Which of the following statements about the different types of enzyme inhibition

Question

Which of the following statements about the different types of enzyme inhibition is false? A. A competitive inhibitor decreases Vmax, but does not affect K». B. Competitive inhibition occurs when the substrate and the inhibitor compete for the active site of the enzyme C. Noncompetitive inhibition of an enzyme cannot be overcome by adding large amounts of substrate. D. Competitive inhibitors are often similar in chemical structure to the substrates of the inhibited enzyme E. An irreversible inhibitor forms a covalent bond with an enzyme Which of the following statements about the active site and catalytic mechanism of chymotrypsin is true? A. An acyl-enzyme intermediate is formed between the His residue of the catalytic triad and the carbonyl group resulting from the cleaved peptide bond B. Hydrogen bonds stabilize the oxyanion that is formed in the tetrahedral transition state in the reaction. C. The Asp residue of the catalytic triad orients the substrate properly for the reaction. D. The Asp residue of the catalytic triad initiates the deacylation step by a nucleophilic attack on the carbonyl carbon of the acyl intermediate E. The binding pocket contains an Asp residue which is involved in electrostatic interactions with the Lys or Arg residues. Which of the following statements about trypsin, elastase, and chymotrypsin is false? A. They have similarities in amino acid sequence and three dimensional structure B. They all catalyze reactions that proceed through a covalent intermediate C. They have evolved from a common ancestor, subtilisin. D. They have different substrate specificities. E. They are synthesized in the pancreas as inactive zymogens. Activation of serine proteinase zymogens involves A. glycosylation of Asn residues B. phosphorylation of Ser and Thr residues C. proteolytic cleavage D. allosteric interactions E. all of the above Which of the following statements is false? A. At a pH lower than a protein's isoelectric point, the protein has a net positive charge B. In SDS-polyacrylamide gel electrophoresis (SDS-PAGE), proteins are separated primarily on the basis of their size and not their charge C. SDS-PAGE denatures protein samples, whereas gel permeation chromatography does not. D. Mass spectrometry provides a more precise determination of protein mass than either SDS- polyacrylamide gel electrophoresis or gel permeation chromatography E. In both SDS-PAGE and gel permeation chromatography, small proteins migrate faster than large proteins.

Explanation / Answer

Ans-1 the false statement is (A) i.e. competitive inhibitor decrease Vmax but have no effect on Km.

because the competitive inhibitor increase the Km but have no effect on the Vmax.

ans-2 the correct option is (D) i.e. the Asp residue of catalytic triad initiates the deacylation step by nucleophile attack on the carbonal carbon of the acyl intermediate.

ans-3 the correct option is (A) i.e. they have similar amino acid sequence and three dimensional structure.

because there are diffrences in their amino acid sequences.

ans-4 the correct option is (E) i.e. all of above.

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