of the Hershey and Chase experiment, conducted in 1952, was that DNA, not protein, is the hereditary material. This discovery was pivotal in confirming the role of DNA in heredity and laid the foundation for our understanding of molecular genetics.
Explanation:
Before the Hershey and Chase experiment, scientists were unsure whether DNA or proteins carried genetic information. Proteins were believed to be the likely candidates due to their complexity and variety of functions in the cell, whereas DNA was considered too simple because it was composed of only four nucleotides.
Hershey and Chase used the bacteriophage T2, a virus that infects bacteria, to test this. Bacteriophages consist of two components: a protein coat and DNA inside. They hypothesized that if DNA were the genetic material, only the DNA would enter the bacterial cell and direct the creation of new phages.
The experiment involved labeling the protein and DNA of the phage with different radioactive isotopes. They used sulfur-35 (³⁵S) to label the proteins (because sulfur is found in proteins but not in DNA) and phosphorus-32 (³²P) to label the DNA (because phosphorus is a component of DNA but not proteins). The labeled bacteriophages were then allowed to infect E. coli bacteria.
After infection, Hershey and Chase used a blender to separate the phage protein coats (which remained outside the bacterial cell) from the bacterial cells (which contained the genetic material). They found that only the ³²P-labeled DNA entered the bacterial cells and was used to produce new phages, whereas the ³⁵S-labeled protein remained outside the bacteria. This indicated that DNA, not protein, was the material that carried genetic information and directed the synthesis of new viral particles.
Their experiment provided strong evidence that DNA was the molecule responsible for heredity, overturning the prevailing belief that proteins were the genetic material. This discovery was a crucial step toward understanding how genetic information is transmitted in living organisms.