Question

The pyrimidine bases present in DNA are:

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

Hint:

To remember the classification easily, use the mnemonic: "CUT the PY" $\rightarrow$ Cytosine, Uracil, and Thymine are PYrimidines. Remember that Thymine is unique to DNA, and Uracil is unique to RNA.

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Nucleic acids like DNA and RNA contain nitrogenous bases, which are broadly classified into two categories based on their chemical ring structures: purines and pyrimidines.

Step 2: Key Formula or Approach:
Purines possess a double-ring structure and include Adenine (A) and Guanine (G).
Pyrimidines possess a single six-membered heterocyclic ring structure and include Cytosine (C), Thymine (T), and Uracil (U).

Step 3: Detailed Explanation:
The distribution of these nitrogenous bases varies between DNA and RNA:
In DNA, the purines are Adenine and Guanine, while the pyrimidines are Cytosine and Thymine.
In RNA, Thymine is replaced by Uracil, meaning its pyrimidines are Cytosine and Uracil.
The question explicitly asks for the pyrimidine bases present in DNA, which are Cytosine and Thymine.

Step 4: Final Answer:
The pyrimidine bases present in DNA are Cytosine and Thymine.