Coenzyme NAD+ is:
Correct answer: B. One adenine nucleotide and one nicotinamide nucleotide
- A. Two adenine nucleotides
- B. One adenine nucleotide and one nicotinamide nucleotide
- C. One guanine nucleotide and one cytosine nucleotide
- D. Two nicotinamide nucleotides
Explanation
The coenzyme NAD⁺ (nicotinamide adenine dinucleotide) is made up of two nucleotides joined by their phosphate groups. One nucleotide contains the adenine base, and the other contains nicotinamide, which is derived from vitamin B₃ (niacin). The nicotinamide part is responsible for accepting and donating electrons during redox (oxidation-reduction) reactions, while the adenine part provides structural support and helps the molecule bind to enzymes. Thus, NAD⁺ functions as an essential electron carrier in metabolic pathways such as glycolysis, the Krebs cycle, and oxidative phosphorylation.
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Cellular respiration explains how cells release energy from glucose through glycolysis, the link reaction, Krebs cycle and electron transport chain. It includes ATP production, substrate-level and oxidative phosphorylation, aerobic versus anaerobic respiration, and the roles of mitochondria, oxygen and fermentation in energy transfer.
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