Question

→a) Describe the experiment conducted by F. Griffith in 1928 with Streptococcus pneumoniae and write the conclusions he arrived at.
→b) State the contribution of Avery, MacLeod and McCarty in providing biochemical nature to the results as obtained by Griffith.

Answer 1

• Griffith - transforming principle

• Macleod, mccCarty, ostwald avery - DNA heriditary material.

Experiment conducted by Griffith:

• Griffith in a series of experiment conducted over streptococcus pnemoniae, bacteria were grown on a culture plate ,some produce shiny colonies (S) while some produce rough colonies (R)

• this was because the smooth strain were able to synthesise a mucous polysacchride coat while R strain does not.

• mice infected with S strain died due to pneumonia while mice infected with R strain do not devlop pneumonia

• when injected with a mixture of heat killed S and live R bacteria the mice died

• he concluded that R strain transformed into S strain "transforming principle" and became virulet but at that stage he was not clear about the biochemical nature of genetic material.

biochemical investigation of macleod, mcCarty, ostwald avery :

• they purified DNA, proteins and RNA from heat killed S - strain and found DNA alone was able to transform R-strain to S- strain.