Enzymes Flashcards
Most enzymes are…
Globular proteins
Examples of enzyme cofactors
Inorganic (Mg+, Zn+), organic (called coenzymes), prosthetic groups, apoenzymes.
Types of coenzymes
Coenzyme A and NAD+.
Coenzyme bound to enzyme protein =
Prosthetic group.
Apoenzyme
Without coenzyme
Holoenzyme
With coenzyme.
How does an apoenzyme become active
By binding of coenzyme or cofactor to enzyme. Holoenzyme is formed when it binds to the active site.
Oxidoreductases
Catalyze the transfer of electrions.
Transferases
Catalyze group transfer reactions.
Hydrolases
Catalyze hydrolysis reactions.
Lyases
Catalyse cleavage of C-C, C-O, and C-N or other bonds by elimination. Leave behind double bonds or rings.
Isomerases
Catalyze the transfer of groups within molecules to yield isomeric forms.
Ligases
Catalyze the formation of C-C, C-S, C-O and C-N bonds by condensation reaction coupled to cleavage of ATP or similar cofactor.
Enzymes do not…
Affect equilibrium, cannot change free energy.
Enzymes do affect…
Rates of reaction, decrease activation energy.
How do enzymes lower activation energy?
They organize reactive groups into close proximity and proper orientation (into a fairly rigid ES complex) by using enzyme substrate binding energy.
Enzyme active sites are complimentary too…
The transition state of the reaction.
Enzyme substrate binding results in…
Reduction of entropy, hindering the reaction.
Acid-base catalysis
Give and take protons
Covalent catlysis
Change reaction paths. Requires a nucleophile on the enzyme
Metal ion catalysis
Use redox cofactors, pKa shifters. Stabilizes negative charges.
In steady state conditions…
ES formed = ES consumed
ES association and dissociation depend on…
Constants (K) which reflect E and E properties.
Reaction rate is proportional to…
ES complex.
