Question

Why does A only pair with T?

Answer 1

DNA bases:

1. In contrast to thymine and cytosine, which are pyrimidines, adenine and guanine are purines.
2. A base pair, which consists of two nucleobases joined by hydrogen bonds, is the basic building block of double-stranded nucleic acids.
3. They contribute to the folded shape of both DNA and RNA and serve as the building blocks of the DNA double helix.

Purines are always combined with pyrimidines because:

1. The bonds between Adenine and Thymine create a similar shape as guanine and cytosine to accommodate the diameter of 2nm which is the pitch of the helix.
2. Purines can't combine with other purines due to double-ring structures.
3. The higher the bond specificity higher the stability and the bond will be stronger.
4. DNA hydrogen bond structures that cause only adenine to pair with thymine