Answer: Cytosine.
- A Cytosine
- B Adenine
- C Guanine
- D Xanthine
Correct answer: A. Cytosine
Explanation: Cytosine, thymine and uracil are pyrimidines (single-ring bases), whereas adenine and guanine are purines (double-ring bases).
Helicase unwinds the double helix at the replication fork; one new strand (leading) is synthesised continuously toward the fork, while the other (lagging) must be made in short, separate Okazaki fragments because DNA polymerase only adds nucleotides 5'→3'.
Concept context
DNA structure, replication, transcription, translation, the genetic code, and gene regulation (lac operon). The single most important chapter for NEET molecular biology.