Dec 20, 2015
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