Question

What type of nitrogenous base is Uracil and what is its structure?

• A. Purine base \(\rightarrow\) 2 rings, structure similar to adenine
• B. Pyrimidine base \(\rightarrow\) 1 ring, 2 keto groups at C2 & C4; structure similar to thymine but without \(-CH_{3}\) at C5
• C. Purine base \(\rightarrow\) 1 ring, 3 keto groups
• D. Pyrimidine base \(\rightarrow\) 2 rings, 1 keto group

Hint:

Remember the nitrogenous bases: \[ \boxed{ \begin{aligned} \text{Purines} &: A,\;G\\ \text{Pyrimidines} &: C,\;T,\;U \end{aligned} } \] Uracil is present only in RNA and is structurally similar to thymine, except that it lacks the methyl (\(-CH_3\)) group at C5.

Answer 1

The Correct Option is B

Uracil is a pyrimidine nitrogenous base found exclusively in RNA, replacing thymine. Its structure is a six-membered ring containing two nitrogen atoms with carbonyl ($C=O$) groups at positions 2 and 4, and it lacks the methyl group present at position 5 in thymine; it base-pairs with adenine.