Question

Chargaff's Rules state that

a.adenine will always pair with guanine
b.thymine will always pair with cytosine
c.there are about equal numbers of cytosine and guanine
d.all of the choices are correct

Answer 1

In Chargaff's rules, adenine pairs with thymine, and cytosine pairs with guanine, leading to equal amounts of these complementary bases in DNA.

Step-by-step explanation:

The correct answer to the student's question is that there are about equal numbers of cytosine and guanine, and that adenine will always pair with thymine. This understanding is a direct result of Chargaff's rules, which state the following:

• The number of adenine (A) units is approximately equal to the number of thymine (T) units.
• The number of guanine (G) units is approximately equal to the number of cytosine (C) units.

Further, base pairing in DNA occurs between a purine and a pyrimidine: adenine (A) pairs with thymine (T), and cytosine (C) pairs with guanine (G). These pairings are due to the complementary nature of the bases and are stabilized by hydrogen bonds: two bonds between A and T, and three bonds between C and G.