Question

The nucleic acid base found in mRNA but not in DNA is

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

Hint:

DNA bases: A-G-C-T.
RNA bases: A-G-C-U.
Remember: RNA says "U" are not like me!

Answer 1

The Correct Option is D

Step 1: Understanding the Question:
The question asks to identify the nitrogenous base that is unique to RNA (like mRNA) and is absent from the DNA double helix.
Detailed Explanation:

• Bases in DNA:
Deoxyribonucleic acid (DNA) contains four nitrogenous bases: Adenine (A), Guanine (G), Cytosine (C), and Thymine (T).
A pairs with T, and G pairs with C.

• Bases in RNA:
Ribonucleic acid (RNA), including messenger RNA (mRNA), also contains four bases.
Three are the same as in DNA: Adenine, Guanine, and Cytosine.
However, instead of Thymine, RNA contains Uracil (U).

• Structural Difference:
Uracil is structurally very similar to Thymine. Thymine is essentially a methylated version of Uracil (also called $5$-methyluracil).
During transcription, when mRNA is synthesized from a DNA template, Uracil is incorporated wherever the DNA template has an Adenine.

• Why Uracil?
Uracil is less energetically expensive for the cell to produce than Thymine. Since RNA is often temporary and constantly broken down, using Uracil is more efficient. DNA uses Thymine because it is more stable and less prone to mutations, which is critical for the long-term storage of genetic information.

Step 3: Final Answer:
The base Uracil is found in mRNA but is absent in DNA.