Which one among the following possess a double ringed structure?
Correct answer: B. Adenine
- A. Cytosine
- B. Adenine
- C. Uracil
- D. Thymine
Explanation
Purines, such as adenine and guanine, have a double-ringed structure - one hexagonal pyrimidine ring and an imidazole ring. Adenine is the correct option as it belongs to purines. Cytosine, uracil, and thymine are all single-ringed pyrimidines, making them incorrect options.
This question appeared on the ETEA MDCAT 2009 paper, which you can sit online with every answer explained.
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About Structure of DNA
DNA structure includes nucleotides made of deoxyribose, phosphate and nitrogenous bases, arranged in two antiparallel polynucleotide strands. Questions cover the double helix, phosphodiester and hydrogen bonds, complementary base pairing between adenine and thymine and between guanine and cytosine, and the significance of major and minor grooves.
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