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Biology 12
Cellular Metabolism
Enzymes
Name: __________________
Blk: ____ Date: __________
A. Cellular Metabolism: Refers to all of the ________________-mediated chemical
reactions within a cell.
Two main types of reactions
1. Anabolic metabolism – to _________________
2. Catabolic metabolism – to _________________
B. Activation Energy:
 The ____________ needed for a ______________
reaction to take place.
 The energy needed to get over the ________
 The _________ of a reaction depends on the
_____________of activation ______________ required
to break existing ___________.
•In either kind of reaction below, additional energy must be supplied to start the reaction.
•This energy is the 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:
 Function: A catalyst ____________ the amount of
energy required (by stressing chemical bonds)
 A substance that ___________ up chemical
reactions, but is not part of the _____________.
 _____________ are the cell’s catalysts
• Enzymes provide an ________________
path involving a __________ hill
D. Enzymes
 Cells contain many different enzymes, each
of which ____________ a different
______________.
 They cannot speed up reactions that would
______ normally ___________ on their own.
 A given enzyme interacts with a set of reactants
(called _____________) or occasionally with a
few closely related ones.
 Shape: Enzymes are mostly globular
(_____________) proteins with one or more
invaginations on their surface called the
______________ _______.
 Induced Fit: Proteins are not _________,
so the enzyme may _______ a little allowing an ___________ fit.
 Denaturing of an enzyme is the “________ of the ___________ site.”
Lock and Key theory:
In order for the catalysis to occur the substrate must fit perfectly into this depression.
4 Factors that affect Enzyme Activity:
1) Temperature:
 Human enzymes work best between ____ and _____
 The _______ of a chemical reaction is reduced by _______ for every _____ drop.
 Below this temperature the protein is not as ___________to allow induced fit
and becomes ___________________.
 This is not the same as denaturation, as deactivation is
________________.
 Above this temperature, the _________ are too weak
 The upper limit of enzyme activity before being denatured is ____
 Damage caused by mild ___________ may in some cases be
______________
 But continued _____________ would continue to denature more
and more of the enzyme until no __________ enzyme remains
 Ex: amylase would be completely denatured at 80oC
2) pH:
 Optimum pH is between ___ and ____ (except ________ which prefers a pH of 2)
 Straying from these pH values ____________ protein by disrupting bond charges,
especially ____________ between R-groups of adjacent amino acids.
 The result is a lost of the __________ site.
3) Inhibitors:
a) Competitive Inhibitors –_____________ active sites
b) Non-competitive Inhibitor: binds to the enzyme and ________ the shape of the
_________ site, so the substrate no longer fits. (Ex: heavy metal
poisoning lead
or mercury)
4) Cofactors: Often enzymes use additional chemical components to aid catalysts.
a) Metal ions: they draw ______________ from ______________ molecules.
o Ex: carboxypeptidase has a zinc ion that draws electrons from the bonds
joining amino acids.
o This is why we need trace elements (____________) for good health
b) Coenzymes: non-protein _____________ molecules used as cofactors
o Ex: ______________
Note: coenzymes shuttle ____________ in the form of an atom form one place in the cell
to another.