Transcript Enzymes - Antelope Valley College

Enzymes
Most enzymes are globular proteins
Active site: the region of an enzyme surface
to which a specific set of substrates binds.
Substrate: ( the reactant ) a molecule upon
which an enzyme acts.
A substrate molecule must fit precisely into
an active site.
Cells employ enzymes to lower
activation energies
By bringing two substrates together in the
correct orientation, or by stressing particular
chemical bonds of a substrate, an enzyme
lowers the activation energy required for
new bonds to form.
Enzymes speed up the rate of
chemical reactions
Let us consider this reaction:
CO2 + H2O ----- H2CO3
carbon dioxide + water -----
carbonic acid
The reaction is very slow in the absence of
an enzyme called carbonic anhydrase.
Perhaps 200 molecules of carbonic acid are
formed in an hour in a cell.
Under the same conditions, but with the
presence of carbonic anhydrase, an
estimated 600,000 molecules of carbonic
acid form every second, thus the enzyme
increases the reaction rate by more than 10
million times.
Enzymes are not consumed in the
chemical reactions
Because the enzyme itself is not changed or
consumed in the reaction, only a small
amount is needed, and it can be used over
and over.
How Enzymes Work
View how enzymes work-animation in my
website
Enzymes are specific in their
choice of substrate
This specificity is due to the active site of
the enzyme, which is shaped so that only a
certain substrate will fit into it.
Enzymes typically catalyze only one or a
few chemical reactions.
Factors Affecting Enzyme Activity
Temperature: Most human enzymes
have temperature optima between 35 C
and 40 C.
pH: Most enzymes have a pH optimum;
it usually lies in the range of pH 6 to 8.
Cofactors and Coenzymes
The activity of enzymes is often
facilitated by cofactors, which can be
metal ions or other substances.
Cofactors that are nonprotein organic
molecules are called coenzymes