Enzymes
Metabolism and Enzymatic Reactions
Metabolism
• All living things need energy
• This energy is used by organisms to develop,
grown and reproduce
• Energy is used in chemical reactions to
perform this development, growth and
reproduction.
• METABOLISM is the sum of all the
biochemical reactions that occur in a cell.
• The energy-producing reactions within cells
generally involve the breakdown of complex
organic compounds to simpler compounds.
These reactions release energy and are called
catabolic reactions.
• Anabolic reactions are those that consume
energy while synthesizing compounds.
• ATP produced by catabolic reactions provides
the energy for anabolic reactions. Anabolic
and catabolic reactions are therefore coupled
(they work together) through the use of ATP.
An anabolic reaction
Energy
Catabolic and Anabolic
Reactions
ATP
ADP + Pi
Energy
A catabolic reaction
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• Metabolic reactions have
– REACTANTS, which are the substances that participate in a
reaction, and
– PRODUCTS, which are the resulting substances
A+B→C+D
• Within cells many reactions are often linked together
to create the products a cell needs from the reactants
it is able to acquire. These chains of reactions are
called METABOLIC PATHWAYS.
A→B→C→D→E→F→G
• In this process the products from one reaction become
the reactants for the next reaction.
A
B
C
D
E
F
• Metabolic pathways can branch so that
a product like D can become the
reactant in two different types of
reactions
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Enzymes
A
enzyme 1
B
enzyme 2
C
enzyme 3
enzyme 5
D
enzyme 4
E
F
• ENZYMES are protein molecules that help to
sped up, or catalyze, a specific reaction.
• The enzyme causes the reactants in a reaction
to associate with each other so that they will
react to for the products.
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Substrate
1
Active Site
• Reactants in an enzymatic
reaction are called
SUBSTRATES.
• An enzyme brings
substrates together to
speed up their reaction.
Enzyme
Product
Enzyme-Substrate Complex
2
3
Enzyme
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• Many enzymes require another non-protein
piece to function properly
– APOENZYME: protein portion of the enzyme. It’s
shape is what gives it the ability to only run a
single type of reaction
– COENZYME/COFACTOR: non-protein portion. The
portion that binds to the enzyme and then carries
a chemical group or electron of one or both
reactants.
• Apoprotein + Coenzyme(s) = Holoenzyme
(Haloenzyme)
Cofactors
• Many enzymes require a cofactor to assist in the
reaction. These "assistants" are nonprotein and
may be metal ions such as magnesium (Mg++),
potassium (K+), and calcium (Ca++).
• The cofactors bind to the enzyme and participate in
the reaction by removing electrons, protons , or
chemical groups from the substrate.
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Coenzymes
• Cofactors that are organic molecules are
coenzymes.
• Coenzymes are usually vitamins.
Vitamin
Niacin
B2 (riboflavin)
B1 (thiamine)
pyrophosphate
Pantothenic acid
12B12
Coenzyme Name
NAD+
FAD
Thiamine
Coenzyme A (CoA)
Cobamide coenzymes
Coenzyme
Enzyme
Enzyme
• Coenzymes are cofactors that are not protein.
• They bind to the enzyme and also participate
in the reaction by carrying electrons or
hydrogen atoms.
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Activation Energy
• Many reactions won’t occur unless there is an
input of energy added to start the reaction
• This ACTIVATION ENERGY causes the first reactant
molecules to collide with enough force to react.
They release energy which drives further
reactions.
• In the lab this is often achieved by adding heat to
increase the number of collisions that occur.
• Activation energy is often shown by the symbol
(Ea).
• Enzymes catalyze (speed up) reactions by
lowering the activation energy (Ea) required to
get the reaction started.
• They do this by bringing the substrates closer
together so they are able to react more easily.
Enzymes lower the amount of
activation energy needed for a reaction.
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Energy Released
Energy Supplied
Enzymes Lower Activation Energy
Activation energy
without enzyme
Activation energy
with enzyme
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• Because enzymes are made up of proteins
they require a specific substrate at a specific
temperature and a specific pH to work
properly.
• S.T.E.P.P
– S= SUBSTRATE (what substrate does it work on?)
– T= TEMPERATURE (at what temp does it work?)
– E= ENZYME (what is the name of the enzyme?)
– P=pH (at what pH does it work best?
– P=PRODUCT (what new chemical products form?)