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By Levi Clancy for Student Reader on

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Enzymes are proteins that lower activation energy.

They are catalysts. They accelerate reactions, but do not make them happen. They are highly specific.

Catalysts must: 1) Increase reaction rate. 2) Be reusable. 3) Catalysts will not contribute to spontaneity.

Enzyme Inhibition

Inhibitors stop enzyme-substrate interaction.

There are two kinds of inhibitors:

Competitive inhibitors

Competitive inhibitors bind the active site, but if [sub] increases then the inhibitor is outcompeted. The Vmax is not reached right away because there is still an inhibitor.

There would be a decreased slope bu at [sub] rises then Vmax is eventually reached.

Noncompetitive inhibitors

Noncompetitive inhibitors bind the allosteric site, causes a conformational change and cannot be outcompeted. No matter what you do, you will never raise the Vmax you once had. Hence, there will be same increase as with competitive, but level off sooner.

Always guess negative feedback because almost everything is negative feedback. Positive feedback wants you to make MORE not LESS. More signals sent, more amplification, more product, more more. Positive feedback can very easily get out of control.

Enzyme Classes and Subclasses


Oxidoreductases catalyze oxidation-reduction reactions.

DehydrogenaseTransfer of a hydride ion.
OxidaseO2 is the e- acceptor.

Transferases catalyze the transfer of a functional group from one compound to another.

KinasePhosphoryl transfer from a nucleotide (ie, ATP).
AminotransferaseTransfer of an amino group between compounds.

Hydrolases catalyzes hydrolysis, the cleavage of a single bond by addition of water.

PhosphataseReleasing of free Pi by hydrolysis of a bond to a phosphoryl group.
PeptidaseHydrolysis of a peptide bond.
GlycosidaseHydrolysis of a glycosidic bond.
LipaseHydrolysis of a bond in a lipid.

Lyases catalyze the breaking of a single bond with the formation of a double bond.


Movement a functional group from one position on a molecule to another.


Bond formation coupled to nucleotide triphosphate hydrolysis.