Biochemistry Vitamins and Cofactors 1 — Questions and Answers
Question 1: Thiamine (Vitamin B1) deficiency causes which neurological and cardiovascular condition?
- Pellagra
- Beriberi (Correct answer)
- Scurvy
- Rickets
Correct answer: Beriberi
Thiamine deficiency causes beriberi, characterized by peripheral neuropathy (dry beriberi) or cardiovascular dysfunction (wet beriberi), due to impaired pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase.
Question 2: Niacin (Vitamin B3) is a precursor for which essential electron carrier coenzymes?
- FAD and FMN
- NAD⁺ and NADP⁺ (Correct answer)
- Coenzyme A and acetyl-CoA
- Pyridoxal phosphate and pyridoxamine
Correct answer: NAD⁺ and NADP⁺
Niacin (nicotinic acid/nicotinamide) is the precursor for NAD⁺ and NADP⁺, which are crucial electron carriers in oxidative metabolism and anabolic reactions respectively.
Question 3: Biotin serves as a cofactor for carboxylase enzymes by acting as a carrier of:
- Acyl groups
- Amino groups
- CO₂ (carboxyl groups) (Correct answer)
- Methyl groups
Correct answer: CO₂ (carboxyl groups)
Biotin is covalently attached to carboxylase enzymes and serves as a mobile carboxyl group carrier, transferring CO₂ in ATP-dependent carboxylation reactions such as those catalyzed by pyruvate carboxylase and ACC.
Question 4: Vitamin B12 (cobalamin) is required for which two reactions in humans?
- Fatty acid synthesis and glycolysis
- Methionine synthesis and methylmalonyl-CoA mutase reaction (Correct answer)
- DNA replication and RNA transcription
- Heme synthesis and bilirubin metabolism
Correct answer: Methionine synthesis and methylmalonyl-CoA mutase reaction
Cobalamin is required for methionine synthase (converting homocysteine to methionine) and methylmalonyl-CoA mutase (converting methylmalonyl-CoA to succinyl-CoA) in the metabolism of odd-chain fatty acids and some amino acids.
Question 5: Pyridoxal phosphate (PLP), the active form of Vitamin B6, is a cofactor for which class of enzymes?
- Oxidoreductases only
- Aminotransferases (transaminases) and other amino acid-metabolizing enzymes (Correct answer)
- Carboxylases
- Kinases
Correct answer: Aminotransferases (transaminases) and other amino acid-metabolizing enzymes
PLP forms a Schiff base with amino acid substrates and is essential for aminotransferases, amino acid decarboxylases, and many other enzymes involved in amino acid metabolism.
Question 6: Riboflavin (Vitamin B2) is the precursor for which two coenzymes?
- NAD⁺ and NADP⁺
- CoA and acyl-CoA
- FAD and FMN (Correct answer)
- Biotin and lipoic acid
Correct answer: FAD and FMN
Riboflavin is the precursor for flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which serve as prosthetic groups for flavoenzymes in oxidative metabolism.
Biochemistry Vitamins and Cofactors 1
Thiamine (Vitamin B1) deficiency causes which neurological and cardiovascular condition?