In a molecule of DNA, hydrogen bonds form between

A) adenine and cytosine

B) guanine and adenine.

C) adenine and uracil.

D) cytosine and thymine.

E) thymine and adenine.

E) Thymine and adenine

Explanation:

DNA or deoxyribonucleic acid has three parts - phosphate group, a nitrogenous base, deoxyribose sugar (5 carbon sugar). There are four types of nitrogenous bases. These are adenine, guanine, cytosine, and thymine. The adenine and guanine are purine and guanine, cytosine and thymine are pyrimidine bases. In the DNA molecule, phosphate groups face outside while the nitrogenous bases face towards the inner side. Each nitrogen bases joined together by 2 or 3 hydrogen bonds. Adenine and thymine are joined by 2 hydrogen bonds, guanine and cytosine are joined by three hydrogen bonds. The T always pairs with A and G pairs with C. The one purine pairs with one pyrimidine by hydrogen bonds. A single DNA molecule has more than 100 million base pairs.