Biochemistry Vitamins and Cofactors

Question 1

Thiamine (Vitamin B1) deficiency causes which neurological and cardiovascular condition?

Accepted Answer

Beriberi

Answer

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?

Accepted Answer

NAD⁺ and NADP⁺

Answer

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:

Accepted Answer

CO₂ (carboxyl groups)

Answer

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?

Accepted Answer

Methionine synthesis and methylmalonyl-CoA mutase reaction

Answer

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?

Accepted Answer

Aminotransferases (transaminases) and other amino acid-metabolizing enzymes

Answer

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.

Biochemistry Practice Test

Biochemistry Practice Test

Biochemistry Vitamins and Cofactors