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Cell Energetics 1
What is energy?
Energy
Energy is the ability to do work.
Energy is a phenomenon, not a material.
Two broad categories of energy:
Potential
Kinetic
Potential Energy
Potential energy is stored energy.
Examples: coiled spring, bonds between atoms
Kinetic Energy
Kinetic energy is
energy that has
been released to
do work.
Examples: car in
motion, heat,
light.
Examples of Energy
Potential
Kinetic
Magnetic
Radiant (Light)
Gravity
Electrical
Chemical
Sound
Nuclear
Motion
Stored mechanical
Thermal (heat)
First Law of Thermodynamics
Assuming there is no input of energy, the
total energy within a given system remains
constant. Energy is conserved.
Energy can change form (example:
chemical energy in cells may be converted
to heat, motion, etc.)
Energy Transformations
Potential
Kinetic
Chemical: Energy stored in
Motion: Muscles in motion
chemical bonds in food.
Chemical: Energy stored by
Radiant: Sunlight
photosynthesis.
Electrical: Current used by an Thermal: Heat produced by the
electric heater.
heater.
Motion: Car powered by
Chemical: Gasoline
burning gasoline.
Second Law of Thermodynamics
Assuming there is no input of energy
(closed system), when energy is converted
from one form to another, the amount of
useful energy in the system decreases.
Entropy is the tendency toward an increase
in randomness and disorder in a closed
system.
Thinking Question
Write out an answer to this question:
Do living systems violate the second
law of thermodynamics? Why or why
not?
Share your response with a partner and
discuss what you have written.
Exergonic Reactions
Exergonic (exothermic)
reactions release energy.
In exergonic reactions, the
reactants have more energy
than the products.
However, all chemical
reactions require an input of
energy to get them started.
Exergonic Reaction
Exergonic Reactions: Living systems
In living systems, exergonic reactions are
carried out by enzymes.
Enzymes lower the activation energy
required to get these reactions started, so
there is more net energy at the end.
Enzymes also control the rate of the
reaction so that heat is controlled.
Endergonic Reactions
Endergonic (endothermic)
reactions require an input of
energy.
Products of the reactions
have more energy than the
reactants.
Endergonic Reaction
Ammonium thiocyanate + Barium hydroxide
Coupled Reactions
Living organisms use energy from
exergonic reactions to drive endergonic
reactions.
The reactions may occur in different
places. Energy may be transferred by
energy-carrier molecules such as ATP.
ATP
Adenosine triphosphate
(ATP) is the universal
energy molecule.
ATP is made up of
adenine, a ribose sugar,
and three phosphate
groups.
ATP and Energy
ATP is synthesized from ADP (Adenosine
diphosphate) and a phosphate group, using
energy released from the breakdown of
glucose, fats, and amino acids.
When the terminal phosphate bond in ATP
is broken, energy is released.
ATP is a very unstable molecule.
ATP and Living Organisms
ATP is used by all living organisms.
In plants, the chloroplasts harvest light
to make ATP and use it to make glucose
and other carbon compounds.
Plants, animals, and all other
eukaryotes break down glucose and
other compounds to make ATP for their
metabolic needs.
Thinking Question
Think about all the things going on in your
cells right now.
List as many things as you can think of
that probably require ATP to run them.