AP BIOLOGY

Detailed explanation-1: -The first figure-a GC base-pair is having three hydrogen bonds, and the second-an AT base pair with two hydrogen bonds. The non-covalent hydrogen bonds between the bases are represented in dashed lines.

Detailed explanation-2: -The Adenine-Thymine base pair is held together by 2 hydrogen bonds while the Guanine-Cytosine base pair is held together by 3 hydrogen bonds. That is also the reason why the two strands of a DNA molecule can be separated more easily at sections that are densely populated by A-T base pairs.

Detailed explanation-3: -An A-T DNA base pair has two hydrogen bonds holding it together. A G-C DNA base pair has three hydrogen bonds. These hydrogen bonds work to hold the two strands of DNA together, and also help ensure the bases pair up correctly. Because of this, G-C bonds are generally stronger than A-T.

Detailed explanation-4: -Guanine and thymine are similarly incompatible. A always pairs with T and G always pairs with C because these are the only combinations that allow for hydrogen bonding to occur, given the spatial constraints of the double helix, which requires there to be one purine and one pyrimidine in each base pair.

Detailed explanation-5: -Two nitrogen-containing bases (or nucleotides) that pair together to form the structure of DNA. The four bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T). These bases form specific pairs (A with T, and G with C).