Which nitrogenous base is present in $\mathrm{RNA}$ but not in $\mathrm{DNA}$?

• A. $\mathrm{Uracil}$
• B. $\mathrm{Thymine}$
• C. $\mathrm{Cytosine}$
• D. $\mathrm{Adenine}$

Answer: (A)

Verified step by step guidance

1. Understand the basic structure of nucleic acids: DNA and RNA are composed of nucleotides, each containing a sugar, a phosphate group, and a nitrogenous base.
2. Identify the nitrogenous bases in DNA: DNA contains four nitrogenous bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).
3. Identify the nitrogenous bases in RNA: RNA also contains four nitrogenous bases, but instead of Thymine, it contains Uracil (U). The bases in RNA are Adenine (A), Uracil (U), Cytosine (C), and Guanine (G).
4. Compare the bases in DNA and RNA: Notice that the only difference in the nitrogenous bases between DNA and RNA is that RNA contains Uracil instead of Thymine.
5. Conclude which base is unique to RNA: Since Uracil is present in RNA and not in DNA, it is the nitrogenous base that is unique to RNA.