Answer: Adenine.
- A Adenine
- B Guanine
- C Cytosine
- D Uracil
Correct answer: A. Adenine
Explanation: Adenine (a purine) pairs with thymine via two hydrogen bonds; guanine pairs with cytosine via three hydrogen bonds.
Two amino acids join via a condensation reaction: the carboxyl -OH of one and an amine -H of the other are eliminated as water, leaving a peptide bond (-CO-NH-) linking them into a dipeptide; repeating this builds a full protein chain.
Concept context
The chemistry of life: carbohydrates, proteins, lipids, nucleic acids, enzymes, and vitamins. Understand their structures, classification, and biological functions. Highly relevant for NEET and Class 12 board exams.