AP BIOLOGY

Detailed explanation-1: -Hydrogen bond (H-bond) binds the nitrogen bases between the two strands of DNA. There are two H-bonds between A and T; three H-bonds between G and C.

Detailed explanation-2: -Within a molecule of DNA, pairs of bases are chemically bonded together by hydrogen bonds. These bonds hold the two strands of the molecule together. Bases pair up with each other in a consistent way, and this process is called complementary base pairing, or Watson-Crick base pairing.

Detailed explanation-3: -In addition to holding the DNA strands together, the hydrogen bonding between the complementary bases also sequester the bases in the interior of the double helix. Therefore, the hydrogen bonding between the bases reinforces the hydrophobic effects that stabilize the DNA.

Detailed explanation-4: -While carbon always makes four bonds to other atoms, nitrogen makes three real, covalent bonds and has an extra pair of electrons. This pair makes the nitrogen slightly negative so it can be attracted to hydrogen and form a weak hydrogen bond.