2.09 Enzymes Flashcards
specialized protein catalysts that accelerate chemical reactions, used in biochemical reactions and pathways
Enzymes
Mechanism of enzymes wherein there is conformational change when the substrate binds to the enzyme’s active site
Induced fit (Daniel Koshland)
The molecule acted upon by the enzyme to form a product
Substrate
Enzymes that require a metal in their composition
Metalloenzymes
Parts of a holoenzyme
Protein part
Cofactor (Non-protein part)
Examples of Cofactors
Coenzymes
Prosthetic groups
Metal Ions
Classes of Coenzymes
Activation Transfer Coenzymes
Oxidation Reduction Coenzymes
What to look for in enzyme cofactors
Coenzyme
Enzyme
Chemical groups transferred
Vitamin Precursor
The enzyme that catalyzes the rate-limiting or committed step of a metabolic pathway
Regulatory enzyme
Intracellular locations of some important biochemical pathways
Mitochondria
Cytosol
Nucleus
Lysosome
Different structural forms of an enzyme which catalyze the same chemical reactions
Isoenzyme
Enzymes that act on the same substrate and produce the same products but exhibit differing degrees of efficiency
Isoenzyme
Six major classes of enzymes
Oxidoreductases Transferases Hydrolases Lyases Lysases Isomerases Ligases
Part of the enzyme which contains amino acid side chains that participate in substrate binding and catalysis
Active site
Enzyme that transfer of electron and hydrogen atoms from donors
Oxidoreductases
Enzyme that transfers functional groups from donors to acceptors
Transferases
Enzyme that csatalyze cleavage of chemical bonds by addition of H2O, producing 2 products
Hydrolases
Enzyme that cleaves C-C, C-O, and C-N bonds by means other than hydrolysis or oxidation
Lyases
Enzyme that catalyzes a psychologically important reaction that favors the formation of a C-C bond
Synthase
Type of lyases that adds H2O to a substrate
Hydratase
Transfer of functional groups or double bonds within the same molecule
Isomerases
Enzyme that catalyzes the joining of substrates in the presence of ATP
Ligases
Characteristics of enzymes
Not changed in the reaction
Do not change or alter the equilibrium of the reaction
Increase reaction rates by decreasing activation energy
Highly specific
Mostly proteins in nature
Significance of the Km
1) Substrate concentration at which half the active sites of the enzyme are filled up
2) Inverse measure of the affinity of the substrate for the enzyme
Reversible inhibitions of enzymatic reactions
Competitive
Non competitive
Uncompetitive
Type of inhibition wherein the inhibitor binds specifically at the active or catalytic site, where it competes with the substrate for binding
Competitive inhibition
Type of inhibition wherein the inhibitor binds a substance other than at the active or catalytic site
Non competitive
Type of inhibition wherein the inhibitor binds only to ES complexes at locations other than the catalytic site, modifying enzyme structure, making the inhibitor binding site available
Uncompetitive inhibition
Type of inhibition wherein the inhibition is reversed by increasing substrate concentration
Competitive inhibition
Type of inhibitor
Vmx: decrease proportionately to inhibitor concentration
Km: unchange
Non competitive inhibitor
Type of inhibitor
Vmax: decrease
Km: decrease
Uncompetitive inhibitor
Type of inhibitor
Vmax: unchange
Km: increase
Competitive inhibitor
Enzymes following Michaelis-Menten kinetics show (linear/hyperbolic/sigmoid) curve.
Hyperbolic
Allosteric enzymes exhibit (linear/hyperbolic/sigmoid) curve
Sigmoid
Methods of regulating enzyme activity
Feedback inhibition Allosteric (non-covalent) modification Covalent modification Zymogen activation Induction or repression of enzyme synthesis
Binding of modulator to allosteric site, which causes a conformational change in the regulatory enzyme, alters the activity of the enzyme
Allosteric modification
(Low/High) Activity
Dephosphorylating Acetyl Coa Carboxylase
High
(Low/High) Activity
Phosphorylating Glycogen synthase
Low
(Low/High) Activity
Phosphorylating Pyruvate dehydrogenase
Low
(Low/High) Activity
Dephosphorylating HMG CoA reductase
High
(Low/High) Activity
Phosphorylating Glycogen phosphorylase
High
(Low/High) Activity
Dephosphorylating Citrate lyase
Low
(Low/High) Activity
Dephosphorylating Phosphorylase b kinase
Low
(Low/High) Activity
Phosphorylating HMG CoA reductase kinase
High
(Low/High) Activity
Dephosphorylating HMG CoA reductase kinase
Low
(Low/High) Activity
Phosphorylating Phosphorylase b kinase
High
(Low/High) Activity
Phosphorylating Citrate lyase
High
(Low/High) Activity
Dephosphorylating glycogen phosphorylase
Low
(Low/High) Activity
Phosphorylasing HMG CoA reductase
Low
(Low/High) Activity
Dephosphorylating pyruvate dehydrogenase
High
(Low/High) Activity
Dephosphorylating glycogen synthase
High
(Low/High) Activity
Phosphorylating Acetyl CoA carboxylase
Low
Factors affecting enzyme activity
Temperature
pH
Substrate concentration
Co-factors
As the temperature increases (until the optimum temperature is reached), the reaction velocity or the enzyme activity (increases/decreases)
Increases
Beyond the optimum temperature, the reaction velocity/enzyme activity (increases/decreases) as the temperature increases
Decreases
Increasing the pH value will (increase/decrease) the reaction rate
Increase
But, beyond the optimum pH, the reaction rate will decrease
Cofactors (chlorides, bromides, iodides) ___ the rate of enzyme-catalyzed reactions
Increase
As the substrate concentration increases, the reaction velocity (increases/decreases)
Increases
Up to a certain point
Substate concentration at which half of the active sites of the enzyme are filled up
Km
The lower the Km, the ___ is the affinity
Higher
The higher the Km, the ___ is the affinity
Lower
Models of enzyme-substrate complex
Lock and Key Model
Induced Fit Model
