George Beadle and Edward Tatum

George Beadle and Edward Tatum rediscovered the work of another scientist, Garrod in 1940.

Beadle and Tatum used a very simple organism for their experiment. This organism was Neurospora, which is a fungus. Their experiment was all about showing a connection between enzyme and gene, so they gave the one gene one enzyme hypothesis.

Experiment.

Beadle and Tatum prepared two different kinds of cultural mediums, one was minimal media and the other was complete media.

Now, what are minimal media and culture media?

Minimal media is the minimum or essentials nutrients that are required for the growth of any normal organism, while complete media is the complete nutrients that can be used by both normal and abnormal (or imperfect) organisms.

In the case of Neurospora, Beadle, and Tatum used sugar, salts, and biotin etc as minimal medium while the complete nutrients contain sugar, salts, amino acids, vitamins, etc.
They placed the spores of Neurospora in both minimal medium and compete medium and they observed that spores of Neurospora show growth in both types of conditions.
Now, they expose the X-rays to Neurospora, and this induced mutation in the spores of Neurospora.
They again placed these mutant spores of Neurospora in both minimal medium and complete medium.
But this time, spores of Neurospora show growth only in complete medium and are not able to survive in minimal media.
They concluded that X-rays cause some kind of nutritional mutation.
Something must be missing in minimal media so the spores are unable to grow in minimal medium and die.
While that thing is present in the complete medium and because of this thing the spores of Neurospora in the complete medium are able to grow well.

Now, what is meant by nutritional mutation?

The nutritional mutants only survive in complete media and are unable to grow in minimal media because they have some kind of mutation in cells and are unable to prepare their food.

Now, this essential nutrient may be an amino acid or a vitamin because complete media contains both.

To answer this, they added vitamins in minimal media and observed the growth of spores. The spores did not show any growth.
Then they added amino acids in minimal media and this time spores of Neurospora show growth.

So, it was confirmed that the missing molecule was an amino acid.

Now, complete media have 20 types of amino acids and it’s time to answer what type an amino acid is not prepared by the spores of mutant Neurospora.

For this purpose, they added 20 different types of amino acids in 20 different test tubes of minimal media.
The mutant spores of Neurospora show growth in just the test tube which has minimal media plus arginine.
So it was confirmed that mutant spores of Neurospora were unable to make arginine and because of the deficiency of this arginine, they are unable to grow.

Conclusion.

Beadle and Tatum introduce one gene one enzyme hypothesis from their experiment.

According to them, one gene can produce just one kind of enzyme because the information for this enzyme is only present in that gene.
If we induce some mutations and the specific gene is not able to perform, then this enzyme will not be produced by the organism and eventually the death of that organism.

The concept of one gene one enzyme was not considered by the scientists because they found that enzymes are just a type of protein and not every protein is an enzyme.

They also found that some genes can make just polypeptides, not whole proteins.

However, the work of Beadle and Tatum is very helpful for scientists because they show a one-to-one relationship between genes and proteins.