Question

In: Biology

How was the chemical nature of the gene discovered?

Expert Solution

1) in 1869 - Miescher discovered nuclear material contained a substance that was acidic and high in Phosphorus. termed nuclein.

2) in 1928 - Griffith did experiment on Streptococcus pneumoniae: two types s type and r type

s type- virulent: caused lethal pneumonia

r type - non-virulent: doesn?t kill mice

he did following experiment-

strain injected effects blood analysis

r Type none dead no bacteria present

s Type all dead s Type present

killed s Type none dead no bacteria present

killed s Type + r Type all dead s Type present

so he conclude that something is present in s type which converts r type to s type. but he is not sure whether it is protein or the DNA.

upto 1940's it is believed that protein is the genetic material but

1944 - Avery, McLeod and McCarthy Proved that the transforming substance is DNA.

so they made a soluble cell extract from s Type and tested the ability to transform r Type into s Type.

they did 3 treatments

(a) one that destroys proteins = protease

(b) one that destroys RNA = RNAase

(c) one that destroys DNA = DNAase

and did the transformation experiment

Results

experiment condition Transformation of r type Transforming Substance

A. S extract alone YES No idea

B. S extract + protease YES NOT PROTEIN

C. S extract + RNAase YES NOT RNA

D. S extract + DNAase NO must be DNA

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