Question

56. In the lock and key model of substrate binding to enzymes Pprat wnich they work best a the substrate changes its conformation to fit the active site b. the active site changes its conformation to fit the substrate c. the active site is rigid and the substrate must fit exactly d. the substrate binds only to part of the active site In the induced-fit model of substrate binding a. 57. the substrate changes its conformation to fit the active site b. the active site stays the same, but the rest of the enzyme changes when substrate binds there is a conformation change in the enzyme active site when the substrate binds d. c. there is aggregation of several enzyme molecules when the substrate binds An important step in elucidating the behavior of an enzyme is a. 58. obtaining a crystalline sample of the enzyme b. insuring that metal ions are always excluded from the enzyme sample determining the active site residues c. d. none of the above An explanation for the mechanism of competitive inhibition of an enzyme is that a. both the substrate and the inhibitor fit into the active site b. only the inhibitor fits into the active site c. the substrate fits into the active site even though the inhibitor changes the shape of the 59. enzyme by attachment to another site d. only the substrate fits into the active site At very high substrate levels the maximum rate is achieved when 60. no inhibitor is present a. b. a competitive inhibitor is present c. a noncompetitive inhibitor is present d. either a or b When a noncompetitive inhibitor is present 61. sufficiently high substrate levels can still give maximal velocity a. it binds to a site other than the active site and slows down the catalysis b. the inhibitor and the natural substrate cannot bind at the same time c. d. none of the above The fundamental difference between competitive and noncompetitive inhibition is 62. the degree of cooperativity of the reaction the size of the active site of the enzyme the manner of binding of substrate to the enzyme the manner of binding inhibitor to the enzyme a. b. C. d.

Answer 1

Ans 56 : c) the active site is rigid and the substrate must fit exactly.

According to the lock and key model of enzyme action , the substrate acts as a specific key that has a shape complimentary to the shape of active site of the enzyme. This ensures the specificity of the enzyme molecule as only a particular kind of substrate can bind onto it and bring about the reaction.