Enzymes

Q1: 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

ANS:D - All of the above

No answer description is available.

Q2: 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

ANS:C - function as a proton shuttle

Asp 102 and His 57, how do they function as proton shuttles?

Q3: 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

ANS:A - proximity of Ser 195 to the active site or specificity pocket

The answer is correct becouse specificity of enzyme primerly depend on size, shape and charge of acrive site.

Q4: 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 CO2

ANS:B - Catalyze the oxidation of pyruvic acid to acetyl Co A and CO2

No answer description is available.

Q5: 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

ANS:D - All of the above

The enzymes are highly specific interacting with one or a few substrate and catalyzing only one type of chemical reaction.

Q6: 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

ANS:D - It catalyzes the production of hormones that maintain the stomach lining

Why not A? Explain please.

Q7: The nucleophile in serine proteases is

A Serine

B water

C both (a) and (b)

D Asparagine

ANS:C - both (a) and (b)

No answer description is available.

Q8: 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

ANS:D - single reactive serine residue

No answer description is available.

Q9: Which of the following (s) is/are serine proteases?

A Chymotrypsin

B Trypsin

C Elastase

D all of these

ANS:D - all of these

Serine proteasesare enzymes that cleave peptide bonds in proteins, in which serine serves as the nucleophilic amino acid at the (enzyme's) active site. They are found ubiquitously in both eukaryotes and prokaryotes.

Q10: 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

ANS:C - Both forms an acyl-enzyme intermediate

Because serine form tetrahedral intermediate and acyl-enzyme intermediate while HIV form just acyl-enzyme intermediate.

Q11: 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

ANS:D - All of the above

According to me, it is C. Because the enzymes work by providing an alternative pathway which requires less activation energy and not B. Because the three-dimensional structure that matters here is that of the active site but not the whole enzyme.

Q12: 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

ANS:C - 58 kJ/mol

Is it the Arrhenius equation that is used to solve the problem.

Q13: 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

ANS:D - the input of a small amount of activation energy

No answer description is available.

Q14: 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

ANS:C - A and B will still be produced, but not C or D

C and D will still be produced but at a slower rate than A and B.

Q15: 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

ANS:B - two proteins designated A and B

No answer description is available.

Q16: 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

ANS:A - It cleave after Arg residues

Please explain the answer.



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