a-t base pairs in a dna double helixare chemically distinct from G-C base pairs. form three hydrogen bonds with each other. are more heat stable than G-C base pairs. are not accessible to DNA binding proteins. are of a different length than G-C base pairs.

A-T base pairs in a DNI double helix are chemically distinct from G-C base pairs.

Explanation:

Nitrogenated bases that form nucleic acids correspond to purines and pyrimidines. Adenine and guanine derive from purines, while Thymine and Citocine derive from Pyrimidines.

In the DNA molecule, Adenine (Purine) always form pairs with Timine (Pyrimidine), while Guanine (Purin) form pairs with Cytosine. Two hydrogen bonds unite the pair A-T, while three of them unite the pair G-C.

The structure of these bases is different hence, the chemical structure of the pairs is also different.