AP BIOLOGY

Detailed explanation-1: -Uracil is present only in RNA, whereas thymine is present only in DNA. Thus, thymine is the nitrogenous base which is not present in RNA.

Detailed explanation-2: -In RNA, the base thymine is not found and is instead replaced by a different base called uracil, abbreviated U. The other three bases are present in both DNA and RNA.

Detailed explanation-3: -Thus, the tRNA molecule does not contain a codon.

Detailed explanation-4: -Uracil is one of these bases. However, since mRNA is relatively short-lived and any potential faults don’t result in any lasting damage, RNA employs uracil because the instability doesn’t matter as much for RNA. Thymine is also quickly oxidized. The thymine in the nucleus is shielded from oxygen.

Detailed explanation-5: -DNA contains four bases which are adenine (A), guanine (G), cytosine (C) and thymine (T). RNA also contains four bases, the first three bases are same as in DNA but the fourth one is uracil (U).