2003 AIPMT BiomoleculesNucleic Acids: Structure of DNA Easy Question 56 of 67 in Biomolecules

Chargaff's rule states that in an organism : -

A Amount of adenine (A) is equal to that of thymine (T) and the amount of guanine (G) is equal to that of cytosine (C)
B Amount of adenine (A) is equal to that of guanine (G) and the amount of thymine (T) is equal to that of cytosine (C)
C Amount of adenine (A) is equal to that of cytosine (C) and the amount of thymine (T) is equal to that of guanine (G)
D Amounts of all bases are equal

The answer is A.

Solution

Erwin Chargaff found that in double stranded DNA, the amount of adenine is always equal to that of thymine (A = T), and the amount of guanine is always equal to that of cytosine (G = C).
So purines = pyrimidines: A + G = T + C.
These rules are explained by the Watson–Crick model, in which A always pairs with T (two hydrogen bonds) and G always pairs with C (three hydrogen bonds).
The amounts of all four bases are not equal; the ratio (A + T)/(G + C) differs from species to species.
So Chargaff's rule states that A = T and G = C.

Concept Chargaff's base pairing rule

Biomolecules in past papers

67 questions from this chapter have appeared across 25 exam years.