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Cell Energy
Let’s get moving!
Energy

The ability to do work or cause
change! Involves movement!
(Even at the molecular level!)
– Kinetic E (KE): The E that is
actually doing work, i.e. moving
something and transferring that
motion!
• Heat, light, sound
– Potential E (PE): Stored E, the
capacity to perform work due to
location or position
Types of
Cell Work

Chemical: endergonic reactions that would
not occur spontaneously
–

Ex. Synthesis of polymers from monomer
Mechanical: physical motion
– cilia beating, muscle contraction, flow of
cytoplasm

Transport: active transport
– Moving molecules against the concentration
gradient
Thermodynamics
The study of the behavior of
energy flow in natural systems.
Laws of Thermodynamics
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First Law: aka. The Law of Conservation of Energy:
Energy is neither created nor destroyed, energy
can be transformed.
– The energy in the universe is constant.
Second Law: energy conversions reduce the order
of the universe (increasing entropy)
– Heat
– As a particular system becomes more ordered,
its surroundings become more disordered
• A cell is an island of low entropy in an
increasingly random universe!
FYI: Third Law: if all the kinetic energy could be
removed, a state called absolute zero would occur.
Absolute zero results in a temperature of 0 Kelvin
or -273.15° Celsius.
The First Law:
The Transformation of Energy
Energy is conserved.
Conservation of energy
means it can change
forms between kinetic
and potential, but it
never disappears.The
total amount of energy
is always the same.
Transferring Energy in Food
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Food is digested and stored in our bodies as
potential energy.
This potential energy can be transformed into
kinetic energy as our bodies move and exercise.
Chemicals may also be considered from a potential
energy (PE) or kinetic energy (KE) standpoint. One
pound of sugar has a certain PE. If that pound of
sugar is burned the E is released all at once. The E
released is KE (heat). So much is released that
organisms would burn up if all the E was released
at once. Organisms must release the E a little bit
at a time.
When you exercise, you get hot.
What do you think is happening?
A reminder…

Heat cannot be transferred from a
colder to a hotter body. As a result
of this fact of thermodynamics,
natural processes that involve energy
transfer must have one direction, and
all natural processes are irreversible.
The Second Law of Thermodynamics

Second Law: energy conversions
reduce the order of the universe.
– The amount of disorder in a system is
called entropy. (energy lost as heat.)
– As a system becomes more ordered, its
surroundings become more disordered!
• Lots of disorder = high entropy
• Order = low entropy
Moving towards equilibrium

The ultimate result of the Second
Law of Thermodynamics is that
energy in the universe is steadily
deteriorating, or "un-winding", to
lower and lower quality. The universe
is steadily moving toward total
equilibrium
In summary:

In simplest terms, the Laws of
Thermodynamics dictate the specifics
for the movement of heat and work.
– Basically, the First Law of Thermodynamics is
a statement of the conservation of energy –
– the Second Law is a statement about the
direction of that conservation –
– and the Third Law is a statement about
reaching Absolute Zero (0° K).
Thermodynamics is the study of the
inter-relation between heat, work and
internal energy of a system.
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The British scientist and author C.P. Snow had an
excellent way of remembering the three laws:
You cannot win (you cannot get something for
nothing, because matter and energy are
conserved)
You cannot break even (you cannot return to
the same energy state, because there is
always an increase in disorder; entropy
always increases).
You cannot get out of the game (because
absolute zero is unattainable).
Reminder…
Energy associated with reactions
Exergonic Reactions
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Chemical reactions
which involve a net
release of free E.
Ex. Cellular respiration
- the chemical reaction
in which sugars are
broken down to CO2 and
H2O, releasing E.
Requires an initial input
of E to get the reaction
started, called
activation E.
Endergonic Reactions

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Reactions that involve
a net absorption of
free energy.
Ex. photosynthesis the chemical reaction
in which CO2 and
H2O are combined to
make sugars, storing
E E.
Requires an initial
input of E to get the
reaction started,
called activation E.
Metabolism

The sum total
of all the
endergonic
and exergonic
reactions that
take place in a
working cell
and organism.
Energy Coupling
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Using energy released from exergonic
reactions to drive essential endergonic
reactions.
ATP molecules are the essential to
energy coupling in biological systems.
ATP powers nearly all forms of cellular
work.
Enzymes!
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Go back and visit your information on
enzymes!
http://www.indiana.edu/~oso/animations
/An6.html
Cell Energy
ATP: Adenosine triphosphate
ATP: Notice the “~” bonds
ATP Cycle
Phosphorylation

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ATP, the "high-energy" exchange
medium in the cell, is synthesized in the
mitochondrion by addition of a third
phosphate group in a process referred
to as phosphorylation.
ATP is synthesized at the expense of
solar energy by photophosphorylation in
the chloroplasts in the of plant cells.
ATP moves energy around by
phosphorylation.
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Phosphorylation is
the addition of a
phosphate (PO4)
group to a protein
molecule or a small
molecule.
Think “hot potato!”
ATP
How it works…
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ATP works by losing the endmost
phosphate group by hydrolysis when
instructed to do so by an enzyme.
This reaction releases a lot of energy,
which the organism can then use to build
proteins, contact muscles, etc.
The reaction product is adenosine
diphosphate (ADP), and the phosphate
group
– Even more energy can be extracted by
removing a second phosphate group to
produce adenosine monophosphate (AMP).
Con’t…
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When the organism is resting and energy is
not immediately needed, the reverse
reaction takes place and the phosphate
group is reattached to the molecule using
energy obtained from food or sunlight.
Thus the ATP molecule acts as a chemical
'battery', storing energy when it is not
needed, but able to release it instantly
when the organism requires it.
ATP Cycle
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Remember, phosphorylation transfers
energy.
What is ATP synthase (a.k.a. ATP
ase)? What does it do?
What is this energy used for?
How much energy do we use?
Biosynthesis in E. coli modified from
Ensign(1998)
Cell
constituent
DNA
RNA
Polysacchar
ides
Lipids
Proteins
Number of
molecules
per cell
1
15,000
39,000
Molecules of
Molecules
ATP required
synthesized
per second
per second
for synthesis
0.00083
60,000
12.5
75,000
32.5
65,000
15,000,000 12,500.0
1,700,000
1,400.0
87,000
2,120,000