Enzyme Kinetics and Regulation - Practice Flashcards (ENGLISH)/

Flashcards covering enzyme kinetics basics, Michaelis–Menten kinetics, inhibition types, allosteric regulation, covalent modifications, zymogens, isozymes, and clinical examples from the lecture notes.

What is an enzyme?

A protein that speeds up the rate of a chemical reaction (catalysis), is specific to a substrate, and is not consumed in the reaction.

What does enzyme kinetics deal with?

Rates of reactions and the factors that affect those rates.

What is Gibbs free energy?

The energy associated with a chemical reaction that can be used to do work.

What does Gibbs free energy change (ΔG) quantify?

The direction of a chemical reaction and the concentrations of reactants and products at equilibrium (ΔG = Gproducts − Greactants).

What does ΔG < 0 signify?

The process is exergonic and proceeds spontaneously in the forward direction to form more products.

What does ΔG > 0 signify?

The process is endergonic and tends to proceed in the reverse direction, forming more starting materials.

What does ΔG = 0 signify?

The system is at equilibrium and product/reactant concentrations remain constant.

What is activation energy?

The minimum energy required to change reactants into products.

How does temperature affect reaction rate?

Higher temperature increases kinetic energy and collisions (raising rate), but excess heat can denature enzymes and reduce activity.

What is the optimal pH range for enzyme activity?

Approximately pH 5–9.

What is the effect of substrate concentration on reaction rate?

Higher [S] leads to more productive collisions and a higher rate until saturation.

What does enzyme saturation mean in kinetics?

At high substrate concentration, all enzyme active sites are occupied, and the rate becomes limited by enzyme concentration (Vmax).

What do Vmax and Km represent?

Vmax is the maximum rate at a given enzyme concentration; Km is the substrate concentration at ½ Vmax and reflects enzyme–substrate affinity.

What does a low Km indicate about enzyme affinity?

Higher affinity for the substrate.

What is kcat?

The catalytic constant or turnover number: the number of substrate molecules converted to product per enzyme per second at Vmax.

What is the typical range for turnover number (kcat)?

About 10^2–10^4 s^-1.

What is the Michaelis–Menten equation best known for?

A simple model of enzyme kinetics describing how reaction rate depends on substrate concentration.

What is the significance of Km in enzymology?

It indicates the substrate concentration at half-maximal velocity and provides a measure of enzyme affinity for substrate.

What does a lower Km imply for enzyme affinity?

Higher affinity for its substrate.

What does kcat/Km describe?

Catalytic efficiency of an enzyme, especially at low substrate concentrations.

What is Lineweaver–Burk plot used for?

A linear representation of the Michaelis–Menten equation used to determine Km and Vmax.

What are reversible enzyme inhibitors?

Competitive, noncompetitive, and uncompetitive inhibitors.

What are irreversible inhibitors?

Inhibitors that covalently bind to the enzyme’s active site and permanently inactivate the enzyme (affinity reagents, suicide inhibitors, transition state analogs).

How do competitive inhibitors affect Km and Vmax?

Increase apparent Km (lower affinity at given [S]); Vmax remains unchanged.

How do noncompetitive inhibitors affect Km and Vmax?

Decrease Vmax; Km is unaffected.

How do uncompetitive inhibitors affect Km and Vmax?

Decrease both Vmax and Km.

What is an irreversible inhibitor?

Binds covalently to the active site, permanently inactivating the enzyme.

What are affinity reagents?

Substrate analogs with a reactive group that covalently blocks the active site.

What are suicide inhibitors?

Substrate analogs that are transformed by the enzyme into a reactive product that covalently binds and inactivates the enzyme.

What are transition state analogs?

Substrate analogs that resemble the transition state and bind tightly to the active site, often irreversibly inactivating the enzyme.

What is a toxin example of an irreversible enzyme inhibitor and its effect?

Sarin inhibits acetylcholinesterase, causing cholinergic toxicity and potentially fatal respiratory failure.

What is 5-fluorouracil (5-FU) and its target?

A thymidylate synthase inhibitor used in cancer therapy; blocks synthesis of thymidine for DNA replication.

How does penicillin inhibit bacteria?

Inhibits cell wall synthesis by covalently reacting with a serine in transpeptidase.

What is allosteric regulation?

Regulation where a regulatory molecule binds at a site other than the active site to modulate activity.

What is an effector in allosteric regulation?

A molecule that binds to an allosteric enzyme and modulates its activity.

What is the difference between homotropic and heterotropic effectors?

Homotropic: substrate itself acts as effector; heterotropic: different molecule acts as effector.

What is feedback inhibition?

End product of a pathway inhibits an earlier enzyme to regulate production (e.g., CTP inhibiting ATC in pyrimidine synthesis).

What is allosteric enzyme?

An enzyme with regulatory and substrate binding sites, often showing cooperativity and regulated by effectors.

What is the role of transcription factors in enzyme regulation?

Hormones and signals can regulate the synthesis of enzymes at the gene level.

What is ubiquitin–proteasome pathway?

Degrades defective or unnecessary proteins; regulation of protein turnover in cells.

What is enzyme compartmentalization?

Spatial separation of metabolic pathways in specific cellular locations (e.g., lysosomes, cytosol, mitochondria).

What is a zymogen?

An inactive precursor of an enzyme that is activated by proteolytic cleavage (e.g., pepsinogen to pepsin).