MCQ (Protein, Vitamin and Enzyme)

MCQ for 1st year of medical students In protein structure, B sheet is an example of: a. primary structure. b. secondary structure. c. tertiary structure. d. quaternary structure. Glutamate, tryptophan & arginine can form the tripeptide: a. glutamate lytryptophany arginine. b. glutamate tryptophanarginine. c. glutamyl tryptophylarginine. d. glutamyl tryptophyl anginyl. Hydroxyl containing amino acid is: a. tryptophan b. arginine. c. serine. d. methionine. About denaturation of proteins: a. it is accompanied by hydrolysis of peptide bonds. b. it results in unfolding of secondary & tertiary structure. c. reversible denaturation causes permanent disorder of protein. d. when denaturing agent is removed in irreversible denaturation, proteins re Disulfide bond is formed from: a. two methionine residues. b. two arginine residues. c. two serine residues. d. two cysteine residues. Lipoprotein is an example of: a. Simple protein. b. compound protein c. derived protein d. amino acid Alanine is: a. essential amino acid. b. non essential amino acid c. non proteinogenic amino acid d. glucogenic amino acid. One of the following amino acids is semi-essential: a. serine. b. tryptophan. c. glycine. d. arginine Sickle cell anemia (HbS) results from the replacement of glutamate by: a. valine at position 6 in alpha chain b. valine at position 6 in beta chain c. lysine at position 6 in alpha chain d. lysine at position 6 in beta chain. Alpha-helix is stabilized by: a. ionic bonds b. disulfide bonds c. hydrophobic bonds d. hydrogen bonds Fetal hemoglobin contains: a. two alpha & two delta chains b. two alpha & two gamma chains c. two alpha & two beta chains d. two alpha chains only A protein rich in cysteine is: a. collagen b. keratin c. hemoglobin d. myoglobin A peptide bond: a. has a partial double bond character b. is non-polar c. occurs most commonly in cis configuration d. is stable to heating in strong acids About myoglobin: a. is a hemeprotein present in liver & kidneys b. functions both as a reservoir for oxygen & as an oxygen carrier c. consists of a four polypeptide chain d. has a sigmoidal oxygen dissociation curve Hemoglobin A: a. has more affinity for oxygen than myoglobin. b. can bind one oxygen molecule only. c. has a hyperbolic oxygen dissociation curve. d. is composed of 4 polypeptide chains (2 alpha & 2 beta chains) Optically inactive amino acid is: a. histidine. b. aspartate. c. glycine. d. isoleucine Phenylalanine is: a. ketogenic amino acid only. b. glucogenic amino acid only. c. both glucogenic & ketogenic amino acids. d. non essential amino acid About collagen: a. polypeptides are stabilized by disulfide bonds. b. it's a rigid structure in which two polypeptides are wound around one another. c. about 33% of amino acids are glycine. d. hydroxylation of collagen requires the presence of vitamin K. Zymogens: a. are enzymes that catalyze the same chemical reaction. b. are substances that decrease the rate of an enzyme-catalyzed reaction. c. are inactive precursors of an enzyme. d. are enzyme modulators. Creatine kinase (CK) is an example of: a. zymogen b. proenzyme c. isoenzyme d. ribozyme Sulfanilamide is a competitive inhibitor to: a. malonate b. succinate c. p-aminobenzoic acid d. lactose Any change of pH below or above the optimum pH: a. increases enzyme activity b. decreases enzyme activity c. has no change in the enzyme activity d. does not change the ionization state Optimum temperature of all enzymes in humans is: a. below 35°C b. above 40°C c. between 35°C & 40°C d. between 30°C & 40°C Low Km reflects a: a. low affinity of the enzyme for substrate b. same affinity of the enzyme for substrate c. high affinity of the enzyme for substrate d. low affinity of the enzyme for inhibitor The coenzyme is often: a. metal b. vitamin c. protein d. lipid 22. Apoenzyme & cofactor are collectively called: a. holoenzyme b. proenzyme c. isoenzyme d. coenzyme 23. Enzymes: a. do not require activation energy b. do not change activation energy c. lower activation energy d. increase activation energy 24. Competitive inhibitor: a. binds a site other than active site b. binds active site c. increase Vmax d. decrease Km 25. Non competitive inhibitor: a. is similar to the substrate b. binds active site c. increases Vmax d. does not change Km 26. Michaelis constant (Km) is: a. enzyme concentration at half Vmax b. substrate concentration at half Vmax c. inhibitor concentration at half Vmax d. substrate concentration at Vmax Concerning disorders due to vitamin deficiency or excess a. excess intake of vitamin B1 can cause severe toxic reactions b. B2 deficiency is not fatal & characterized by ocular disturbances c. vit B12 deficiency results in microcytic anemia d. rickets can be prevented by large doses of vit C Tryptophan is an amino acid which is a provitamin of a. niacin b. thiamine c. vitamin D d. vitamin K In adults, severe deficiency of vitamin D causes a. night blindness b. osteomalacia c. osteopetrosis d. osteopetrosis Night Blindness & Xerophthalmia are symptoms of deficiency of a. vitamin C b. vitamin K c. vitamin A d. vitamin E Biotin is a coenzyme of the enzyme a. carboxylase b. hydroxylase c. decarboxylase d. deaminase The precursor of CoA is: a. riboflavin b. Pyridoxamine c. thiamin d. pantothenate 37. About water-soluble vitamins a. they are stored in the body b. they are not excreted in the urine c. they are soluble in lipid d. they are generally non-toxic (no hypervitaminosis) 38. Transketolase activity is measured to detect deficiency of, a. riboflavin b. niacin c. thiamin d. ascorbic acid 39. Important coenzyme in decarboxylation of amino acids & transamination reactions: a. Vitamin E b. Vitamin A c. Pyridoxal-5-phosphate d. pantothenic acid 40. Niacin: a. is the precursor of FAD b. is the precursor of PLP c. its deficiency leads to pellagra d. its deficiency leads to beriberi