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Free Energy
All living systems require constant input of free energy
Metabolism
• Metabolism: the sum total of all the chemical reaction that take place to build up and break down the
materials needed in an organism
• Catabolism: the breaking down of complex molecules
• Exergonic: aka Spontaneous – happens on its own w/o energy
• Releases energy to surroundings/products are more stable than reactants
• ∆G = • Increases disorder (more entropy)
• Anabolism: building complex complex molecules
• Endergonic: aka Nonspontaneous – requires energy to take place
• Stores or absorbs energy from surroundings/products are less stable than reactants
• ∆G = +
• Decreases Disorder (less entropy)
• Metabolic pathways: begin with specific molecule, altered in a series of defined steps, resulting in
certain products
Enzyme 1
A
Starting
molecule
Reaction 1
Enzyme 2
B
Reaction 2
Enzyme 3
C
Reaction 3
D
Product
Free energy
Reactants
Energy
Products
Amount of
energy
released
(∆G < 0)
Progress of the reaction
(a) Exergonic reaction: energy released
Free energy
Products
Energy
Reactants
Amount of
energy
required
(∆G > 0)
Progress of the reaction
(b) Endergonic reaction: energy required
Fig. 8-6a
Free energy
Reactants
Amount of
energy
released
(∆G < 0)
Energy
Products
Progress of the reaction
(a) Exergonic reaction: energy released
Fig. 8-6b
Free energy
Products
Amount of
energy
required
(∆G > 0)
Energy
Reactants
Progress of the reaction
(b) Endergonic reaction: energy required
Forms of Energy
• Kinetic Energy: motions – can do work by transferring motion to other matter (ex: pool
stick – ball to ball)
• Thermal energy: type of kinetic energy; aka heat; random movement of atoms or
molecules
• Anytime bonds are broken there is a transfer of energy from the molecule to
thermal energy (called heat – this is why we say heat is released to the
environment through the food chain – when glucose is broken down in the
presences of oxygen bonds are broken some of the energy stored in the bonds of
the glucose molecule becomes thermal energy  this thermal energy is either lost
to the environment OR if the organisms is an endotherm (relies on internal
temperature control vs external (ectotherm)) the heat is used to maintain the
organisms temperature (called thermoregulation)
• Potential Energy: energy matter posses because its location or structure
• Chemical energy: potential energy available for release in a chemical reaction
A diver has more potential
energy on the platform
than in the water.
Climbing up converts the kinetic
energy of muscle movement
to potential energy.
Diving converts
potential energy to
kinetic energy.
A diver has less potential
energy in the water
than on the platform.
Application
Describe the forms of
energy found in an
apple as it grows on a
tree, then falls and is
digested by someone
who eats it.
Application Answer
• The apple has potential energy in its position hanging
on the tree, and the sugar and other nutrients it
contains have chemical energy. The apple has kinetic
energy as it falls from the tree to the ground. When
the apple is digested and its molecules broken down,
some of the chemical energy is used to do work, and
the rest is lost as thermal energy
• Who knew…so many types of energy in one little
apple!!!
Thermodynamics
• Thermodynamics: study of how energy is transferred (passed along)
or transformed (changed into a different kind of energy)
• System: matter under study
• Universe: everything outside the system
• Isolated system: system unable to exchange either energy or matter
with its surroundings; ex: thermos bottle
• Open system: energy and matter can be exchanged between the
system and its surrounds
Laws of Thermodynamics
• First law: Energy can be transferred and transformed, but it cannot be
created or destroyed; principle of conservation of energy
• Electric Company does not make energy; they convert it to a usable form
• Plants are not actually energy producers, more accurate to call them energy
transformers.
• Second Law: Every energy transfer or transformation increases the
entropy of the universe; for a process to be spontaneous, it must
increase the entropy of the universe
What is Entropy?
• Measure of disorder, or randomness
• The more randomly arrange matter is, the greater its entropy
• Although order can increase locally, the trend towards randomization of the
universe is unstoppable
• As chemical energy in food (C6H12O6) is converted into kinetic energy
(movement) the release of CO2 + H2O + heat is causing the universe to become
more disordered; localized order is increased at the expense of the universe
becoming more disordered
• For a process to occur on its own it must increase the entropy of the universe;
no energy is needed
• If a reaction results in a product that is more ordered than the reactants it is
going to require energy and will not take place on its own…endergonic or
nonspontaneous
Free-Energy Change, ∆G
• The following is an equation that can be used to determine the free energy
available in a chemical reaction:
∆G = ∆H – T∆S
• ∆G = change in free energy; energy available to do work
• ∆H = change in system’s enthalpy (in biological systems = total energy)
• T = absolute temperature in Kelvin (K)
• ∆S = change in entropy; order of the system
• If ∆G = -- then the reaction will be spontaneous and occur without energy; if
∆G = + then the reaction will be nonspontaneous and will require energy
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the system
decreases (∆G < 0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion
(b) Diffusion
(c) Chemical reaction
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneous change
• The free energy of the system
decreases (∆G < 0)
• The system becomes more
stable
• The released free energy can
be harnessed to do work
• Less free energy (lower G)
• More stable
• Less work capacity
• ∆G can be negative only when the
process involves a loss of free energy
during the change from initial state to
final state
• Free energy is the measure of a system’s
instability – its tendency to change to a
more stable state
• Unless something prevents matter, it
wants to move to a more stable state
• Free energy (ability to do work) increases
when a reaction is somehow pushed
away from equilibrium
• A process is spontaneous and can
perform work only when it is moving
towards equilibrium
Fig. 8-5b
Spontaneous
change
(a) Gravitational motion
Spontaneous
change
(b) Diffusion
Spontaneous
change
(c) Chemical reaction
Digestion Time/Application
1. Assume temperature and enthalpy do not change…based
on the equation for free energy change, how would
entropy need to change in order for ∆G to be negative?
Would entropy increase or decrease? If entropy increases,
does that mean the reaction causes an increase in disorder
or decrease in disorder?
2. Assume temperature and entropy do not change…based
on the equation for free energy change, how would
enthalpy need to change to cause ∆G to be negative?
Would the reactants or products become more or less
stable?
Digestion Debrieft
1. Increase in entropy (∆S) would lead to a negative ∆G
 reaction would INCREASE in disorder
2. Decrease in enthalpy (∆H) would lead to a negative
∆G  the products would be more stable than the
reactants; the reaction is exergonic (releasing
energy)
Three main kinds of work
• Chemical work: pushing of endergonic reactions,
which would not occur spontaneously, such as the
synthesis of polymers from monomers
• Transport work: pumping of substances across
membranes against the direction of spontaneous
movement
• Mechanical work: movement (contraction of
muscles, beating of cilia, movement of
chromosomes during cell division)
Energy Coupling
• Energy coupling: the use of an exergonic process to dive an
endergonic reaction
• ATP is responsible for most energy coupling in cells
• Structure of ATP (adenosine triphosphate):
• Essential the RNA adenine nucleotide with two additional phosphate groups
Adenine
3 Phosphate groups
Ribose
Is ∆G negative or positive when ATP becomes
ADP?
- Which molecule is
more stable?
- Is there more of less
disorder in ATP or
ADP?
- Is this reaction
endergonic or
exergonic?
- Is this reaction
Pi
spontaneous or non
spontaneous?
P
P
P
Adenosine triphosphate (ATP)
H2O
+
Inorganic phosphate
P
P
+
Adenosine diphosphate (ADP)
Energy
How ATP drives
chemical work
• ATP drives endergonic
reactions by
phosphorylation
(transferring a
phosphate group to
some other molecule)
• The recipient molecule
is now phosphorylated
energy rich and
unstable
• The combined rxns are
exergonic
NH2
NH3
+
Glu
Glutamic
acid
(a) Endergonic
Glu
Ammonia
∆G = +3.4 kcal/mol
Glutamine
reaction
P
1 ATP phosphorylates
glutamic acid,
making the amino
acid less stable.
+
Glu
ATP
Glu
+ ADP
NH2
2 Ammonia displaces
the phosphate group,
forming glutamine.
(b) Coupled
P
Glu
+
NH3
Glu
+ Pi
with ATP hydrolysis, an exergonic reaction
(c) Overall
free-energy change
Membrane protein
How ATP drives
transport and
mechanical work
• The phosphate group
from the ATP binds the
the protein and causes
the shape of the protein to
change
P
Solute
Pi
Solute transported
(a) Transport work: ATP phosphorylates
transport proteins
ADP
+
ATP
Pi
Vesicle
Cytoskeletal track
ATP
Motor protein
Protein moved
(b) Mechanical work: ATP binds noncovalently
to motor proteins, then is hydrolyzed
The Regeneration of ATP
• ATP is a renewable resource that is regenerated by
addition of a phosphate group to adenosine
diphosphate (ADP)
• ADP + P --> ATP
• The energy to phosphorylate ADP comes from catabolic
reactions in the cell.
• The chemical potential energy temporarily stored in ATP
drives most cellular work.
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
The ATP cycle
ATP
Energy from
catabolism (exergonic,
energy-releasing
processes)
+
ADP + Pi
H2O
Energy for cellular
work (endergonic,
energy-consuming
processes)
How much total energy does an organisms
need to stay alive?
• Metabolic rate: amount of energy an animal uses in a unit of time
• Can be determined in several ways:
• Because nearly all of the chemical energy used in cellular respiration eventually appears
as heat, metabolic rate can be measured by monitoring an animal’s rate of heat loss
• Amount of oxygen consumed or carbon dioxide produced
• Record the rate of food consumption, the energy content of the food and chemical
energy lost in waste products
• Amount of energy is going to differ depending on size, shape, and type of
thermoregulation (how an organisms stay warm), age, activity, nutrition,
temperature
• Endotherm: internal
• Ectotherm: external
Size and Metabolic Rate
• In general smaller organisms have a higher
metabolic rate than larger animals; a mouse
needs more energy per unit mass compared to
an elephant. This does not mean the elephant
eats less than the mouse…it means the elephant
needs less energy for every square inch of body
mass compared to the mouse
Activity and Metabolic Rate
• Increased activity = increased need for energy
• Decreased activity = decreased need for energy
• What happens when you have an excess supply of energy?
• Storage – what does this mean???
• What happens when you have a deficient of energy?
• Organism dies
• What impact does this have on the population? Ecosystem?
• Leads to disruptions in ecosystems
• To conserve on energy during times of stress some organisms go into
a Torpor or Hibernation state (long term torpor)