ainfoera.com – MCQs, Mock Tests | Biochemistry Biochemistry MCQS PAPER SET 11

1 ï»¿The molecular formula for glycine is C2H5O2N. What would be the molecular formula for a linear oligomer made by linking ten glycine molecules together by condensation synthesis?

A C20H50O20N10 B C20H32O11N10 C C20H40O10N10 D C20H68O29N10

✅ Correct Answer: 2

2 Which of the following is an example of tertiary structure in a protein?

A A multimeric protein B An a-helix C A P-pleated sheet D A globular domain

✅ Correct Answer: 4

3 The peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala, was digested with cyanogen bromide (CNBr) to produce:

A Val-Lys + Glu-Met-Ser + Trp-Arg-Ala B Val-Lys-Glu-Met-Ser-Trp + Arg-Ala C Val-Lys-Glu-Met + Ser-Trp-Arg-Ala D Val-Lys-Glu + Met-Ser-Trp-Arg-Ala

✅ Correct Answer: 3

4 In deoxy hemoglobin (Hb), the Fe (II) is coordinated to

A four nitrogens of heme, the proximal His, and a water molecule B four nitrogens of heme and to a water molecule C two nitrogens of heme and to three His residues in Hb D two nitrogens of heme and to three water molecules

✅ Correct Answer: 1

5 In the Î²-pleated sheet

A hydrogen bonds are formed between the peptide bonds B adjacent polypeptide chains can either be parallel or antiparallel C the polypeptide chain is fully extended D all of the above

✅ Correct Answer: 4

6 The Ramachandran Plot illustrates the fact that

A the peptide bond is planar B the F & Y angles can assume any value in a peptide C the F & Y angles can assume only a single value in a protein D the F & Y angles can assume approximately three different values

✅ Correct Answer: 4

7 The resonance structures that can be drawn for the peptide bond indicate that the peptide bond

A is stronger than an ordinary single bond B has partial double bond character C both (a) and (b) D is still not completely understood

✅ Correct Answer: 3

8 The major element of secondary structure in myoglobin and hemoglobin is

A the P-strand B the a-helix C the reverse turn D All of these

✅ Correct Answer: 2

9 An oil drop with a polar coat is a metaphor referring to the three dimensional structure of

A fibrous proteins B collagen C globular proteins D silk protein

✅ Correct Answer: 3

10 What was the first protein whose complete tertiary structure was determined?

A Lysozyme B Myoglobin C Pancreatic ribonuclease D Pancreatic Dnase

✅ Correct Answer: 2

11 The peptide bond in proteins is

A planar, but rotates to three preferred dihedral angles B nonpolar, but rotates to three preferred dihedral angles C nonpolar, and fixed in a trans conformation D planar, and usually found in a trans conformation

✅ Correct Answer: 4

12 In Î²-pleated sheet structures neighbouring

A chains lie in a flat plane B neighboring residues are hydrogen bonded C neighboring chains are connected by a-helices D neighboring chains are hydrogen bonded

✅ Correct Answer: 4

13 The same peptide, Val-Lys-Glu-Met-Ser-Trp-Arg-Ala. was digested with chymotrypsin to produce

A Val-Lys + Glu-Met-Ser + Trp-Arg-Ala. B Val-Lys-Glu-Met-Ser-Trp + Arg-Ala. C Val-Lys-Glu-Met-Ser + Trp-Arg-Ala. D Val-Lys-Glu-Met + Ser-Trp-Arg-Ala.

✅ Correct Answer: 2

14 Disulfide bonds most often stabilize the native structure of

A extracellular proteins B dimeric proteins C hydrophobic proteins D intracellular proteins

✅ Correct Answer: 1

15 Secondary structure in protein refers to

A linear sequence of amino acids joined together by peptide bond B three dimensional arrangement of all amino acids in polypeptide chain C regular folding of regions of the polypeptide chain D protein made up of more than one polypeptide chain

✅ Correct Answer: 3

16 Heme is the binding pocket of myoglobin and hemoglobin and is composed of

A negatively charged residues B polar residues C hydrophobic residues D positively charged residues

✅ Correct Answer: 3

17 What is the effect of a decrease in pH on hemoglobin oxygen affinity?

A Decrease in oxygen affinity B Increase in oxygen affinity C No effect on oxygen affinity D Increase affinity in muscle cell otherwise decrease

✅ Correct Answer: 1

18 What is the proportion of glycine residues in collagenous regions?

A One-fourth B One-third C Half D One-tenth

✅ Correct Answer: 2

19 Which of the following statements is incorrect?

A Protein G contains both a-helix and P-sheet B Protein G contains only a-helix C Fatty acid binding protein contains largely P-sheet D Hemoglobin contains four sub-units

✅ Correct Answer: 2

20 The oxygen binding curves of hemoglobin and myoglobin

A allow maximum transfer of oxygen to the tissues B are a consequence of the quaternary structure of hemoglobin C Hydrogen bond D are identical

✅ Correct Answer: 3

21 The nature of peptide bond can be best explained as

A partial double bond B truly double bond C Hydrogen bond D Van der waals force

✅ Correct Answer: 1

22 Which of the following statement is incorrect?

A Hemoglobin and myoglobin are the two oxygen binding proteins B Hemoglobin transports O2 in the blood C Myoglobin stores O2 in muscles D None of the above

✅ Correct Answer: 4

23 Which hemoglobin chain replaces the beta chain in embryonic hemoglobulin?

A Delta B Epsilon C Gamma D Alfa

✅ Correct Answer: 2

24 Hemoglobin has quaternary structure and is made up of

A six polypeptide chains, two Î±-chains and four Î²-chains B two polypeptide chains, one Î±-chains and one Î²-chains C four polypeptide chains, two Î±-chains and two Î²-chains D five polypeptide chains, two Î±-chains and three Î²-chains

✅ Correct Answer: 3

25 Peptides in the fully extended chain conformation

A have Y = F = 180Â° B do not occur in nature C also have a cis geometry in their peptide bonds D are equivalent to the (3-sheet structure

✅ Correct Answer: 1

26 The oxygen in hemoglobin and myoglobin is bound to

A the iron atom in the heme group B the nitrogen atoms on the heme C histidine residues in the protein D lysine residues in the protein

✅ Correct Answer: 1

27 Which of the three subunits of the G proteins binds GDP and GTP?

A Alpha B Beta C Gamma D Delta

✅ Correct Answer: 1

28 If the F and Y angles of each peptide unit in a protein are known, which of the following may also be determined?

A Complete secondary structure B Complete tertiary structure C Complete quaternary structure D Thermodynamic stability

✅ Correct Answer: 1

29 The different orders of protein structure are determined by all of the following bond types except

A peptide bonds B phospho-diester bonds C disulfide bridges D hydrogen bonds

✅ Correct Answer: 2

30 The heme is held in place by a bond between

A the Fe2+ and cysteine B the Fe3+ and histidine C the Fe3+ and cysteine D the Fe2+ and histidine

✅ Correct Answer: 4

31 Unpaired H-bond donors and acceptors are found in the hydrophobic core of a protein

A only at the ends of a-helices B only at the turns connecting p-strands C only on Pro residues D rarely

✅ Correct Answer: 4

32 For the unfolding reaction of Protein G, Î”HÂ° =210.6 kJ/mol, this means that

A unfolding is favored enthalpically B folding is favored enthalpically C the entropy is positive at all temperatures D the entropy is negative at all temperatures

✅ Correct Answer: 2

33 Attractive Vander Waals forces occur between

A apolar molecules in the liquid state B any pair of nearby atoms C polar molecules in the solid state D only if other forces are less favorable

✅ Correct Answer: 2

34 Which of the following forces is the most favorable for protein folding?

A Conformational entropy B Hydrophobic Interactions C Vander Waals interactions D Hydrogen bonds

✅ Correct Answer: 2

35 At the midpoint of a temperature transition curve,

A half of the protein is denatured B Keq = 1.0 and Î”G = 0 C [Native] = [Unfolded] D All of these

✅ Correct Answer: 4

36 Which of the following is the most correct?

A Charged amino acids are never buried in the interior of a protein B Charged amino acids are seldom buried in the interior of a protein C All hydrophobic amino acids are buried when a protein folds D Tyrosine is only found in the interior of proteins

✅ Correct Answer: 2

37 Which of the following forces is the most unfavorable for protein folding?

A Conformational entropy B Hydrophobic interactions C Vander Waals interactions D Electrostatic interactions

✅ Correct Answer: 1

38 Since Î”GÂ° = -RTlnK

A a 10-fold increase in K decreases Î”GÂ° by about 10-fold B a 10-fold decrease in K decreases Î”GÂ° by about 2.3*RT C a 10-fold increase in K decreases Î”GÂ° by about 2.3*RT D a 10-fold decrease in K increases Î”GÂ° by about 10-fold

✅ Correct Answer: 3

39 The correlation between free energy Î”G transfer between the aqueous/organic phases and the surface area of amino acid residues

A reflects the reduction in solvent-accessible area during protein folding B is only meaningful for the polar amino acids C ignores the important contribution of the peptide bond D is similar to effects seen with SDS denaturation

✅ Correct Answer: 1

40 If the egg white protein, ovalbumin, is denatured in a hard-boiled egg, then which of the following is least affected?

A The primary structure of ovalbumin B The secondary structure of ovalbumin C The tertiary structure of ovalbumin D The quaternary structure of ovalbumin

✅ Correct Answer: 1

41 Buried hydrophobic side chains in a globular protein fit into a hole formed by the side chains of

A 1-3 other amino acids B 5-7 other amino acids C 9-12 other amino acids D 13-15 other amino acids

✅ Correct Answer: 2

42 In an SDS-PAGE

A proteins are denatured by the SDS B proteins have the same charge-to-mass ratio C smaller proteins migrate more rapidly through the gel D all of the above

✅ Correct Answer: 4

43 Proteins can be visualized directly in gels by

A staining them with the dye B using electron microscope only C measuring their molecular weight D none of these

✅ Correct Answer: 1

44 In SDS-PAGE, the protein sample is first

A treated with a reducing agent and then with anionic detergent followed by fractionation by electrophoresis B fractionated by electrophoresis then treated with an oxidizing agent followed by anionic detergent. C treated with a oxidizing agent and then with anionic detergent followed by fractionation by electrophoresis D none of the above

✅ Correct Answer: 1

45 Electrophoresis of histones and myoglobin under non-denaturing conditions (pH = 7.0) results in

A both proteins migrate to the anode B histones migrate to the anode and myoglobin migrates to the cathode C histones migrate to the cathode and myoglobin migrates to the anode D both proteins migrate to the cathode

✅ Correct Answer: 3

46 In isoelectric focusing, proteins are separated on the basis of their

A relative content of positively charged residue only B relative content of negatively charged residue only C size D relative content of positively and negatively charged residue

✅ Correct Answer: 4

47 In a gel filtration column

A smaller proteins enter the beads more readily B large proteins elute first C both (a) and (b) D large proteins enter the beads more readily

✅ Correct Answer: 3

48 In a native PAGE, proteins are separated on the basis of

A net negative charge B net charge and size C net positive charges size D net positive charge

✅ Correct Answer: 2

49 The subunit molecular weight as well as the number of subunits in the quaternary structure can be determined by

A SDS-PAGE electrophoresis B gel filtration chromatography C combining information from (a)and (b) D isoelectric focusing

✅ Correct Answer: 3

50 Proteins are separated in an SDS-PAGE experiment on the basis of their

A positively charged side chains B molecular weight C negatively charged side chains D different isoelectric points

✅ Correct Answer: 2

51 Enzyme-driven metabolic pathways can be made more efficient by

A concentrating enzymes within specific cellular compartments B grouping enzymes into free-floating, multienzyme complexes C fixing enzymes into membranes so that they are adjacent to each other D All of the above

✅ Correct Answer: 4

52 Which of the following (s) is/are serine proteases?

A Chymotrypsin B Trypsin C Elastase D all of these

✅ Correct Answer: 4

53 Which of the following statements about enzymes or their function is true?

A Enzymes do not alter the overall change in free energy for a reaction B Enzymes are proteins whose three-dimensional form is key to their function C Enzymes speed up reactions by lowering activation energy D All of the above

✅ Correct Answer: 4

54 Tryprotophan synthetase of E.coli, a typical bifunctional oligomeric enzyme consist of

A a protein designated A B two proteins designated A and B C a protein A and one-subunit a D a protein designated B

✅ Correct Answer: 2

55 What is the specificity of the Clostripain protease?

A It cleave after Arg residues B It cleave after His residues C It cleave after Lys residues D None of the above

✅ Correct Answer: 1

56 The proteolysis rate enhancement by chymotrypsin (~1010 folds) corresponds to a reduction in activation energy of about

A 40 kJ/mol B 49 kJ/mol C 58 kJ/mol D 88 kJ/mol

✅ Correct Answer: 3

57 Which of the following is false statement with regard to comparison between Serine and HIV proteases?

A Both use nucleophilic attack to hydrolyze the peptide bond B Both require water to complete the catalytic cycle C Both forms an acyl-enzyme intermediate D Both show specificity for certain amino acid sequences

✅ Correct Answer: 3

58 In the enzyme-catalyzed reaction shown below, what will be the effect on substances A, B, C, and D of inactivating the enzyme labeled E2? A ---(E1)---> B ---(E2)---> C ---(E3)--->

A A, B, C, and D will all still be produced B A, B, and C will still be produced, but not D C A and B will still be produced, but not C or D D A will still be produced, but not B, C, or D

✅ Correct Answer: 3

59 The nucleophile in serine proteases is

A Serine B water C both (a) and (b) D Asparagine

✅ Correct Answer: 3

60 The role of Asp 102 and His 57 during trypsin catalysis is to

A neutralize the charge on the other's side chain B keep the specificity pocket open C function as a proton shuttle D clamp the substrate into the active site

✅ Correct Answer: 3

61 The cleavage specificity of trypsin and chymotrypsin depend in part on the

A proximity of Ser 195 to the active site or specificity pocket B size, shape, and charge of the active site or specificity pocket C presence of a low-barrier hydrogen bond in the active site or specificity pocket D absence of water in the active site

✅ Correct Answer: 2

62 The E.coli pyruvic acid dehydrogenase complex is reported to

A decatalyze the oxidation of pyruvic acid to acetyl Co A and CO2 B Catalyze the oxidation of pyruvic acid to acetyl Co A and CO2 C retard the reduction of pyruvic acid to acetyl Co A and CO2 D Catalyze the reduction of pyruvic acid to acetyl Co A and CO

✅ Correct Answer: 2

63 Which of the common features are shared between serine and aspartate proteases?

A Both require water to complete the catalytic cycle B Both use a base to activate the nucleophile C Both show specificity for certain amino acid sequences D All of the above

✅ Correct Answer: 4

64 Before they can react, many molecules need to be destabilized. This state is typically achieved through

A changing the three-dimensional shape of the molecule B oxidizing the molecules by removing electrons C changing the reaction from a biosynthetic to a catabolic pathway D the input of a small amount of activation energy

✅ Correct Answer: 4

65 Common feature in all serine proteases is a

A hydrophobic specificity pocket B hydrophilic specificity pocket C cluster of reactive serine residues D single reactive serine residue

✅ Correct Answer: 4

66 How is the enzyme COX-1 important in human health?

A It helps to transport carbon dioxide in the blood B It is critical for the biosynthesis of DNA C It is a chemical derivative of aspirin D It catalyzes the production of hormones that maintain the stomach lining

✅ Correct Answer: 4

67 For specific antigen recognition by T cells,

A antigen is bound by a T cell membrane antibody B denaturation of antigen does not reduce epitope recognition C MHC molecules are not required D antigen exposure during T cell maturation is required

✅ Correct Answer: 2

68 Antigen, when injected in the body activates its specific lymphocytes in the

A blood circulation B draining lymph nodes C MALT (mucosa associated D spleen lymphoid tissue

✅ Correct Answer: 2

69 A molecule that can be covalently linked to a non-immunogenic antigen to make it an immunogen is called a (n)

A adjuvant B carrier C hapten D mitogen

✅ Correct Answer: 2

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Biochemistry MCQS PAPER SET 11