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Concept 8.1: An organism’s metabolism transforms
matter and energy, subject to the laws of thermodynamics
• Metabolism is
the totality of an
organism’s
chemical
reactions
including matter
and energy.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway is a series of chemical
reactions that begins with a specific molecule and
ends with a product
Enzyme 1
A
Enzyme 2
B
Reaction 1
Enzyme 3
C
Reaction 2
D
Reaction 3
Starting
molecule
Product
• Each step is catalyzed by a specific enzyme
• http://www.youtube.com/watch?v=QJzAvTAL9WI
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Metabolic Pathways:
Catabolic and Anabolic Pathways
• 1- Catabolic pathways breakdown complex
molecules to form simpler molecules &
liberate energy that is available to the cell.
• e.g: in cellular respiration:
Glucose breaks down to CO2 and
H2O & energy is released.
– some of the released energy is saved as ATP and
used by the cell as energy currency.
– most of the energy is released as heat energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Metabolic Pathways:
Catabolic and Anabolic Pathways
• 2- Anabolic pathways consume energy to
build complex molecules from simpler ones
• Examples:
– making sugars from CO2 and H2O
– making starch from glucose
– making proteins from amino acids.
– making fats from fatty acids and glycerol
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Forms of Energy
• Energy is the capacity to cause change.
• Energy exists in various forms.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Forms of Energy
• Kinetic energy is energy associated
with motion.
• Potential energy is:
– energy that matter possesses
because of its location or structure.
– It’s energy at rest, but has the
potential to do work.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy can be converted from one form to another
Energy conversion!!!!
Wait, I can explain that.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
http://www.youtube.com/
watch?v=vl4g7T5gw1M
Energy can be converted from one form to another
Energy conversion!!!!
What’s going on up there?
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
On the platform,
the diver has
more potential
energy.
Diving converts
potential
energy to
kinetic energy.
Climbing up converts
kinetic energy of
muscle movement to
potential energy.
In the water, the
diver has less
potential energy.
The First Law of Thermodynamics
• Thermodynamics is the study of energy
transformations
• According to the first law of thermodynamics,
the energy of the universe is constant
– Energy can be transferred and transformed
– Energy cannot be created or destroyed
• The first law is also called the principle of
conservation of energy.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Second Law of Thermodynamics
• During every energy transfer or transformation, some
energy is unusable, often lost as heat
• According to the second law of thermodynamics, every
energy transfer or transformation increases the entropy
(disorder) of the universe.
• Living cells unavoidably convert organized forms of energy
to heat
Heat
Chemical
energy
First law of thermodynamics
CO2
H2O
Second law of thermodynamics
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Enzymes speed up metabolic reactions by lowering
energy barriers
• A catalyst is a chemical agent that speeds up a
reaction without being consumed by the reaction
• An enzyme is a catalytic protein
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Enzymes
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Activation Energy Barrier
• Every chemical reaction between molecules
involves bond breaking and bond forming
• The initial energy needed to start a chemical
reaction is called the free energy of activation, or
activation energy (EA)
• Activation energy is often supplied in the form of
heat from the surroundings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-14
A
B
C
D
Free energy
Transition state
A
B
C
D
EA
Reactants
A
B
DG < O
C
D
Products
Progress of the reaction
Enzymes lower the activation energy of a reaction
Enzymes lower the activation energy of a
reaction, increase the speed of a reaction
(millions of reactions per minute!)
Enzymes do not affect the change in free-energy (∆G).
http://www.youtube.com/watch?v=Dd1yi2aVoOc
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Enzymes lower the activation energy of a reaction
Free energy
Course of
reaction
without
enzyme
EA
without
enzyme
EA with
enzyme
is lower
Reactants
Course of
reaction
with enzyme
DG is unaffected
by enzyme
Products
Progress of the reaction
Figure 3.12 Activation Energy Initiates
Reactions
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Substrate Specificity of Enzymes
• The reactant that an enzyme acts on is called the
enzyme’s substrate
• The enzyme binds to its substrate, forming an
enzyme-substrate complex
• The active site is the region on the enzyme where
the substrate binds
• Induced fit of a substrate brings chemical groups
of the active site into positions that enhance their
ability to catalyze the reaction.
•
http://www.youtube.com/watch?v=V4OPO6JQLOE&feature=related
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 8-16
Substrate
Active site
Enzyme
Enzyme-substrate
complex