ENZYMES
Enzymes are specialized protein molecules that act as catalysts. Catalysts
speed up the rate of a chemical reaction. Enzymes speed up reactions by
binding to the reactants known as substrates. The enzyme-catalyzed
reaction occurs at a location on the enzyme known as the active site. The
joining of the enzyme to the substrate produces an
enzyme-substrate complex. The enzyme – substrate complex is held
together by hydrogen bonds and weak ionic bonds. Substrates fit closely
into active sites because enzymes can adjust their shapes slightly to
accommodate the substrate. The change of shape in the active site to
accommodate the substrate is called induced fit. It is during the
formation of the enzyme-substrate complex that the reaction occurs.
Following the reaction, the enzyme releases the products.
By binding to their substrates,
enzymes are able to lower the
activation energy. Activation
Energy is the energy required for a
chemical reaction to occur.
CONDITIONS AFFECTING ENZYMES
1.
Enzyme Concentration – The rate of the reaction is proportional to
the enzyme concentration.
2. Substrate Concentration – As the concentration of the substrate
increases, the rate of reaction increases up to a point, then levels off.
This is called the saturation point.
3. pH – Each enzyme has an optimal temperature at which it works best.
Although typical enzymes have an optimal pH value of about 7, there
are exceptions.
4. Temperature - Each enzyme has an optimal temperature at which it
works best. Most human enzymes function best between 35 ºC and
50 ºC
ENZYME INHIBITION
A variety of substances inhibit enzyme
activity. COMPETITIVE INHIBITORS
are similar to the enzyme’s substrate and
thus are able to enter the enzyme’s
active site and block the normal
substrate from binding. Increasing the
concentration of the enzyme’s substrate
will reverse the process. Penicillin acts
as a competitive inhibitor by binding to
the active site of transpeptidase, the
enzyme involved in bacterial cell wall
construction, preventing bacterial cells
from dividing successfully.
NON COMPETITIVE INHIBITORS do not compete
with an enzyme’s substrate for the active site.
Instead they bind to the allosteric site which is
another site on the enzyme, causing a change in the
enzyme’s 3-d structure in such a way that it loses
affinity for its substrate. Substances that bind to
the allosteric sites may inhibit or stimulate an
enzyme’s activity. Those that stimulate the action of
enzymes are known as activators.
Feedback inhibition is a type of noncompetitive inhibition used by
cells to control metabolic pathways involving a series of sequential reactions,
each catalyzed by a specific enzyme. In feedback inhibition, an end product
allosterically inhibits an enzyme that catalyzes a reaction occurring earlier in
the process.
The final manner in which enzymes can be regulated comes in the form of
nonprotein cofactors and coenzymes. Cofactors are often metals, such as
iron, copper, zinc, and magnesium. Cofactors consist of inorganic ions such
as Cu2+, Zn2+ or Fe2+. Although your body may need only very small amounts
of these metals, they are essential. Cofactors, can aid in binding the
substrate to the enzyme or in stabilizing the enzyme in an active
conformation. Coenzymes are organic cofactors derived from vitamins.
As a result, lack of a particular vitamin can impair the action of its
corresponding enzyme and lead to disease. Nicotinamide adenine
dinucleotide (NAD+) is a derivative of vitamin B3. Both coenzymes NAD+ and
FAD (flavin adenine dinucleotide) serve as electron acceptors in redox
reactions. They carry electrons from one enzyme to another.
COMMERCIAL AND INDUSTRIAL USES OF ENZYMES
 The starch-processing industry is one of the largest industrial users
of enzymes. Starch is converted to glucose syrups by enzymatic
hydrolysis
 Restriction enzymes are used in DNA fingerprinting to cut DNA at
specific places. Applications include paternity testing, murder trials
and identification of people.
 The enzyme lactase hydrolyzes lactose into glucose and galactose and
is often added to lactose free milk.
FEEDBACK INHIBITION
The amount of product is kept tightly controlled by the feedback inhibition
process. Feedback inhibition is one of the most common control mechanisms used
in metabolism.
Feedback inhibition Animation
Enzymes Animation
Catalase Lab Bozeman Science