CH. 6 (Unit H) Metabolism :
Energy and Enzymes
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Forms of Energy
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These forms of energy are important to life:
– chemical
– radiant (examples: heat, light)
– mechanical
– electrical
Energy can be transformed from one form to
another.
Chemical energy is the energy contained in the
chemical bonds of molecules. It is the main
energy form we are interested in studying.
Energy that is stored is called potential energy.
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Laws of Thermodynamics
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1st law: Energy cannot be created or destroyed.
– Energy can be converted from one form to another. The sum of the
energy before the conversion is equal to the sum of the energy after the
conversion.
– Example: A light bulb converts electrical energy to light energy and
heat energy. Fluorescent bulbs produce more light energy than
incandescent bulbs because they produce less heat.
C6H12O6 + 6O2  6CO2 + 6H2O + Energy
300 J + 200 J  100 J + 100 J + 300 J
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Laws of Thermodynamics
2nd law: Some usable energy dissipates (leaves) during transformations
and is lost as heat.
During changes from one form of energy to another, some usable
energy dissipates, usually as heat. The amount of remaining usable
energy therefore decreases.
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Energy is required to form bonds – ANABOLIC
Reactions (endothermic/endergonic)
Atoms or molecules + Energy
Energy
Energy
Example: Taking amino acids and
building them into a protein.
Synthesis requires energy input
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Larger molecule
The energy that was used
to form the bonds is now
stored in the bonds of this
molecule.
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Energy Supplied
Energy Released
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Anabolic Reactions
Products
Anabolic reactions consum
energy. ENDERGONIC or
ENDOTHERMIC
Substrates
(Reactants)
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Energy is released when bonds are
broken – CATABOLIC Reactions
(Exothermic/exergonic)
Larger macromolecules are hydrolyzed to give rise to smaller
monomers. Energy is released.
Example : When the body take triglycerides and breaks them into
7Glycerol and Three Fatty Acids
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Energy is released when bonds are
broken.
When bonds break, energy
is released. It may be in a
form such as heat or light or
it may be transferred to
another molecule.
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Energy
Energy
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Energy Supplied
Energy Released
Catabolic Reactions
Substrate
(Reactant)
Catabolic reactions release
energy. EXERGONIC
EXOTHERMIC
When
bonds are broken, energy is released.
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Catabolic and Anabolic Reactions
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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.
Diagram: next slide
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An anabolic reaction
Energy
Catabolic and Anabolic
Reactions
ATP
ADP + Pi
Energy
A catabolic reaction
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ENTROPY Calculation
Entropy = is a mathematicallydefined thermodynamic
quantity that helps to account
for the flow of energy through
a thermodynamic process such
as a chemical reaction
G = Eproducts - Ereactants
Example : if Reactants have 500 Joules of usable energy but your products end up only
having 200 Joules of usable energy. Then 300 Joules were released.
According to the example: G = Eproducts - Ereactants
So 300 J – 500 J = - 200 Joules. A negative number indicates a
exothermic/exergonic reaction
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One very important energy storing and
releasing molecule is ATP
3 phosphate groups
A
Base (adenine)
Sugar (ribose)
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ATP Stores Energy
The phosphate bonds are
high-energy bonds.
Energy
A
ATP
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Breaking the bonds
releases the energy.
A
ADP
+ Pi + Energy
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ATP is Recycled – In the “ATP CYCLE”
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ATP (Adenosine Triphosphate) is an energy-containing
molecule used to supply the cell with energy. The energy
used to produce ATP comes from glucose or other highenergy compounds.
ATP is continuously produced and consumed as
illustrated below.
ADP + Pi + Energy  ATP + H2O
(Note: Pi = phosphate group)
ATP
Energy
Energy
(from glucose or
other high-energy
compounds)
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ADP + Pi
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The ATP Cycle can be coupled to drive other
anabolic reactions, or coupled with catabolic
reactions to form ATP from ADP + P.
ATP
ADP + Pi
In this diagram, energy from
breakingATP
bonds in this
molecule is used to form ATP.
Energy
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Energy
ATP
ADP + Pi
The energy in ATP can be
ATP bonds in other
used to form
molecules.
Energy
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ATP (Adenosine Triphosphate)
NH2
Base (adenine)
N
OO-
P
O
HC
N
O-
OO
P
C
O
O
P
O
O
C
CH
C
N
CH2 O
C
C
3 phosphate groups
N
C
H
H
C
CH
OH
OH
Ribose
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METABOLISM : THE
SUM OF ALL THE
ANABOLIC AND
CATABOLIC REACTIONS
THAT TAKE PLACE
INSIDE ALL THE CELLS
OF AN ORGANISM.
- The rate of these reactions
gives rise to one’s
METABOLIC RATE
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Enzymes
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Catalysts are substances that speed up chemical reactions. Organic
catalysts (contain carbon) are called enzymes.
Enzymes are specific for one particular reaction or group of related
reactions.
Many reactions cannot occur without the correct enzyme present.
They are often named by adding "ase" to the name of the substrate.
Example: Dehydrogenases are enzymes that remove hydrogen. – Helicase,
Maltase, DNA Polymerase, Reverse Transcriptase etc.
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Rate of Reaction
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Reactions with enzymes are up to 10
billion times faster than those without
enzymes.
Enzymes typically react with between
1 and 10,000 molecules per second.
Fast enzymes catalyze up to 500,000
molecules per second.
Substrate concentration, enzyme
concentration, Temperature, and
pH affect the rate of enzyme
reactions.
They increase reaction rate by
lowering the amount of Ea required!
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Metabolic reactions use enzymes
A high-energy molecule (substrate) is used to transfer a
phosphate group to ADP to form ATP.
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Substrate
Enzymes
Enzymes are organic
catalysts.
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Active Site
Enzyme
Product
Enzyme-Substrate Complex
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Enzyme
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Cofactors
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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
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Cofactors that are organic molecules are
coenzymes.
Coenzymes are usually vitamins.
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Vitamins are Coenzymes
Vitamin
Niacin
B2 (riboflavin)
B1 (thiamine)
Pantothenic acid
B12
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Coenzyme Name
NAD+
FAD
Thiamine pyrophosphate
Coenzyme A (CoA)
Cobamide coenzymes
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Coenzymes
Coenzyme
Enzyme
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Enzyme
Coenzymes are cofactors that are non protein.
They bind to the enzyme and also participate in the
reaction by carrying electrons or hydrogen atoms.
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Energy Released
Energy Supplied
Activation Energy
Activation Energy
In either kind of reaction,
additional energy must be
supplied to start the
reaction. This energy is
called activation energy.
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Energy Released
Energy Supplied
Activation Energy
Activation Energy
An example of activation
energy is the spark
needed to ignite gasoline.
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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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When studying enzymes in upcoming units
remember to watch your S.T.E.P.P s
P = pH – OPTIMAL pH
P = PRODUCT NAME
E = ENZYME NAME
T = OPTIMAL TEMERATURE
S = SUBSTRATE NAME
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Induced Fit Theory – Most current
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An enzyme-substrate complex forms
when the enzyme’s active site binds with
the substrate like a key fitting a lock.
The substrate molecule does not fit
exactly in the active site. This induces a
change in the enzymes conformation
(shape) to make a closer fit.
After the reaction, the products are
released and the enzyme returns to its
normal shape.
Only a small amount of enzyme is needed
because they can be used repeatedly.
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Lock and Key Theory
The older theory of how enzymes work was that the enzyme has an
already perfect active site shape for that particular substrate. Just like only
the perfect key will fit the complimenting lock
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Metabolic Pathways
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Metabolism refers to the chemical reactions that
occur within cells.
Reactions occur in a sequence and a specific enzyme
catalyzes each step.
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Notice that C can produce either D or F.
This substrate has two different enzymes
that work on it.
Metabolic Pathways
A
enzyme 1
B
enzyme 2
C
enzyme 3
enzyme 5
D
enzyme 4
E
F
Enzymes are very specific. In this case
enzyme 1 will catalyze the conversion of
A to B only.
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A Cyclic Metabolic Pathway
In this pathway, substrate “A” enters
the reaction. After several steps,
product “E” is produced.
A
B
F
A+FB
C
BCD
DF+E
E
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D
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Feedback Inhibition
The goal of this hypothetical metabolic
pathway is to produce chemical D from A.
A
enzyme 1
B
enzyme 2
C
enzyme 3
D
B and
are intermediates.
Enzyme regulation
by C
negative
feedback inhibition is
similar to the thermostat example. As an enzyme's product
The next several slides will show how
accumulates, it turns off the enzyme just as heat causes a
feedback inhibition regulates the amount
thermostat to turn off the production of heat.
of D produced.
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Feedback Inhibition
C and D will decrease
because B is needed to
produce C and C is
needed to produce D.
The amount of B in the cell will
decrease if enzyme 1 is inhibited.
A
enzyme 1
X
B
X
enzyme 2
C
X
enzyme 3
D
X
Enzyme 1 is structured in a way that causes it
to interact with D. When the amount of D
increases, the enzyme stops functioning.
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Feedback Inhibition
B, C, and D can now be synthesized.
A
enzyme 1
B
X
enzyme 2
C
X
enzyme 3
D
X
When the amount of D
drops, enzyme 1 will no
longer be inhibited by it.
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Feedback Inhibition
A
enzyme 1
X
B
enzyme 2
C
enzyme 3
D
As D begins to increase, it inhibits enzyme
1 again and the cycle repeats itself.
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The End
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