How are the base-pairing rules different for $\mathrm{RNA}$ compared to $\mathrm{DNA}$?

• A. In $\mathrm{RNA}$, $A$ (adenine) pairs with $C$ (cytosine) instead of $U$ (uracil).
• B. In $\mathrm{RNA}$, $A$ (adenine) pairs with $U$ (uracil) instead of $T$ (thymine).
• C. In $\mathrm{RNA}$, $C$ (cytosine) pairs with $U$ (uracil) instead of $G$ (guanine).
• D. In $\mathrm{RNA}$, $G$ (guanine) pairs with $T$ (thymine) instead of $C$ (cytosine).

Answer: (B)

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 adenine (A), thymine (T), cytosine (C), and guanine (G).
3. Identify the nitrogenous bases in RNA: RNA contains adenine (A), uracil (U), cytosine (C), and guanine (G). Note that uracil replaces thymine in RNA.
4. Learn the base-pairing rules for DNA: In DNA, adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G).
5. Learn the base-pairing rules for RNA: In RNA, adenine pairs with uracil (A-U) and cytosine pairs with guanine (C-G). This is the key difference in base pairing between DNA and RNA.