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Marvelous Metabolism
Chapter 8
I. Vivacious Vocabulary
Metabolism - total of all an organisms
chemical processes (all the reactions
happening in an organism)
Catabolic pathways - release energy by
breaking down complex molecules into
simpler ones
ex. - respiration
Anabolic pathways - consume energy to
build complex molecules from simpler
ones
ex. - building proteins from amino acids
Bioenergetics - study of how organisms
II. Energy
Capacity to do work
A. Kinetic energy
Energy of motion
Ex.
– Water through dam
– Light powering photosynthesis
– Heat is kinetic energy associated with
RANDOM movement of atoms.
B. Potential energy
Stored energy due to location or structure
Ex.
– Water behind dam (before it’s released)
– Chemical energy - stored in
molecules due to arrangement of
atoms
Organisms are energy transformers!!
III. Thermodynamics
Study of energy transformations
III. Thermodynamics
A. First Law of Thermodynamics - energy
can not be created or destroyed, but it can
be transferred
B. Second Law of Thermodynamics Every energy transfer increases the
entropy (disorder/ randomness) of the
universe
– 1. In most energy transformations, part of the
energy is lost as heat (heat is energy in it’s
most random state)
– 2. Entropy of a system can decrease, as long as
the entropy of the universe (system+
surroundings) increases
IV. Free Energy
Portion of a system’s energy that can
perform work when temperature is
uniform throughout the system
DG = DH - T DS
 DG = change in free energy
 DH = change in system total energy
T = absolute temp (in Kelvin oC + 273)
DS = change in entropy
IV. Free Energy
In any spontaneous process, the free
energy of a system decreases
(DG must be negative)
For a reaction at equilibrium, DG = 0
A. Exergonic reaction
Energy Out
- occur with a release of free energy
-DG = spontaneous reaction
ex. - Cellular respiration
C6H12O6 + 6O2 ---->6CO2 + 6H2O
DG = -686 kcal/mole
B. Endergonic reaction
Energy In
- absorbs free energy from it’s
surroundings
+ DG = nonspontaneous reaction
ex - Photosynthesis
DG = +686 kcal/mole
This reaction is powered by light
energy from the sun
C. Metabolic Disequilibrium
If a cell were allowed to reach
chemical equilibrium, DG = 0, the
cell would be dead. To keep this
from happening, the product of one
reaction becomes a reactant for
another reaction. This keeps
products from building up and
prevents the cell from reaching
equilibrium.
V. Awesome ATP
A. Types of Work - cells do three types
of work
1. Mechanical - muscle contraction,
movement of chromosomes
2. Transport - pumping across
membranes
3. Chemical - pushing endergonic
reactions that would not occur
spontaneously
V. Awesome ATP
B. ATP - source of energy that powers
cellular work
Adenosine triphosphate (adenine +
ribose + 3 phosphate)
1. Bonds between phosphate groups
can be broken by hydrolysis. This
releases energy DG = -7.3 kcal/mol
ATP + H2O ----> ADP + Pi
V. Awesome ATP
2. When ATP is hydrolyzed (broken
down), it can be used to drive
endergonic reactions by
transferring the Pi (phosphate)
group to some other molecule. This
is called Phosphorylation.
V. Awesome ATP
3. ATP can also be regenerated by
adding a Pi to ADP.
This is an endergonic reaction.
DG = +7.3 kcal/mol
This reaction happens continuously
in a cell and is driven by breaking
down glucose in respiration.
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Exciting and
Energetic
Enzymes!!!
I. What are Enzymes?
Enzymes are protein catalysts!!
Catalysts speed up the rate of a
reaction without being consumed!
II. Remember Free Energy?
Activation Energy EA
– Free Energy needed to start a reaction
– Required to break bonds of reactants
– Heat works! It speeds up the molecules,
which collide more and stronger
III. How do Enzymes Work?
Heat doesn’t work for cells because it
denatures proteins...so...Go Enzymes!
Enzymes lower EA barrier so transition
state can be reached at room temperature
Only can speed up reactions that would
occur anyway
Enzymes work on a specific substrate or
reactant
III. How do Enzymes Work?
Enzyme
Substrate ---------------- > Product(s)
Sucrase
Sucrose + H20 ------------- > Glucose + Fructose
Enzymes are so specific, can distinguish
between isomers
Enzymes usually end in -ase
Figure 6.11 Example of an enzyme-catalyzed reaction: Hydrolysis of sucrose
IV. The Detail and the Visual
Enzymes have active sites where the
substrate fits!
When substrate enters the active
site, it induces the enzyme to change
shape slightly so it’s nice and snug.
This is an induced fit. (Big H-bond
Hug!)
About 1000 substrate
molecules/second or more
Figure 6.14 The induced fit between an enzyme and its substrate
V. How do enzymes do these
cool things?
Can stress or twist bonds to induce a break! (less
heat will be required)
Active site may give a micro environment
– Lower pH
– Brief covalent bonds with side chains of the enzyme
The more substrate, the faster the reaction
occurs until the saturation point where enough
to fill each enzyme (vmax)
Sometimes Cofactors (coenzymes) required
-non-protein helpers, vitamins, minerals
VI. Environment can change
A LOT!
Enzymes have an optimal
temperature and pH
Temperature increases the speed of
reactions with enzymes....the
molecules move faster
Too high a temp and the protein
enzymes denature and don’t work 
VII. Evil Enzyme Inhibitors
Competitive Inhibitors:
– Mimic the normal substrate and compete for
admission into active site.
Non-competitive Inhibitor
– Bind to enzyme somewhere other than active
site, change shape of enzyme so substrate
doesn’t fit.
Bad inhibitors include...DDT (pesticides)
and Antibiotics (inhibit bacteria)
VIII. Regulators
Enzymes often have regulator molecules!
These bond to an allosteric site (away
from active site)
Enzyme has two shapes...1 active and 1
inactive
Activators bind to allosteric site and
stabilize the active shape
Inhibitors bind to allosteric site and
causes enzymes inactive shape
VIII. Regulators
Feedback Inhibition
– Metabolic path is shut off because the
end-product acts as an inhibitor by
allosterically binding
– This prevents wasting resources when
there is enough product
IX. Order! Order!
It’s not just random soup out there in cell
land!
Enzyme teams hang out together in a
multienzyme complex
Some enzymes are in fixed locations in the
cell as fixtures in membranes
Some are in solution inside organelles
– Respiration enzymes are in Mighty
Mitochondria
Emergent Properties Rule!!