Enzymes Flashcards
Enzymes
Biological catalysts that do not impact the thermodynamics of a biological rxn but increase the rate at which it occurs
- Lowers the activation energy
- Does not change free energy (G) or enthalpy (H)
- Does not alter equilibrium
- Changes rate of rxn (kinetics)
Lock and Key Model
Enzyme active site (lock) is already in the appropriate conformation for the substrate (key) to bind
Induced Fit Model
Shape of the active site becomes truly complementary only after the substrate begins binding. These enzymes return to their original shape after the substrate leaves
Cofactors
Inorganic molecules and metal ions
- Small so that they can bind to the active site of an enzyme to aid in conformation change. Participate in catalysis by carrying charge through the ionization, polarization or depolarization
CoEnzymes
Organic molecules
- Small so that they can bind to the active site of an enzyme to aid in conformation change. Participate in catalysis by carrying charge through the ionization, polarization or depolarization
Saturation
All enzyme active sites are occupied by the substrate
As [substrate] increases, the reaction rate also increases until Vmax is reached
Vmax
Maximum velocity of reaction; only increased by increasing the [Enzyme]
Michaelis-Menten
E+S ES —-> E+P
Vmax [S]
________ = V
Km + [S]
Km
Measure of the affinity of an enzyme for its substrate
Increased Km means decreased affinity because
Km = 1/2 Vmax = [S]
Competitive Inhibition
Binds to E at the Active Site
Increases Km
Vmax remains unchanged
**Overcome by adding excess Substrate
NonCompetitive Inhibition
Binds to E and ES at an Allosteric Site
Km Remains unchanged
Vmax Decreases
Uncompetitive Inhibition
Binds to ES at an Allosteric Site
Km decreases
Vmax Decreases
Mixed Inhibition
Binds to E and ES at Allosteric Site
Km can increase or decrease
Vmax Decreases
Feedback Regulation
Regulation by products created further down in the pathway
Feed Forward Regulation
Intermediates preceding the enzyme are the regulators
Negative Feedback Regulation
Product binds to the active site of an enzyme earlier in the pathway inhibiting them or making them unavailable
Allosteric Enzymes
Contain multiple binding sites
Covalently Modified Enzymes
Transient - allosteric activation / inhibition
Covalent - glycoslation / phosphorylation
Zymogens
Inactive Enzyme; contain a regulatory domain which must be removed or altered to expose the active site
Ligases
Responsible for joining two large biomolecules (often of the same type)
Isomerases
Catalyze the interconversion of isomers, including both constitutional and stereoisomers
Lyases
Catalyze cleavage without the addition of water and without the transfer of electrons
*Reverse rxn = synthesis
Hydrolases
Catalyze cleavage with the addition of water
Oxidoreductases
Catalyze oxidation - reduction reactions that involve the transfer of electrons
Transferases
Move a functional group from one molecule to another molecule
