18 Questions
Which of the following statements is true regarding the Michaelis constant?
A low value of the Michaelis constant indicates low affinity for a substrate.
Which type of enzyme is frequently composed of multiple subunits?
Allosteric enzymes
What is the effect of phosphorylation on HMG-CoA reductase?
It increases the enzyme's activity.
Which of the following is an example of a ligase?
None of the above
What is the effect of competitive inhibitors on the Michaelis constant?
They increase the Michaelis constant.
What is the characteristic of an enzyme with high affinity for its substrate?
It has a low value of the Michaelis constant.
What is the primary function of aminotransferases in cells?
To serve as an indicator of some diseases
What does the Michaelis constant characterize?
The substrate specificity of an enzyme
What is the role of enzymes in a reaction?
To decrease the energy barrier
What type of catalysis involves the covalent bonding of the substrate to the enzyme?
Covalent catalysis
What is the term for a molecule that binds to an enzyme and alters its activity?
Inhibitor
What is the term for multiple forms of an enzyme that have the same function but differ in their amino acid sequence?
Isozymes
What is the effect of a noncompetitive inhibitor on the Michaelis constant?
It increases the Michaelis constant
Which of the following statements is true about coenzyme A?
It is a carrier of acyl groups
What is the characteristic of an enzyme that exhibits a Km value of 10^(-3)M?
Low substrate affinity
What is the effect of an inhibitor on the kinetics of an enzymatic reaction, if Vmax is decreased and Km is unchanged?
Noncompetitive inhibition
What is a characteristic of isozymes?
All of the above
What is the effect of an enzyme on the standard Gibbs free energy change (ΔG0) of a reaction?
It has no effect on ΔG0
Study Notes
Enzyme Catalysis
- Enzymes catalyze the joining of two molecules.
- The Michaelis constant (Km) is a measure of the concentration of enzyme needed to achieve half of the maximal velocity of reaction.
Enzyme Inhibition
- Competitive inhibitors bind to the active site of the enzyme and do not change the Vmax of the reaction.
- Noncompetitive inhibitors do not bind to the active site and decrease the Vmax of the reaction.
Enzyme Structure
- Lactate dehydrogenase (LDH) is composed of 4 subunits.
- LDH isoenzymes catalyze different reactions in muscle and heart.
Isozymes
- Isozymes can have different Km for the same substrate.
- Isozymes can have different isoelectric points.
- LDH is coded by 4 genes and can form 5 isozymes.
Enzyme Kinetics
- Vmax is the maximum velocity of an enzymatic reaction.
- Km is the Michaelis constant, which is a measure of the enzyme's affinity for its substrate.
- The Michaelis constant can be affected by the presence of inhibitors.
Types of Enzymes
- Pepsin is a hydrolase.
- Amylase is a hydrolase.
- Aminotransferases are a type of transferase.
- Oxidoreductases, transferases, hydrolases, isomerases, and lyases are all classes of enzymes.
Allosteric Enzymes
- Allosteric enzymes frequently contain multiple subunits.
- Allosteric enzymes can be conformationally changed by allosteric effectors that alter Km or Vmax.
Enzyme Regulation
- Phosphorylation-dephosphorylation is associated with serine, threonine, or tyrosine residues of the enzyme.
- HMG-CoA reductase is active in its dephosphorylated form.
Clinical Enzymology
- LDH activity in plasma can serve as an indicator of some diseases.
- Aminotransferase activity in plasma can increase in pancreatic disease.
- LDH activity in plasma can increase in myocardial infarction.
Diagnosis
- Measure LDH activity to diagnose myocardial infarction.
- Measure aminotransferase activity to diagnose viral hepatitis.
- Measure prostate-specific antigen (PSA) activity to diagnose metastatic carcinoma of the prostate.
Test your knowledge of biochemistry with this quiz on enzymes, coenzymes, and their roles in biochemical reactions. Questions cover topics like Michaelis constant, coenzyme A, and riboflavin.
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