Gene - Polypeptide Hypothesis

Question 1

Describe the contribution of Garrod (20th C., British doctor)

Answer 1

First to hypothesize that a gene directs the production of one enzyme.

Studied families with the disorder Alkaptonuria, in which the urine appears black due to the chemical alkapton, which turns black in the present of oxygen. He hypothesized that individuals with this disorder have a defective enzyme that does not metabolize alkapton.

Question 2

Describe the contribution of Beadle and Tatum

Answer 2

Used the bread mould Neurospora crassa. Worked with mutant strains, placing them in a controlled medium. By adding or deleting certain molecules, mutant strains would or would not grow. They determined which product was accumulating and concluded the enzyme after it was the defective one.

Question 3

Describe the Beadle and Tatum experiment

Answer 3

Neurospora in minimal medium (simple inorganic salts, sugars, and one of the B vitamins) would grow. When zapped with X-rays/UV the mould became defective and would not grow in minimal medium. The zapped mould still grew in a complete medium.

Then, they took the mutant mould and placed them in minimal media with one extra nutrient to find out which amino acid was not able to be synthesized. The mould grew in the medium with argenine, therefore the argenine pathway was destroyed. In the pathway for the creation of argenine, ornithine accumulated, so the enzyme immediately after it was defective.

They concluded that a gene codes for the production of one enzyme.

Question 4

Describe the contribution of Vernon Ingram

Answer 4

Studied sickle cell anemia and found that a substitution with one amino acid would cause a deformation in protein structure.

Discovered that genes code not only for enzymes but other proteins. Some proteins consist of more than one polypeptide chain, each chain is controlled by a different gene.