Enzymes

Topics in this chapter

• Enzyme Structure and Classification
• Enzyme Kinetics and Catalytic Efficiency
• Enzyme Inhibition Models
• Allosteric Regulation and Cooperativity
• Coenzymes and Vitamin-Derived Factors
• Zymogen Activation and Serine Proteases
• Enzymes in Toxicology and Metabolism

Practice questions

1. Question 1Q-694F2D

   A 45-year-old chronic alcoholic presents with peripheral neuropathy and severe memory impairment. Laboratory evaluation reveals a deficiency of thiamine, leading to impaired functioning of the pyruvate dehydrogenase complex. Which of the following coenzymes is NOT required by this multi-enzyme complex?

   1. A.Thiamine pyrophosphate (TPP)
   2. B.Pyridoxal phosphate (PLP)
   3. C.FAD (Flavin adenine dinucleotide)
   4. D.NAD+ (Nicotinamide adenine dinucleotide)
   See the answer and solution
2. Question 2Q-00FA47

   An enzyme-catalyzed reaction follows standard Michaelis-Menten kinetics. If the substrate concentration is equal to 3 times the Michaelis constant ($[S] = 3K_m$), what is the velocity of the reaction ($v$) expressed as a fraction of the maximum velocity ($V_{max}$)?

   1. A.0.25 Vmax
   2. B.0.50 Vmax
   3. C.0.75 Vmax
   4. D.0.90 Vmax
   See the answer and solution
3. Question 3Q-F795A1

   A patient is treated with a specific pharmacological inhibitor that binds reversibly to the active site of a target enzyme, preventing substrate binding. On a Lineweaver-Burk plot, how do the kinetic parameters $V_{max}$ and apparent $K_m$ change in the presence of this inhibitor?

   1. A.Vmax decreases, apparent Km remains unchanged
   2. B.Vmax remains unchanged, apparent Km increases
   3. C.Both Vmax and apparent Km decrease
   4. D.Vmax remains unchanged, apparent Km decreases
   See the answer and solution
4. Question 4Q-6108E5

   Which of the following classes of enzymes according to the International Union of Biochemistry and Molecular Biology (IUBMB) is responsible for catalyzing the joining of two molecules coupled with the hydrolysis of a nucleotide triphosphate?

   1. A.Transferases
   2. B.Hydrolases
   3. C.Lyases
   4. D.Ligases
   See the answer and solution
5. Question 5Q-90150D

   Allosteric enzymes characteristically show sigmoidal kinetics rather than hyperbolic kinetics on a velocity versus substrate concentration plot. This behavior is primarily a result of which of the following phenomena?

   1. A.Irreversible covalent modification of the catalytic subunit
   2. B.Cooperative binding of substrate molecules among multiple subunits
   3. C.Competitive inhibition by downstream metabolic end-products
   4. D.Total absence of a quaternary protein structure
   See the answer and solution