An Organism’s Metabolism
Transforms Matter and Energy,
Subject to the Laws of
Thermodynamics
Potential and Kinetic Energy:
Cheetah at Rest and Running
Energy is lost
as heat
Potential and Kinetic Energy:
First Law of Thermodynamics: Energy
Can Neither Be Created or Destroyed
Second Law of Thermodynamics:
Every Energy Transfer Increases the
Disorder (Entropy) of the Universe.
The Free Energy Change of a
Reaction Tells Us Whether the
Reaction Occurs Spontaneously
∆G = G Final State – G Initial State
The Relationship of Free Energy to
Stability, Work Capacity, and
Spontaneous Change
Energy Changes in Exergonic
(energy releasing) and Endergonic
(energy storing) Reactions
Disequilibrium and Work in Closed and
Open Systems
• Cells in our body experience a
constant flow of materials in
and out, preventing metabolic
pathways from reaching
equilibrium
(b)
An open hydroelectric
system. Flowing water
keeps driving the generator
because intake and outflow
of water keep the system
8.7
fromFigure
reaching
equilibrium.
∆G < 0
ATP powers cellular work by
coupling exergonic reactions
to endergonic reactions
• A cell does three main kinds
of work:
– Mechanical
– Transport
– Chemical
•
• The three types of cellular work
are powered by the hydrolysis
of ATP
P
i
P
Motor protein
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
+
ATP
P
P
Solute
P
Solute
transported
(b) Transport work: ATP phosphorylates transport proteins
P
Glu +
NH2
NH3
Reactants: Glutamic acid
and ammonia
Figure 8.11
+
Glu
P
i
Product (glutamine)
made
(c) Chemical work: ATP phosphorylates key reactants
i
i
The Structure and Hydrolysis of
ATP
Energy COUPLING by Phosphate Transfer
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
Figure 8.12
Energy from catabolism
(exergonic, energy yielding
processes)
ADP +
P
i
Energy for cellular work
(endergonic, energyconsuming processes)
An active cell needs millions of
molecules of ATP per second
to drive its biochemical
machinery. They’re consumed
in less than a second and an
average person produces and
hydrolyzes about 40 kg of ATP
per day!
•
Enzymes speed up
metabolic reactions by
lowering energy barriers
Enzymes
1.Proteins: most enzymes are
catalytic proteins, primarily
tertiary and quaternary
structures.
2.Catalysts:chemical agents that
accelerate a reaction without
being permanently changed in
the process.
Example of an Enzyme-Catalyzed
Reaction: Hydrolysis of Sucrose
How Do Reactions Occur?
• Spontaneous reactions may
occur very slowly.
• All reactions require free energy
of activation (EA)
• Uphill portion represents the EA
required to start the reaction.
• Downhill portion represents the
loss of free energy by the
molecules in the reaction.
Is this reaction exergonic or endergonic?
How can the EA barrier be
overcome?
• Temperature
• Temperatures that are too high
denature organic molecules, so
what else is there?
• Enzymes lower the EA barrier so that
reactions can occur at lower
temperatures.
Enzymes
Without Enzyme
With Enzyme
Free
Energy
Free energy of activation
Reactants
Products
Progress of the reaction
Enzyme / Substrate
Relationship:
• What is the substrate?
• It is the reactant upon which an
enzyme reacts.
• Enzymes are substrate specific.
• Only the active site of the enzyme
actually binds the substrate.
Substrate
• The substance (reactant) an
enzyme acts on.
Enzyme
Substrate
Active Site
• A restricted region of an
enzyme molecule which
binds to the substrate.
Substrate
Enzyme
Active Site
Enzyme Animations
http://www.biologyalive.com/life/classes/apbiology/
documents/Unit%203/media5/micro_enzymesubstrate.swf
http://www.wiley.com/college/test/0471787159/biolo
gy_basics/animations/howEnzymesWork.html
http://www.cengage.com/biology/discipline_content
/animations/enzyme_role_m.html
http://bcs.whfreeman.com/webpub/Ektron/pol1e/Ani
mated%20Tutorials/at0302/at_0302_enzyme_catalys
is.html
The Active Site
• Most enzyme-substrate
interactions are the result of
weak bonds.
• The active site may cause the
enzyme to hold onto the
substrate in a very specific way.
• The active site may provide a
micro-environment (e.g. low pH)
which enhances a reaction.
Induced Fit
• A change in the configuration of an
enzyme’s active site (H and ionic
bonds are involved).
• Induced by the substrate.
Active Site
substrate
Enzyme
induced fit
Enzymatic Reaction
substrate (sucrose) + enzyme (sucrase) 
enzyme-substrate complex 
products
and
glucose
+ enzyme
+
fructose
sucrase
Enzyme Activity is Affected by:
• Temperature
• pH
• Enzyme
Concentration
• Substrate
Concentration
Cofactors and Coenzymes
• Inorganic substances (zinc, iron)
and vitamins (respectively) are
sometimes needed for proper
enzymatic activity.
• Example:
Iron must be present in the
quaternary structure - hemoglobin in
order for it to pick up oxygen.
Enzyme Inhibitors
• Two examples:
a. Competitive Inhibitors: are
chemicals that resemble an
enzyme’s normal substrate and
compete with it for the active site.
Substrate
Competitive
inhibitor
Enzyme
Enzyme Inhibitors
b.
Noncompetitive Inhibitors:
Inhibitors that do not enter the active
site, but bind to another part of the
enzyme causing the enzyme to
change its shape, which in turn
alters the active site.
Substrate
Enzyme
active site
altered
Noncompetitive
Inhibitor
Allosteric Regulation
• Regulatory molecules that bind to
the enzyme’s allosteric site
changing the shape of the enzyme.
• Allosterically regulated enzymes
have a quaternary protein structure.
• Each subunit of the enzyme has an
active site and an allosteric site.
• Allosteric activators stabilize the
active site
• Allosteric inhibitors deactivate the
active site.
Feedback
Inhibition
A metabolic
pathway is
switched off
by the inhibitory
binding of its end
product to an enzyme
earlier in the pathway
1) In the amylase lab, the
amylase broke down the polysaccharides (starches) into _______.
2) Enzymes work by lowering
the ___________ _________
required for a reaction to occur.