Enzyme : A Biological
Catalyst
Metabolism
Is the totality of an organism’s
chemical reactions
Arises from interactions between
molecules
A metabolic pathway has many steps
That begin with a specific molecule
and end with a product
That are each catalyzed by a specific
enzyme
Enzyme 1
Enzyme 2
Enzyme 3
Organization of the Chemistry of Life
into Metabolic Pathways
A
B
C
D
Reaction 1
Reaction 2
Reaction 3
Starting
molecule
Product
Catabolic pathways
Break down complex molecules into
simpler compounds
Release energy
Anabolic pathways
Build complicated molecules from
simpler ones
Consume energy
Energy
Is the capacity to cause change
Exists in various forms, of which
some can perform work
The living cell
Is a miniature factory where
thousands of reactions occur
Converts energy in many ways
Kinetic energy
Is the energy associated with motion
Potential energy
Is stored in the location of matter
Includes chemical energy stored in
molecular structure
• Energy can be converted
– From one form to another
On the platform, a 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, a diver has
less potential energy.
The Regeneration of ATP
• Catabolic pathways
– Drive the regeneration of ATP from ADP
and phosphate
ATP synthesis from
ADP + P i requires energy
ATP hydrolysis to
ADP + P i yields energy
ATP
ADP + P i
Energy for cellular work
(endergonic, energy-
consuming processes)
Energy from catabolism
(exergonic, energy yielding
processes)
• The three types of cellular work
– Are powered by the hydrolysis of ATP
P
Membrane
protein
Motor protein
P i
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
ADP
(c) Chemical work: ATP phosphorylates key reactants
ATP
(b) Transport work: ATP phosphorylates transport proteins
Solute
P
P i
transported
Solute
Glu
Glu
NH3
NH2
P i
P i
+
+
Reactants: Glutamic acid
and ammonia
Product (glutamine)
made
+
P