Question

What are topological isomers of DNA?

A) DNA molecules with different base compositions
B) DNA molecules with the same sequence but different conformations
C) DNA molecules with different numbers of hydrogen bonds
D) DNA molecules with mismatched base pairs

Answer 1

Topological isomers of DNA are DNA molecules with the same sequence but different conformations, such as B-DNA, A-DNA, and Z-DNA forms. The correct option is B.

Step-by-step explanation:

Topological isomers of DNA are DNA molecules with the same sequence but different conformations. These isomers can occur due to the structural flexibility of the DNA double helix, which allows for various spatial arrangements without altering the base pair sequence.

There are several DNA conformations, including the well-known B-DNA form, the A-DNA form, and the Z-DNA form, each with a unique topology. It's important to note that adenine (A) always pairs with thymine (T), and cytosine (C) always pairs with guanine (G).

The complementary nature of these base pairs is crucial for the structure of DNA as they form hydrogen bonds: A and T form two hydrogen bonds, while C and G form three. The correct answer to the student's question is B) DNA molecules with the same sequence but different conformations.