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: Sort the bases.
Nitrogen bases come in two groups. Purines have a double ring and pyrimidines have a single ring.

Step 2: Name the pyrimidines.
The single ring pyrimidines are cytosine, thymine and uracil. The purines are adenine and guanine.

Step 3: Pick the pair for DNA.
DNA uses cytosine and thymine as its pyrimidines. Uracil is not in DNA; it shows up in RNA instead, taking thymine's place.

Step 4: Final choice.
So the pyrimidine bases in DNA are cytosine and thymine.
\[ \boxed{\text{Cytosine and Thymine}} \]