AP BIOLOGY

Detailed explanation-1: -Adenine always bonds with thymine, and cytosine always bonds with guanine. The bonding causes the two strands to spiral around each other in a shape called a double helix.

Detailed explanation-2: -In base pairing, adenine always pairs with thymine, and guanine always pairs with cytosine. Source: definition from the National Human Genome Research Institute (NHGRI) Glossary of Genetic Terms. In addition to the letters A, C, T, and G, a number of other abbreviations can be used to represent the nucleotide bases.

Detailed explanation-3: -Assertion :The two strands of DNA are complementary to each other. Reason: Adenine specifically forms hydrogen bonds with guanine whereas cytosine forms hydrogen bonds with thymine.

Detailed explanation-4: -Adenine always pairs with thymine through two hydrogen bonds in DNA. Similarly, adenine pairs with uracil through two hydrogen bonds in RNA and guanine always pairs with cytosine through three hydrogen bonds in both the nucleic acids.

Detailed explanation-5: -Under normal circumstances, the nitrogen-containing bases adenine (A) and thymine (T) pair together, and cytosine (C) and guanine (G) pair together.