Question

Identify the molecules with 4 double bonds with 2 Nitrogen atoms and 4 double bonds with 5 Nitrogen atoms in the following respectively.

• A. Thymine, Adenine
• B. Uracil, Guanine
• C. Adenine, Uracil
• D. Cytosine, Adenine

Hint:

Pyrimidines (Cytosine/Thymine/Uracil) have one ring (2 N); Purines (Adenine/Guanine) have two rings (4+ N).

Answer 1

The Correct Option is D

Step 1: Understand the question.
We need two molecules: one ring with 2 nitrogen atoms and one ring with 5 nitrogen atoms. These are nitrogenous bases, so we recall how many nitrogen atoms each base has.

Step 2: Sort bases into two families.
Pyrimidines (cytosine, thymine, uracil) have a single ring with 2 nitrogen atoms. Purines (adenine, guanine) have a double ring with more nitrogen atoms.

Step 3: Find the base with 2 nitrogen atoms.
Among the pyrimidines, cytosine has 2 nitrogen atoms in its single ring. So the first molecule should be cytosine.

Step 4: Find the base with 5 nitrogen atoms.
Among the purines, adenine has 5 nitrogen atoms (4 in its double ring plus one amino nitrogen). So the second molecule should be adenine.

Step 5: Match with the options.
We need the pair cytosine then adenine. Only one option gives this pairing.

Step 6: Final answer.
The pair is Cytosine and Adenine.
\[ \boxed{\text{Cytosine, Adenine}} \]