Enzymes Flashcards
Competitive inhibitors
Inhibitor is similar to the substrate, and binds at the active site.
Overcome by adding more substrate.
Km increases (b/c it takes more substrate to reach 1/2Vmax,)
Vmax is unchanged (active enzymes still have the same rate.)
Noncompetetitive inhibitors
Inhibitor bind to the enzyme or enzyme-substrate complex at allosteric site with equal affinity.
Not overcome by adding more substrate, b/c the inhibitor is not competing with the substrate for the active site.
Vmax is decreased (less enzyme available to react,)
Km is unchanged.
Mixed inhibitors
Inhibitors has a different affinity for the enzymes and enzyme-substrate complex.
Binds at allosteric site.
Increases or decreases Km based on which it has affinity for (increased Km with affinity for enzyme-substrate complex, decreased if prefers enzyme.)
Vmax is decreased.
Uncompetitive inhibitors
Bind to enzyme-substrate complex and lock substrate in.
Decreases both Km and Vmax.
Lines for no inhibitors and inhibitors present on LB plot parallel.
Zymogens
Inactive forms of enzyme. Allows body to use enzyme only when needed.
Irreversible inhibition
Permanently alters the enzyme so that it cannot perform it’s function, and active site is not available to substrate.
In order to reverse the effects of this type of inhibitor, more enzyme must be created.
Allosteric enzymes
Have multiple binding sites, including an allosteric site, which regulates the availability of the active site.
Michealis-Menten plots have S-shaped curve b/c when an activator binds to the allosteric site, the affinity increases.
Covalently modified enzymes
Enzymes that can be activated or deactivated by phosphorylation, dephosphorylation, or glycosylation.
Glycosylation tags enzymes for transport.
Cooperativity
Enzymes with multiple active sites have S-shaped curve in M-M plot due to increased activity with substrate binding.
Binding of substrate to one active site causes active sites of other subunits to transform from T (low affinity tense state) to R (high-affinity relaxed state.)
Cofactors
Inorganic molecules/metal ions needed for enzyme activity.
Typically participate in catalysis through protonation, deprotonation, or ionization.
Coenzymes
Organic molecules needed for enzyme activity.
Typically participate in catalysis through protonation, deprotonation, or ionization.
Mostly vitamins and their derivatives (NAD+, FAD, coenzyme A)
Oxidoreductases
Catalyze redox reactions.
ex. enzymes with dehydrogenase, reductase, oxidase in their names.
Transferases
Catalyze movement of a functional group from one molecule to another.
Includes kinases (transfer a phosphate group.)
Hydrolases
Catalyze breaking a compound in to 2 molecules using addition of water.
ex. peptidases, lipases, nucleases
Lyases
Catalyze breaking of a compound in to 2 molecules.
Because enzymes can catalyze their reverse reactions, lyases are also involved in the synthesis of 2 molecules into a single molecule (synthases.)
