Slide 1 / 64
Chapter 8
Metabolism
Metabolic Pathways
Slide 2 / 64
Metabolism is the totality of an organism’s chemical reactions.
Metabolism is a property of all life.
Metabolic Pathways
There are two types of metabolic pathways:
Catabolic pathways release energy by breaking down complex
molecules into simpler compounds.
Anabolic pathways consume energy to build complex
molecules from simpler ones.
Slide 3 / 64
Slide 4 / 64
Metabolic Pathways
A metabolic pathway begins with a specific molecule and
ends with a product
Each step is catalyzed by a specific enzyme
No enzyme, no reaction
A
enzyme 3
enzyme 2
enzyme 1
B
Reaction 1
Reaction 2
C
Reaction 3
Starting
Molecule
D
Product
Slide 5 / 64
Biological Energy Flow
Living things use anabolic pathways to synthesize more
complex organic molecules using the energy derived from
catabolic pathways.
Molecules from the environment are broken down.
Their energy and matter are used to:
· build structures
· drive processes
But living things still obey the Laws of Thermodynamics.
The First Law of Thermodynamics
ΔE = w + q
Energy is neither created nor destroyed.
The total energy of the universe is a constant; if a system
loses energy, it must be gained by the surroundings, and
vice versa.
Final
state
E Initial
EFinal < Einitial
∆E < 0 ( negative)
Final
state
E of system decreases
Energy lost to
surroundings
E Final
Internal energy, E
Internal energy, E
Initial
state
E final
E final > E initial
# E > 0 (positive)
Initial
state
E of system increases
Energy gained
from surroundings
E initial
Slide 6 / 64
System and Surroundings
Slide 7 / 64
The system includes whatever we want to study, living
or non-living.
The surroundings are everything else.
Surroundings
System I
System II
Exchange of Heat between
System and Surroundings
When heat is absorbed by
the system, the process is
endothermic.
Slide 8 / 64
When heat is released by
the system, the process
is exothermic.
System
System
Heat
Surroundings
Heat
Endothermic
Exothermic
Remember that a change in heat is
a change of enthalpy.
1
If a hot rock is placed in cold water, and your system is the rock,
the process is _____.
A
endothermic
B
exothermic
C
neither, there is no change in energy
D
it depends on the temperature
Slide 9 / 64
2
3
4
If a hot rock is placed in cold water, and your system is the
water, the process is _____.
A
endothermic
B
exothermic
C
neither, there is no change in energy
D
it depends on the temperature
If an ice cube is placed in warm water, and your system is the
ice cube, the process is _____.
A
endothermic
B
exothermic
C
neither, there is no change in energy
D
it depends on the temperature
If an ice cube is placed in warm water, and your system is the
warm water, the process is _____.
A
endothermic
B
exothermic
C
neither, there is no change in energy
D
it depends on the temperature
Slide 10 / 64
Slide 11 / 64
Slide 12 / 64
5
Water droplets evaporating from the skin surface will make you
feel cold. For your skin, this process is _____.
A
endothermic
B
expothermic
C
neither, there is no change in energy
D
it depends on the temperature
Biological Order and Disorder
Slide 13 / 64
Slide 14 / 64
Life creates ordered structures from less ordered materials in
anabolic reactions.
Life also consumes ordered forms of matter and breaks them
down, releasing energy, with catabolic reactions.
Living things are highly ordered.
Biological Order and Disorder
Organisms increase the disorder of the universe in order to
increase their own order.
Entropy may decrease in an organism, but the universe’s total
entropy increases.
Life obeys the Second Law of Thermodynamics.
Slide 15 / 64
The Second Law of Thermodynamics
Slide 16 / 64
The First Law tells us that energy cannot be created nor
destroyed; the total energy of the universe is a constant.
The First Law allows any process in which the total
energy is conserved, including those where energy
changes forms.
However, the First Law alone cannot explain what we see
around us every day.
The Second Law of Thermodynamics
Slide 17 / 64
For instance, the First Law would allow the broken cup shown
below to reassemble itself, but it never will.
The absence of processes like this shows that the conservation of
energy is not the whole story.
If it were, movies run backwards would look perfectly normal to us!
The Second Law of Thermodynamics
The Second Law is a statement about which processes occur
and which do not.
· Heat can flow spontaneously from a hot object to a cold
object; but not from a cold object to a hot object.
· It is impossible to build a perpetual motion machine.
· The universe always gets more disordered with time.
· Your bedroom will get increasingly messy unless you keep
cleaning it up.
Slide 18 / 64
Order to Disorder
Slide 19 / 64
Natural processes tend to move toward a state of
greater disorder.
· Stir sugar into coffee and you get coffee that is uniformly
sweet. No amount of stirring will get the sugar back out.
· When a tornado hits a building, there is major damage.
You never see a tornado pass through a pile of rubble and
leave a building behind.
· You never walk past a lake on a summer day and see a
puff of steam rise up, leaving a frozen lake behind.
The First Law says all these could happen,
the Second Law says they won't.
Slide 20 / 64
Spontaneous Processes and the
Second Law
The Second Law tell us what will happen spontaneously,
without outside intervention.
Spontaneous doesn't mean fast, it just means that it will
naturally occur if a system is left on its own.
Spontaneous Processes
· Spontaneous processes are those
that can proceed without any
outside intervention.
· The gas in vessel B will
spontaneously effuse into vessel A,
but once the gas is in both vessels,
it will not spontaneously return to
vessel B.
Slide 21 / 64
Spontaneous Processes
Slide 22 / 64
Processes that are spontaneous in
one direction are nonspontaneous in
the reverse direction.
Spontaneous Processes
Slide 23 / 64
· Processes that are spontaneous at one temperature may be
nonspontaneous at other temperatures.
· Above 0 °C it is spontaneous for ice to melt.
· Below 0 °C the reverse process is spontaneous.
6
A reaction that is spontaneous _____.
A
is very rapid
B
will proceed without outsode intervention
C
is also spontaneous in the reverse direction
D
has an equilibrium position that lies far to the left
E
is very slow
Slide 24 / 64
7
Which of the following statements is true?
A
Processes that are spontaneous in one direction are
spontaneous in the opposite direction.
B
Processes are spontaneous because they occur at an
observable rate.
C
Spontaneity can depend on the temperature.
D
All of the above statements are true.
Entropy
Slide 25 / 64
Slide 26 / 64
Entropy is a measure of the randomness or disorder of a system.
The second law of thermodynamics states that the entropy of the
universe increases for spontaneous processes.
8
The thermodynamic quantity that expresses the degree of
disorder in a system is ______.
A
enthalpy
B
internal energy
C
bond energy
D
entropy
E
heat flow
Slide 27 / 64
9
The entropy of the universe is __________.
A
constant
B
continually decreasing
C
continually increasing
D
zero
E
the same as the energy, E
Entropy and Life
Slide 28 / 64
Slide 29 / 64
Growth of an individual, and evolution of a species, are
both processes of increasing order.
Do they violate the second law of thermodynamics?
Entropy and Life
Do they violate the second law of thermodynamics?
No! Life is not an isolated system.
Even though life itself shows increasing order, it creates an
increasing amount of disorder in its surroundings: the total
disorder of the universe is increased by life.
Slide 30 / 64
10 If the entropy of a living organism is decreasing, which of the
following is most likely to be occurring simultaneously?
A
The entropy of the organism's environment must also be
decreasing.
B
Heat is being used by the organism as a source of energy.
C
Energy input into the organism must be occuring in order to
drive the decrease in entropy.
D
In this situation, the second law of thermodynamics must not
apply.
11 According to the second law of thermodynamics, which of the
following is true?
A
Energy conversions increase the order in the universe.
B
The total amount of energy in the universe is constant.
C
The decrease in entropy in life must be offset by an increase
in entropy in the environment.
D
The entropy of the universe is constantly decreasing.
Spontaneous Reactions
Biologists want to know which reactions occur spontaneously
and which require the input of energy.
To do so, they need to determine the energy and entropy
changes that must occur.
As you learned last year, this determines the change in the
Gibbs Free Energy: ΔG.
Slide 31 / 64
Slide 32 / 64
Slide 33 / 64
Spontaneous Processes
Slide 34 / 64
A process will occur spontaneously if the result is a reduction of
the Gibbs Free Energy (G) of the system.
G takes into account the resulting change in the energy of a
system and the change in its entropy.
If the effect of a reaction is to reduce G, the process will proceed
spontaneously.
If ∆G is negative, the reaction will occur spontaneously.
If ∆G is zero or positive, it will not occur spontaneously.
Free-Energy Change: ΔG
Slide 35 / 64
Exergonic reactions have a negative ∆G
and occur spontaneously
Endergonic reactions have a positive ∆G
and do not occur spontaneously
Slide 36 / 64
Spontaneous (Exergonic) Processes
Slide 37 / 64
Exergonic Reaction
Amount of
free
energy
released
(ΔG < 0)
Free energy
Reactants
Energy
Products
Progress of the reaction
Slide 38 / 64
Endergonic Reaction
Free energy
Products
Energy
Amount of
free energy
required
(ΔG > 0)
Reactants
Progress of the reaction
12 A spontaneous reaction _____.
A occurs only when an enzyme or other catalyst is present
B cannot occur outside of a living cell
C
releases free energy when proceeding in the forward direction
D
is common in anabolic pathways
E leads to a decrease in the entropy of the universe
Slide 39 / 64
Free Energy and Metabolism
Slide 40 / 64
The concept of free energy applies to life:
Processes in living systems that lower the Gibbs
free energy are spontaneous; they are exergonic.
Processes that raise the Gibbs free energy are
nonspontaneous; they are endergonic.
Free Energy and Metabolism
Slide 41 / 64
Biological systems often need an endergonic reaction to
occur; on it's own, it won't proceed spontaneously.
But if it is coupled to a reaction that is exergonic, so that
together, they are exergonic, it will take place.
Slide 42 / 64
Coupled Reactions
Non-spontaneous reaction: # G is positive
Glu
Glutamic
acid
NH2
+
# G = +3.4 kcal/mol
NH3
Glu
Ammonia
Spontaneous Reaction:ΔG is negative
ATP
+
H 2O
ΔG = -7.3 kcal/mol
ADP
+
Pi
Slide 43 / 64
Adding Coupled Reactions
Non-spontaneous reaction: # G is positive
NH2
+
Glu
Glutamic
acid
# G = +3.4 kcal/mol
NH3
Glu
Ammonia
Spontaneous Reaction:ΔG is negative
ATP
+
H 2O
together, reactions are
spontaneous
ΔG = -7.3 kcal/mol
ADP
+
Pi
# G = –3.9 kcal/mol
13 Which of the following correctly states the relationship
between anabolic and catabolic pathways?
A
Degradation of organic molecules by anabolic pathways
provides the energy to drive catabolic pathways.
B
Energy derived from catabolic pathways is used to drive the
breakdown of organis molecules in anabolic pathways.
C
Anabolic pathways synthesize more complex organic
molecules using the energy derived from catabolic pathways.
Free Energy and Metabolism
A cell does three main kinds of work:
· Mechanical (motion)
· Transport (crossing a barrier)
· Chemical (changing a molecule)
To do work, cells manage energy resources by energy coupling,
using an exergonic reaction to drive an endergonic one
NOTE: both processes don't have to occur at the same time, it's
possible to store the energy from an exergonic process to drive
an endergonic process at a later time.
Slide 44 / 64
Slide 45 / 64
ATP
Slide 46 / 64
ATP (adenosine triphosphate) is the currency of energy in living
systems.
It stores the energy gained in exergonic reactions to power
endergonic reactions at a later time.
ATP provides the energy for the processes of life.
ATP
Slide 47 / 64
ATP (adenosine triphosphate)
includes three phosphate
groups (PO4-3).
Each Phosphate group has an
ionic charge of -3e.
In this space filling model of
ATP, each PO4-3 is circled in
blue.
ATP
The phosphate groups repel each
other, since they each have a
negative charge.
Therefore it requires Work to add
the second phosphate group; to
go from AMP (monophosphate) to
ADP (diphosphate).
To add the third group, to go from
ADP to ATP (triphosphate),
requires even more work since it
is repelled by both of the other
phosphate groups.
Slide 48 / 64
ATP
Slide 49 / 64
This is like the work in
compressing a spring.
The energy from the work needed
to bring each phosphate group to
the molecule is stored in that
phosphate bond.
When the bond is broken to go
from ATP to ADP, significant
energy is released.
Going from ADP to AMP releases
less energy, since there is less
total charge in ADP than ATP.
ATP
Slide 50 / 64
The bonds between the phosphate groups of ATP’s tail can
be broken by hydrolysis.
Energy is released from ATP when the terminal phosphate
bond is broken.
The released energy is equal to the work that was done to
form the bond. That work overcame the electrostatic
repulsion between the last phosphate group and the initial
ADP molecule.
The result is a chemical change to a state of lower free
energy.
ATP
In the living systems, the energy from the exergonic reaction
of ATP hydrolysis can be used to drive an endergonic
reaction.
Overall, the coupled reactions are exergonic.
Slide 51 / 64
Slide 52 / 64
ATP Performs Work
ATP drives endergonic reactions by phosphorylation,
transferring a phosphate group to some other molecule, such
as a reactant.
The recipient molecule is now "phosphorylated".
The three types of cellular work are powered by the hydrolysis
of ATP.
Slide 53 / 64
ATP Performs
Work
Pi
P
Motor protein
Protein moved
Mechanical work: ATP
phosphorylates motor proteins
Membrane
protein
ADP
ATP
P
Pi
+
Pi
Solute transported
Solute
Transport work: ATP phosphorylates transport proteins
P
Glu +
NH2
NH3
Reactants: Glutamic acid
and ammonia
Glu
+ Pi
Product (glutamine)
made
Chemical work: ATP phosphorylates key reactants
The Regeneration of ATP
ATP is a renewable resource that is regenerated by addition
of a phosphate group to ADP
The energy to phosphorylate ADP comes from catabolic
reactions in the cell
The chemical potential energy temporarily stored in ATP
drives most cellular work
Each cell is converting millions of ATP to ADP and back
again every second.
Slide 54 / 64
The Regeneration of ATP
Slide 55 / 64
ATP
Energy from catabolism
(energonic,
exergonic energyyielding processes)
ADP + P
i
Energy for cellular work
(endergonic, energyconsuming processes)
14 In general, the hydrolysis of ATP drives cellular work by _____.
A
changing to ADP and phosphate
B
releasing free energy that can be coupled to other reactions
C
releasing heat
D
acting as a catalyst
E
lowering the free energy of the reaction
15 What best characterizes the role of ATP in cellular metabolism?
A
The releasse of free energy during the hydrolysis of ATP
heats the surrounding environment.
B
The free energy releasedby ATP hydrolysis may be coupled
to an endergonic process via the formation of a
phosphorylated intermediate.
C
It is catabolized to carbon dioxide and water.
D
The ΔG associated with its hydrolysis is positive.
Slide 56 / 64
Slide 57 / 64
16 Which of the following is not an example of the cellular work
accomplished with the free energy derived from the hydrolysis
of ATP?
A
Mechanical work, such as the moving of flagella.
B
Transport work, such as the active transport of an ion into a
cell.
C
Chemical work, such as the synthesis of new proteins.
D
The production of heat, which raises the temperature of the
cell.
E
All of the above.
Equilibrium and Metabolism
Slide 58 / 64
Slide 59 / 64
Reactions in a closed system eventually reach equilibrium
and then stop.
Life is not in equilibrium
Life is an open system, experiencing a constant flow of
materials and energy.
Life cannot survive without connection to the environment.
Slide 60 / 64
Equilibrium and Metabolism
#G<0
A closed hydroelectric system
#G=0
Equilibrium and Metabolism
Slide 61 / 64
An open hydroelectric system
Equilibrium and Metabolism
#G<0
Slide 62 / 64
#G<0
#G<0
A multistep open hydroelectric system
Equilibrium and Metabolism
The multistep, open hydroelectric system is like life.
Materials being used must be replaced in order for energy to be
produced and work to be done.
Remember... Life is not in equilibrium
Life is an open system experiencing a constant flow of materials and
energy.
Slide 63 / 64
17 Organisms are described as thermodynamically open systems.
Which of the following statements is consistent with this
description?
A
The metabolism of an organism is isolated from its
surroundings.
B
Organisms aquire energy from their surroundings.
C
Heat produced by the organism is conserved in the organism
and not lost to the environment.
D
Because energy must be conserved, organisms constantly
recycle energy and thus need no input of energy.
Slide 64 / 64