Question

If the dna of a species has the mole fraction of g+c is 0.48,the mole fraction of a will be

Answer 1

T+A = 1- (G+C)
= 1- 0.48
. = 0.52

NUMBER OF T = NUMBER OF A
This is because bases T are attached to bases A and bases G are attached to bases C in a DNA strand.

So A = 0.52/2 = 0.26

Answer 2

The mole fraction of A will be 0.26 following the Chargaff's rule.

Explanation:

According to the Chargaff's rule

• The total mole fraction of all the four nitrogenous bases that are present in DNA is equal to one.

It is given that G + C = 0.48

Thus mole fraction of A + T = 1 - 0.48 = 0.52

Now, consider the pairing of the nitrogenous bases in DNA

• A pairs with T with double hydrogen bonds
• G pairs with C with triple hydrogen bonds

Thus, the mole fraction of G = mole fraction of C

and, mole fraction of A = mole fraction of T

So, mole fraction of A = $\frac{0.52}{2}$ = 0.26