When did Alfred Hershey make his discovery?

Answer 1

Alfred Hershey and Martha Chase did an experiment in 1952 confirming that DNA is genetic material instead of protein. It was previously proven by Griffith in 1928 and then by Avery, McCarty, and MacLeod, but lingering doubts remained because it was previously believed that DNA didn't have the diversity to be hereditary material (Levene, whose status in the science world at that time was akin to that of a rock star, hypothesized that the 4 nucleotides occurred in equal quantities, and repeated in this tetranucleotide pattern - and you don't question a rock star).

Hershey and Chase's experiment utilized a bacteriophage (a type of virus that infects bacteria, whose name means bacteria-eater) called T2 in their experiment because it's basically made up of a bit of DNA (some viruses carry RNA) and a protective protein coat, which was what was previously believed to be the genetic material as previously mentioned. Also, they knew that T2 could quickly 'reproduce' through its host cell (Escherichia coli - the normal kind) and have many copies released.

They used a radioactive isotope of sulfur to tag protein in one batch of T2 and a radioactive isotope of phosphorus to tag DNA in another batch (there was no sulfur in the DNA and likewise no phosphorus in the protein). They let each infect separate samples of E. coli - whatever T2 injected into E. coli had to be the genetic material because that's what was capable of 'reprogramming' the bacteria.

They took the mixtures of T2 and E. coli and blended it to free the T2 leftovers from the E. coli's walls. They then centrifuged (spun it really fast to separate the substances by density) the mixtures. The T2 parts where lighter and thus would be suspended in the liquid, but the E. coli was heavier and would form a pellet on the bottom of the test tube. They would then measure the radioactivity of the liquid and pellet.

They tested the radioactive sulfur (protein) experiment and found that, surprise surprise, the pellet was NOT radioactive, but the liquid was. This meant that it wasn't the protein that infected the E. coli.

They tested the radioactive phosphorus (DNA) experiment and found that the liquid was NOT radioactive but the pellet WAS. This meant that DNA was the hereditary material, NOT protein.

If that wasn't enough, Hershey and Chase went on and returned the radioactive-phosphorus-T2-infected E. coli to a culture medium of more E. coli and let nature run its course. They found that the E. coli released T2s that contained traces of radioactive phosphorus, even further indicating that DNA was the genetic material, not protein.

They proved, at least for viruses, that DNA was the genetic material - a complete counter to the popular belief that protein was the genetic material. Then Chargaff came along and completely shredded Levene's tetranucleotide hypothesis. :)

Answer 2

Milton Hershey was the man who created and founded the world-famous Hershey Chocolate Company. He was also very involved in cahrity work, and created the town of Hershey, PA along with the Hershey School for under-privledged children.

Answer 3

We know DNA (not protein) is the genetic material of life.

Answer 4

discover the Deoxyribonucleic acid(DNA)

Answer 5

1952

Answer 6

chirurgie