Question

Write 1-2 paragraphs explanation of the mechanism of transformation uncovered by Oswald Avery. Be sure to include proper in-text citation/referencing for each source (ex. research paper, news report, blog, etc.).  

Answer 1

Avery-MacLeod-McCarty experiment was carried out by Oswald Avery, Colin Macleod and Maclyn McCarty in 1944 that revelaed that DNA is the genetic material that causes transformation. Before that it was thought that protein is the genetic material.

In 1928,Frederick Griffith conduct experiments using Streptococcus pneumonia and mice in an attempt to develop vaccine for pneumonia. He used two strains of pneumonia: R strain and S strain.R strain are non virulent and have rough appearance whereas S strain are virulent and have smooth appearance due to sugar coat produced by bacteria. The series of experiments carried out by him are as follows:

a) When R strain was injected into mice , the mice survived

b) When S strain was injected into mice, the mice died

c) When heat killed S strain was injected into mice, the mice survived

d) When non virulent R strain was combined with heat killed S strain and injected into mice , the mice died because of pneumonia and blood sample also showed the presence of virulent S-strain.

This led him to conclude that R strain bacteria may have taken up so called transforming principle which transformed them into smooth and virulent S strain which killed the mice.

In 1944, Avery, MacLeod and McCarty conducted a series of biochemical experiments to identify the transforming principle. They purified the transforming material by degrading the other components enzymatically. The purified transforming material was analyzed for its identity:

a) It gave negative results for protein and positive result for DNA.

b) The chemical composition was similar to DNA

c) Protein and RNA degrading enzymes has less effect on transforming principle but DNAase degraded it.

This led them to conclude that transforming principle might be DNA.In 1945 , Avery was awarded prize by Royal society for his work on bacterial transformation.

Their work was ignored but was accepted decades later.