AIIMS 2018 Chemistry Nucleic Acids MCQ Question

Option A correctly depicts the structure of guanine, which is characterized by its two fused rings and the presence of five nitrogen atoms within its molecular framework, consistent with its classification as a purine base. Other options fail to represent the specific arrangement of atoms and rings that define guanine; for instance, they may show incorrect ring structures or an inaccurate number of nitrogen atoms, leading to misidentification of the nucleobase. Understanding the structural features of nucleobases like guanine is crucial for grasping their roles in DNA and RNA, particularly in base pairing and genetic coding.