Question

The composition, in mole fraction units, of one of the strands of a double helical DNA molecule is [A]=0.30 and [G]0.24. This strand is the reference strand.

a. What is the total [T] and [C] for the reference strand?
b. What is the total [A] and [G] for the complementary strand?
c. What is the total [T] for the complementary strand
d. What is the total (C) for the complementary strand?

Answer 1

Given the mole fraction of adenine and guanine in one strand of DNA, the complementary strand will have identical mole fractions for thymine and cytosine, respectively, due to the base-pairing rules of the DNA double helix, adhering to Chargaff's rule.

Step-by-step explanation:

In DNA, the bases adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). This is a consequence of the structure of the double helix and is referred to as Chargaff's rule, where the amount of A always equals T and the amount of G always equals C. Given the composition of one DNA strand with mole fractions [A]=0.30 and [G]=0.24, we can answer the following questions:

1. The total mole fraction of thymine [T] and cytosine [C] for the reference strand would be the same as that of their complementary bases. Thus, [T]=0.30 and [C]=0.24 since A pairs with T and G pairs with C in the double helix of DNA.
2. The total mole fraction of adenine [A] and guanine [G] for the complementary strand will also be equal to [T] and [C] respectively of the reference strand, so [A]=0.30 and [G]=0.24 on the complementary strand.
3. The total mole fraction of thymine [T] for the complementary strand is equal to the mole fraction of adenine [A] in the reference strand, indicating [T]=0.30.
4. The total mole fraction of cytosine [C] for the complementary strand is equal to the mole fraction of guanine [G] in the reference strand, indicating [C]=0.24.