AP BIOLOGY

Detailed explanation-1: -Uracil (U) is one of the four nucleotide bases in RNA, with the other three being adenine (A), cytosine (C) and guanine (G). In RNA, uracil pairs with adenine. In a DNA molecule, the nucleotide thymine (T) is used in place of uracil.

Detailed explanation-2: -Adenine pairs with thymine in DNA or uracil in RNA. Adenine creates two hydrogen bones with either thymine or uracil because it has two nitrogen atoms in its ring that can form hydrogen bonds. Guanine binds with cytosine in DNA and RNA and forms three hydrogen bonds.

Detailed explanation-3: -Adenine-uracil base pairs, or AU base pairs, are held together by 2 hydrogen bonds. Guanine-cytosine base pairs, or GC base pairs, are held together by 3 hydrogen bonds. The hydrogen bond donors and acceptors are labeled on the bases. The hydrogen bond donors are all NH groups.

Detailed explanation-4: -Neither DNA nor RNA base pairs uracil with guanine. Guanine base pairs with a pyrimidine called cytosine. The conformation of guanine does not allow it to form hydrogen bonds with uracil. Uracil base pairs with the purine base adenine.

Detailed explanation-5: -Between the bases of adenine and guanine, two hydrogen bonds form. The first is found between the lone pair electrons of uracil’s oxygen and the hydrogen of the adenine base. Another is present between the lone pair electrons of adenine’s nitrogen and the hydrogen of the uracil base.