Question

The figure given below shows three velocity-substrate concentration curves for an enzyme reaction. What does the curve a, b, and c depict respectively

• A. a = Enzyme with an allosteric modulator added,
  b = Normal enzyme activity
  c = competitive inhibition
• B. a = Normal enzyme reaction
  b = Competitive inhibition
  c = Non-competitive inhibition
• C. a=Enzyme with an allosteric stimulator
  b = competitive inhibition added
  c = normal enzyme reaction
• D. a = Normal enzyme reaction
  b = Non-competitive inhibitor added
  c = Allosteric inhibitor added.

Answer 1

The correct option is B a = Normal enzyme reaction

b = Competitive inhibition
c = Non-competitive inhibition
The above curves show normal enzyme reaction, competitive and non-competitive inhibitions. This graph shows the rate of reaction (v) plotted against substrate concentration ([S]) for an enzyme-catalyzed reaction (green line), the identical reaction in the presence of a competitive inhibitor (blue line), and the identical reaction in the presence of a noncompetitive inhibitor (orange line). In the presence of the competitive inhibitor, the maximal rate of the reaction (Vmax) is unchanged; however, the Michaelis constant (Km), which is the substrate concentration at 1/2 Vmax, is increased. This is indicative of the lower affinity of the enzyme for the substrates in the presence of a competitive inhibitor that binds to the active site. In the presence of a noncompetitive inhibitor, the maximal rate of the reaction (Vmax) is lower but the Michaelis constant (Km) is unchanged. This is indicative of the reduced activity of the enzyme in the presence of the noncompetitive inhibitor, which does not bind to the active site and therefore does not alter substrate binding.