Which of these nitrogenous bases is NOT a part of RNA?

Analyze the question: You're asked which nitrogenous base is not found in RNA. So we need to recall the bases of RNA and find the odd one out.

Concept: Nucleic acids (DNA and RNA) are built from nucleotides. Each nucleotide has a sugar, a phosphate group, and a nitrogenous base.

| Nucleic acid | Sugar | Bases | |---|---|---| | DNA | Deoxyribose | Adenine, Guanine, Cytosine, Thymine | | RNA | Ribose | Adenine, Guanine, Cytosine, Uracil |

The only difference in bases is that DNA uses thymine, while RNA uses uracil in its place.

Solution, checking each option:

• A. Adenine: found in RNA ✔
• B. Cytosine: found in RNA ✔
• C. Guanine: found in RNA ✔
• D. Thymine: found only in DNA, not in RNA ✘
• E. Uracil: found in RNA ✔

Answer: The base that is not part of RNA is Thymine, which is option D.

Tip: Remember "U is in RNA, T is in DNA." Another trick: the letter T in Thymine goes with DNA, while Uracil is Unique to RNA. In base pairing, adenine pairs with thymine in DNA, but with uracil when RNA is involved (for example, during transcription).