Enzymes Flashcards
(24 cards)
What are isozymes?
Enzymes that catalyze the same reaction but are encoded by different genes and may have different kinetic properties or regulatory mechanisms
Isozymes allow for regulation and adaptation in different tissues or conditions.
What are allozymes?
Variants of the same enzyme encoded by the same gene, differing due to genetic polymorphisms (allelic variations)
Allozymes can be used to study genetic diversity within populations.
How do enzymes catalyze metabolic reactions?
By lowering activation energy, increasing reaction rates without altering thermodynamics
Enzymes facilitate reactions without being consumed in the process.
What types of modifications regulate enzyme activity?
Both covalent and noncovalent modifications
These modifications can include phosphorylation, methylation, and allosteric regulation.
What are inhibitors and activators?
Substances that affect enzyme activity, including synthetic compounds (drugs), exogenous compounds (toxins), and endogenous compounds (allosteric effectors)
They play crucial roles in metabolic regulation and drug design.
What does thermodynamics determine in a reaction?
The reaction’s feasibility and extent
It tells us if a reaction can occur based on energy differences.
What does kinetics govern in a reaction?
The speed of the reaction by influencing activation energy
Kinetics provides insight into how quickly reactants are converted to products.
In an endergonic reaction, what can be said about the concentrations of A and B?
[A] > [B]
Endergonic reactions require energy input and do not occur spontaneously.
In an exergonic reaction, what can be said about the concentrations of A and B?
[A] < [B]
Exergonic reactions release energy and occur spontaneously.
What are coupled reactions?
Reactions that drive energetically unfavorable processes by linking them to spontaneous reactions
This mechanism is essential for many biochemical pathways.
What is a toxic intermediate produced by peroxisomes?
Hydrogen peroxide (H₂O₂)
Peroxisomes detoxify substances, converting H₂O₂ into water to prevent toxicity.
Name one advantage of coupled reactions.
Regulation of metabolic pathways
Coupling allows cells to control reaction rates based on energy availability.
What is the role of the sodium-potassium (Na⁺/K⁺) pump?
Maintains resting membrane potential in nerve and muscle cells
It uses ATP hydrolysis to move ions against their gradients.
What factors affect the rate of an enzyme-catalyzed reaction?
- Enzyme concentration
- Catalytic turnover
- Substrate concentration
- Substrate-enzyme affinity
These factors are crucial for optimizing enzyme activity in metabolic pathways.
What is catalytic turnover?
The number of substrate molecules an enzyme converts into product per unit time when the enzyme is fully saturated with substrate
It reflects the efficiency of the enzyme.
What is the Michaelis constant (Km)?
The substrate concentration where the enzyme works at half Vmax
A lower Km indicates a higher affinity of the enzyme for the substrate.
What happens in competitive inhibition?
The inhibitor mimics substrate and binds to the active site, increasing Km but leaving Vmax unchanged
This type of inhibition can be overcome by increasing substrate concentration.
What happens in non-competitive inhibition?
The inhibitor binds to another site, changing enzyme shape, decreasing Vmax but leaving Km the same
This type of inhibition cannot be overcome by increasing substrate concentration.
What is irreversible inhibition?
The inhibitor permanently binds to the enzyme, completely inactivating it
Examples include nerve gas and penicillin.
What is uncompetitive inhibition?
The inhibitor binds only to the enzyme-substrate complex, preventing product release, decreasing both Km and Vmax
This type of inhibition reduces the overall efficiency of the enzyme.
What characterizes allosteric enzymes?
They show a sigmoidal (S-shaped) curve instead of a hyperbolic one, indicating cooperative binding
Binding one substrate makes it easier for the enzyme to bind more substrates.
What is the T-state of allosteric enzymes?
The state with low affinity for substrate
This state is contrasted with the R-state, which has high affinity.
What is a negative feedback loop in metabolic pathways?
The final product of a pathway inhibits an earlier enzyme, preventing wasteful overproduction
Example: ATP inhibits enzymes in glycolysis.
What occurs at steady-state in enzyme kinetics?
The rate of enzyme-substrate formation equals the rate of breakdown
This is a foundational concept in the Michaelis-Menten equation.
