Transcript Enzymes - myndrs.com

Enzymes
• The energy needed to get over the hill
• Enzymes provide alternative path
involving a lower hill
• Activated complex
A. Cellular Metabolism
•
•
Refers to all of the enzyme-mediated
(chemical) reactions within a cell.
Two main types of reactions
1. Anabolic metabolism – to build
2. Catabolic metabolism – to break down
B. Activation Energy
• The energy
needed for a
chemical
reaction to take
place.
• The energy
needed to get
over the hill
B. Activation Energy
• the speed of a reaction depends on the amount of
activation energy required to break existing bonds
• In either kind of reaction, additional energy must be
supplied to start the reaction.
• This energy is the activation energy.
B. Activation Energy
• Endergonic - Refers to a chemical
reaction that consumes energy. (anabolic)
• Exergonic - Describes a chemical
reaction that releases energy in the form
of heat, light, etc. (catabolic)
C. Catalyst
• A catalyst lowers the amount of energy
required (by stressing chemical bonds)
• A substance that speeds up chemical
reactions, but is not part of the products.
• Enzymes are the cell’s catalysts
C. Catalyst
• Enzymes provide alternative path involving a
lower hill
D. Enzymes
• Cells contain many different enzymes,
each of which catalyzes a different
reaction.
• They cannot speed up reactions that
would not normally occur on their own.
• A given enzyme interacts with a set of
reactants (called substrates) or
occasionally with a few closely related
ones.
D. Enzymes
• Enzymes are mostly
globular (tertiary)
proteins with one or
more invaginations
on their surface
called the active site
Lock and Key Theory:
In order for the catalysis
to occur the substrate
must fit perfectly into this
depression.
D. Enzymes
Lock and Key Theory:
D. Enzymes
• Induced Fit:
• Proteins are not rigid, so the enzyme may
give a little allowing an induced fit.
D. Enzymes
• Denaturing of an enzyme is the “loss of
the active site.”
Factors that affect Enzyme Activity:
1. Temperature:
•
•
•
Human enzymes work best between 35o
and 40oC
The rate of a chemical reaction is reduced
by half for every 10oC drop.
Below this temperature the protein is not
flexible to allow induced fit and becomes
deactivated.
•
This is not the same as denaturation, as
deactivation is reversible.
Factors that affect Enzyme Activity:
1. Temperature:
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•
•
•
•
Above this temperature, the H-bonds are too weak
The upper limit of enzyme activity before being
denatured is 40oC
Damage caused by mild heating may in some cases
be reversible
But continued warming would continue to denature
more and more of the enzyme until no active
enzyme remains
Ex: amylase would be completely denatured at
80oC
Factors that affect Enzyme Activity:
2. pH:
– Optimum pH is between 6 and 8 (except
pepsin which prefers a pH of 2)
– Straying from these pH values denatures
protein by disrupting bond charges, especially
H-bonds between R-groups
– The result is a lost of the active site.
Factors that affect Enzyme Activity:
3. Inhibitors:
a) Competitive Inhibitors –block active sites
A competitive inhibitor
binds reversibly to the
enzyme, preventing
the binding of the
substrate.
On the other hand,
binding of substrate
prevents binding of the
inhibitor, thus substrate
and inhibitor compete
for the enzyme.
Factors that affect Enzyme Activity:
3. Inhibitors:
b) Non-competitive Inhibitor:
binds to the enzyme and alters the shape
of the active site, so the substrate no
longer fits.
Ex: heavy metal poisoning
(lead or mercury)
Factors that affect Enzyme Activity:
4. Cofactors: Often enzymes
use additional chemical
components to aid
catalysts.
a) Metal ions: they draw
electrons from substrate
molecules.
–
–
Ex: carboxypeptidase has a
zinc ion that draws
electrons from the bonds
joining amino acids.
This is why we need trace
elements (minerals) for
good health
Factors that affect Enzyme Activity:
4. Cofactors: Often enzymes use
additional chemical components to aid
catalysts.
b) Coenzymes: non-protein organic molecules
used as cofactors
•
Ex: vitamins
Note: coenzymes shuttle energy in the form
of an atom form one place in the cell to
another.