AP BIOLOGY

Detailed explanation-1: -Adenine (A), Thymine (T), Guanine (G) and Cytosine (C) are four types of nitrogen bases. These 4 Nitrogenous bases pair together in the following way: A with T, and C with G. These base pairs are essential for the DNA’s double helix structure, which resembles a twisted ladder.

Detailed explanation-2: -Each nucleotide is composed of a nitrogenous base, a five-carbon sugar (deoxyribose), and a phosphate group. There are four nitrogenous bases in DNA, two purines (adenine and guanine) and two pyrimidines (cytosine and thymine).

Detailed explanation-3: -Molecules called nucleotides, on opposite strands of the DNA double helix, that form chemical bonds with one another. These chemical bonds act like rungs in a ladder and help hold the two strands of DNA together.

Detailed explanation-4: -The sugar-phosphate backbones of the DNA strands make up the outside of the helix, while the nitrogenous bases are found on the inside and form hydrogen-bonded pairs that hold the DNA strands together.

Detailed explanation-5: -The two strands are held together by hydrogen bonds between pairs of bases: adenine pairs with thymine, and cytosine pairs with guanine.