Question

Erwin Chargaff is considered one of the pioneering scientists in the field of molecular biology. In one of his studies, Chargaff observed that a sample of human DNA contained approximately 30% adenine (A). Based on DNA structure, what are the expected percentages of the other nitrogenous bases in the sample?

Answer 1

A.

10% thymine, 40% cytosine

B.

20% thymine, 30% cytosine

C.

30% thymine, 20% cytosine

D.

40% thymine, 10% cytosine#

Answer:

30% thymine, 20% cytosine

Step-by-step explanation:

In a typical DNA double helix pyrimidine; Cytosine and thymine always pair with Purine ;Adenine and Guanine. This pairing ensure that the double helix of DNA is maintained by the presence of Hydrogen between these organic bases.

For correct pairing all adenine must pair with thymine,and all Cytosine with guanine.Therefore for this to occur if 30 % of adenine is present,the composition and number of thymine(30%) must be available.If this percentage is not available the pairing will not occur.

Like wise 20% Cytosine must be present because ,then same amount of Guanine molecule 20% in the DNA molecule. must be present Thus Guanine percentage is 20%.

This give a total of 100(60+40)

This based on the Erwin Chargaff stoichiometric ratio of 1:1 .This states that the percentage of adenine =thymine,and that of Guanine=Cytosine,in the DNA of living cells should be equal. Thus; [A]+[G]=[C]+[T]=1:1