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Questions and Answers
Which of the following statements is true regarding the Michaelis constant?
Which of the following statements is true regarding the Michaelis constant?
- A low value of the Michaelis constant indicates low affinity for a substrate. (correct)
- Competitive inhibitors can decrease the value of the Michaelis constant.
- Noncompetitive inhibitors can increase the value of the Michaelis constant.
- A high value of the Michaelis constant indicates high affinity for a substrate.
Which type of enzyme is frequently composed of multiple subunits?
Which type of enzyme is frequently composed of multiple subunits?
- Hydrolases
- Oxidoreductase
- Allosteric enzymes (correct)
- Transferases
What is the effect of phosphorylation on HMG-CoA reductase?
What is the effect of phosphorylation on HMG-CoA reductase?
- It is associated with serine or threonine residues only.
- It increases the enzyme's activity. (correct)
- It decreases the enzyme's activity.
- It has no effect on the enzyme's activity.
Which of the following is an example of a ligase?
Which of the following is an example of a ligase?
What is the effect of competitive inhibitors on the Michaelis constant?
What is the effect of competitive inhibitors on the Michaelis constant?
What is the characteristic of an enzyme with high affinity for its substrate?
What is the characteristic of an enzyme with high affinity for its substrate?
What is the primary function of aminotransferases in cells?
What is the primary function of aminotransferases in cells?
What does the Michaelis constant characterize?
What does the Michaelis constant characterize?
What is the role of enzymes in a reaction?
What is the role of enzymes in a reaction?
What type of catalysis involves the covalent bonding of the substrate to the enzyme?
What type of catalysis involves the covalent bonding of the substrate to the enzyme?
What is the term for a molecule that binds to an enzyme and alters its activity?
What is the term for a molecule that binds to an enzyme and alters its activity?
What is the term for multiple forms of an enzyme that have the same function but differ in their amino acid sequence?
What is the term for multiple forms of an enzyme that have the same function but differ in their amino acid sequence?
What is the effect of a noncompetitive inhibitor on the Michaelis constant?
What is the effect of a noncompetitive inhibitor on the Michaelis constant?
Which of the following statements is true about coenzyme A?
Which of the following statements is true about coenzyme A?
What is the characteristic of an enzyme that exhibits a Km value of 10^(-3)M?
What is the characteristic of an enzyme that exhibits a Km value of 10^(-3)M?
What is the effect of an inhibitor on the kinetics of an enzymatic reaction, if Vmax is decreased and Km is unchanged?
What is the effect of an inhibitor on the kinetics of an enzymatic reaction, if Vmax is decreased and Km is unchanged?
What is a characteristic of isozymes?
What is a characteristic of isozymes?
What is the effect of an enzyme on the standard Gibbs free energy change (ΔG0) of a reaction?
What is the effect of an enzyme on the standard Gibbs free energy change (ΔG0) of a reaction?
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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.
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