A Level Biology Practice Exam

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Purines are characterized as what kind of nitrogenous bases?

  1. Single-ringed

  2. Double-ringed

  3. Triple-ringed

  4. Quadruple-ringed

The correct answer is: Double-ringed

Purines are characterized as double-ringed nitrogenous bases. This structural feature is important because it distinguishes purines from pyrimidines, which have a single-ring structure. In the context of nucleic acids, purines include adenine (A) and guanine (G), both of which play critical roles in the formation of DNA and RNA. Their double-ring structure allows them to pair effectively with the single-ringed pyrimidines (cytosine, thymine, and uracil) during the processes of DNA replication and transcription, contributing to the stability and functionality of nucleic acid structures.

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