Enzymes are biological catalysts Enzymes are proteins that: Increase the rate of reaction by

lowering the energy of activation. Catalyze nearly all the chemical

reactions taking place in the cells of the body.

Have unique three-dimentional shapes that fit the shapes of reactants.

The name of an enzyme : Usually ends in –ase. Identify the reacting substance. Ex: sucrase catalyzes the reaction of

sucrose. Describes the function of the enzyme. Ex: oxidases catalyze oxidation. Could be a common name , particularly

for the digestion enzymes such as pepsin and trypsin.

ExamplesExamples

To react with lactoselactose.

lactlactaseaseTo remove carboxylcarboxyl from pyruvatepyruvate.

pyruvate pyruvate decarboxyldecarboxylasease

-ase-ase ending

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it reacts+

The active site: Is a region within an enzyme that

fits the shape of molecules called substrates.

Contains amino acid R groups that align and bind the substrate.

Release products when the reaction is complete.

The proper fit of a substrate (S) in an active site forms an enzyme-substrate (ES) complex.

E + S ES Within the (ES) complex, the reaction occurs

to convert substrate to Product (P).

  ES E + P The products which are no longer attracted

to the active site, are released.  Overall substrate is converted to products.

E + S ES E + P

 

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Enzymes may recognize and catalyze:

A single substrate. A group of similar substrates. A particular type of bond.

Classification of Enzymes

Enzymes are classified by the reaction they catalyze.Class Type of Reactions catalyzedOxidoreductases Oxidation-reductionTransferases Transfer groups of atomsHydrolases HydrolysisLyases Add atoms/remove atoms to or

from a double bondIsomerases Rearrange atomsLigases Use ATP to combine small molecules

Oxidoreductases and Transferases

Hydrolases and Lyases

Isomerases and Ligases

Isoenzymes

Catalyze the same reaction in different tissues in the body.

LDH, which converts Lactate to Pyrovate, have 5 isoenzymes.

Isoenzymes

Diagnostic Enzymes The levels of diagnostic enzymes determine the amount

of damage in tissues.

Diagnostic Enzymes

Levels of enzymes CK, LDH, and AST Are elevated following

a heart attack. Are used to determine

the severity of the attack.

Lock and key model In the lock and key model of

enzyme action: The active site have a rigid shape. Only substrates with the matching

shape can fit. The substrate is a key that fits the

lock of the active site.

Induced fit model In the induced fit model: The active site is flexible, not rigid. The shape of the enzyme active site

and substrate adjust to maximum the fit, which improve catalysis.

There is a greater range of substrate specificity.

Temperature. pH. Substrate concentration. Inhibitors.

COMPETITIVE INHIBITION

NON-COMPETITIVE INHIBITION

Classification of Enzymes• Oxidoreductases catalyze redox reactions

– Reductases

– Oxidases

• Transferases transfer a group from one molecule to another– Transaminases catalyze transfer of an amino group

– Kinases transfer a phosphate group

Classification of Enzymes

• Hydrolases cleave bonds by adding water

– Phosphatases– Peptidases – Lipases

• Lyases catalyze removal of groups to form double bonds or the reverse break double bonds

– Decarboxylases– Synthases

Classification of Enzymes• Isomerases catalyze intramolecular

rearrangements – Epimerases – Mutases

• Ligases catalyze a reaction in which a C-C, C-S, C-O, or C-N bond is made or broken