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#NAD+

6 public questions tagged with this topic.

RDT Basics

E. coli DNA ligase uses which cofactor?

DNA ligases catalyze phosphodiester bond formation via an enzyme-AMP intermediate requiring adenylation. The source of AMP differentiates ligase families. Bacteriophage T4 ligase and most eukaryotic ligases are ATP-dependent, cleaving ATP to AMP and pyrophosphate to activate the active-site lysine. In contrast, Escherichia coli DNA ligase and several other bacterial ligases are NAD+-dependent, using oxidized nicotinamide adenine dinucleotide as adenyl donor and releasing NMN. Both classes require divalent magnesium for catalysis. Recognizing cofactor specificity is essential for choosing buffers and understanding bacterial DNA replication, repair, and cloning enzymology.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

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Enzyme Kinetics

Which of the following coenzymes is derived from vitamin B3?

Nicotinamide adenine dinucleotide is the correct answer because it serves as the specific precursor, synthetic product, or metabolic intermediate described in this question. Biosynthetic pathways in Enzymes Basics follow precise enzymatic steps where specific substrates are converted to products through regulated metabolic reactions. Nicotinamide adenine dinucleotide occupies a key position in this metabolic pathway due to its chemical structure and reactivity. The other options (Thiamine pyrophosphate, Flavin adenine dinucleotide, and Pyridoxal phosphate) are involved in different biosynthetic routes, serve as precursors for different end products, or participate in unrelated metabolic conversions.

Ref: Lehninger Principles of Biochemistry, Nelson & Cox, 8th Ed., Ch. 6

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