Page 1
.
Chapter 8: Energy and
Metabolism Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:
energy and thermodynamics
metabolic reactions and energy transfers
Harvesting and using energy
ATP is the main energy currency in cells
energy harvesting (redox reactions)
Regulating reactions: Enzymes
Page 2
.
• Discuss energy conversions and the 1st
and 2nd law of thermodynamics.
– Be sure to use the terms
• work
• potential energy
• kinetic energy
• entropy
• What are Joules (J) and calories (cal)?
Page 3
.
Chapter 8: Energy and
Metabolism Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:
energy and thermodynamics
metabolic reactions and energy transfers
Harvesting and using energy
ATP is the main energy currency in cells
energy harvesting (redox reactions)
Regulating reactions: Enzymes
Page 4
.
Energy and Thermodynamics
energy for work: change in state or motion of matter
Page 5
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Energy and Thermodynamics
energy for work: change in state or motion of matter
expressed in Joules or calories
1 kcal = 4.184 kJ
Page 6
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Energy and Thermodynamics
energy for work: change in state or motion of matter
expressed in Joules or calories
1 kcal = 4.184 kJ
energy conversion: energy form change
potential / kinetic
Page 7
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Energy and Thermodynamics potential energy (capacity to
do work)
Page 8
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Energy and Thermodynamics potential energy (capacity to
do work)
kinetic energy (energy of motion, actively performing work)
chemical bonds: potential energy
work is required for the processes of life
Page 9
.
• Discuss energy conversions and the 1st
and 2nd law of thermodynamics.
– Be sure to use the terms
• work
• potential energy
• kinetic energy
• entropy
• What are Joules (J) and calories (cal)?
Page 10
.
Energy and Thermodynamics
Laws of thermodynamics describe the constraints on energy usage…
Page 11
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• The laws of thermodynamics are
sometimes stated as:
– In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
Page 12
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Laws of Thermodynamics
First law:
the total amount of energy (+ matter) in a closed system remains constant
Page 13
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Laws of Thermodynamics
First law:
the total amount of energy (+ matter) in a closed system remains constant
also called conservation of energy
Page 14
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Laws of Thermodynamics
First law:
the total amount of energy (+ matter) in a closed system remains constant
also called conservation of energy
note:
the universe is a closed system
living things are open systems
Page 15
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Laws of Thermodynamics
First law:
the total amount of energy (+ matter) in a closed system remains constant
also called conservation of energy
note:
the universe is a closed system
living things are open systems
“You can’t win.”
Page 16
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Laws of Thermodynamics
Second law: in every energy conversion
some energy is converted to heat energy
heat energy is lost to the surroundings
heat energy cannot be used for work
Page 17
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Laws of Thermodynamics
Second law: in every energy conversion
some energy is converted to heat energy
heat energy is lost to the surroundings
heat energy cannot be used for work
energy converted to heat in the surroundings
increases entropy (spreading of energy)
Page 18
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Laws of Thermodynamics
Second law: in every energy conversion
some energy is converted to heat energy
heat energy is lost to the surroundings
heat energy cannot be used for work
energy converted to heat in the surroundings
increases entropy (spreading of energy)
thus, this law can also be stated as:
Every energy conversion increases the entropy
of the universe.
Page 19
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Laws of Thermodynamics Second law:
Upshot: no energy conversion is 100% efficient
“You can’t break even.”
Just to maintain their current state, organisms must get a constant influx of energy because of energy lost in conversions
Page 20
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• The laws of thermodynamics are
sometimes stated as:
– In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
Page 21
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• Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
Page 22
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Metabolism: anabolism + catabolism
metabolism divided into
anabolism (anabolic reactions)
anabolic reactions are processes that build complex molecules from simpler ones
Page 23
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Metabolism: anabolism + catabolism
metabolism divided into
anabolism (anabolic reactions)
anabolic reactions are processes that build complex molecules from simpler ones
catabolism (catabolic reactions)
catabolic reactions are processes the break down complex molecules into simpler ones
Page 24
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• Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
Page 25
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Chemical Reactions and Free Energy
Chemical reactions involve
changes in chemical bonds
Page 26
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Chemical Reactions and Free Energy
Chemical reactions involve
changes in chemical bonds
changes in substance concentrations
Page 27
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Chemical Reactions and Free Energy
Chemical reactions involve
changes in chemical bonds
changes in substance concentrations
changes in free energy
free energy = energy available to do work in a chemical reaction (such as: create a chemical bond)
free energy changes depend on bond energies and concentrations of reactants and products
bond energy = energy required to break a bond; value depends on the bond
Page 28
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Chemical Reactions and Free Energy
left undisturbed, reactions will reach dynamic equilibrium when the relative concentrations of reactants and products is correct
forward and reverse reaction rates are equal; concentrations remain constant
Page 29
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Chemical Reactions and Free Energy
left undisturbed, reactions will reach dynamic equilibrium when the relative concentrations of reactants and products is correct
forward and reverse reaction rates are equal; concentrations remain constant
cells manipulate relative concentrations in many ways so that equilibrium is rare
Page 30
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Chemical Reactions and Free Energy
exergonic reactions – the products have less free
energy than reactants
the difference in energy is released and is available to do
work
Page 31
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Chemical Reactions and Free Energy exergonic reactions – the products have less free
energy than reactants
the difference in energy is released and is available to do work
exergonic reactions are thermodynamically favored; thus, they are spontaneous, but not necessarily fast (more on activation energy later)
Page 32
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Chemical Reactions and Free Energy
catabolic reactions are usually exergonic
ATP + H2O ADP + Pi is highly exergonic
Page 33
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Chemical Reactions and Free Energy
endergonic reactions – the products have
more free energy than the reactants
the difference in free energy must be supplied
(stored in chemical bonds)
Page 34
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Chemical Reactions and Free Energy
endergonic reactions – the products have more free energy than the reactants
the difference in free energy must be supplied (stored in chemical bonds)
endergonic reactions are not thermodynamically favored, so they are not spontaneous
Page 35
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Chemical Reactions and Free Energy
Page 36
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Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
Page 37
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Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
couple with an exergonic one!
Page 38
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Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
couple with an exergonic one!
together, the coupled reactions must have a net exergonic nature
Page 39
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Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
couple with an exergonic one!
together, the coupled reactions must have a net exergonic nature
reaction coupling requires that the reactions share a common intermediate(s)
Page 40
.
Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Page 41
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Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Coupled: A + C B + D (overall exergonic)
Page 42
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Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Coupled: A + C B + D (overall exergonic)
Actually: A + C I B + D
Page 43
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Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Coupled: A + C B + D (overall exergonic)
Actually: A + C I B + D
typically, the exergonic reaction in the couple is
ATP + H2O ADP + Pi
anabolic reactions are usually endergonic
Page 44
.
Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Coupled: A + C B + D (overall exergonic)
Actually: A + C I B + D
typically, the exergonic reaction in the couple is
ATP + H2O ADP + Pi
anabolic reactions are usually endergonic
This will be explored in more detail in an example in a bit, but first some more about ATP…
Page 45
.
Chapter 8: Energy and
Metabolism Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:
energy and thermodynamics
metabolic reactions and energy transfers
Harvesting and using energy
ATP is the main energy currency in cells
energy harvesting (redox reactions)
Regulating reactions: Enzymes
Page 46
.
Why is ATP so darned important?
What is a phosphorylated intermediate?
How much ATP is in a cell at any given time?
Why must cells keep a high ATP/ADP ratio?
Page 47
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ATP is the main energy currency in cells
One way that organisms manage their energy needs is to use ATP as a ready energy source for many reactions.
Page 48
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ATP is the main energy currency in cells
ATP – nucleotide with adenine base, ribose sugar, and a chain of 3 phosphate groups
Page 49
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ATP is the main energy currency in cells
last two phosphate groups are joined to the chain by unstable bonds; breaking these bonds is relatively easy and releases energy; thus:
Page 50
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ATP is the main energy currency in cells
hydrolysis of ATP to ADP and inorganic phosphate (Pi) releases energy
ATP + H2O ADP + Pi
Page 51
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ATP is the main energy currency in cells
hydrolysis of ATP to ADP and inorganic phosphate (Pi) releases energy
ATP + H2O ADP + Pi
the amount of energy released
depends in part on concentrations of reactants and products
is generally ~30 kJ/mol
Page 52
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ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to a reaction to provide energy
Page 53
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ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to a reaction to provide energy
often phosphorylated compounds
glucose glucose-6-phosphate
Page 54
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ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to a reaction to provide energy
often phosphorylated compounds
the inorganic phosphate is transferred onto another compound rather than being immediately released
glucose glucose-6-phosphate
Page 55
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ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to a reaction to provide energy
often phosphorylated compounds
the inorganic phosphate is transferred onto another compound rather than being immediately released
a phosphorylated compound is in a higher energy state
glucose glucose-6-phosphate
Page 56
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ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP sucrose +ADP + Pi
with intermediates:
glucose + fructose + ATP + H2O glucose-P + fructose + ADP sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)
Page 57
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ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O ADP + Pi (exergonic; provides ~30 kJ/mol)
Page 58
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ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O sucrose + H2O + ADP + Pi
Page 59
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ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP sucrose +ADP + Pi
Page 60
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ATP is the main energy currency in cells
EXAMPLE of a coupled reaction:
glucose + fructose sucrose + H2O (endergonic; requires ~27 kJ/mol)
ATP + H2O ADP + Pi (exergonic; provides ~30 kJ/mol)
coupled:
glucose + fructose + ATP + H2O sucrose + H2O + ADP + Pi
simplified:
glucose + fructose + ATP sucrose +ADP + Pi
with intermediates:
glucose + fructose + ATP + H2O glucose-P + fructose + ADP sucrose + H2O + ADP + Pi (net exergonic, releases ~3 kJ/mol)
Page 61
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ATP is the main energy currency in cells
Thus, energy transfer in cellular reactions is often accomplished through transfer of a phosphate group from ATP
Page 62
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ATP is the main energy currency in cells
Making ATP involves an endergonic condensation reaction
reverse of an exergonic reaction is always endergonic
ADP + Pi ATP + H2O
Page 63
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ATP is the main energy currency in cells
Making ATP involves an endergonic condensation reaction
reverse of an exergonic reaction is always endergonic
ADP + Pi ATP + H2O
endergonic, usually requires more than ~30 kJ/mol
Page 64
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ATP is the main energy currency in cells
Making ATP involves an endergonic condensation reaction
reverse of an exergonic reaction is always endergonic
ADP + Pi ATP + H2O
endergonic, usually requires more than ~30 kJ/mol
must be coupled with an exergonic reaction; typically from a catabolic pathway (more on that later)
Page 65
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ATP is the main energy currency in cells
Overall, ATP is typically created in catabolic reactions and used in anabolic reactions, linking those aspects of metabolism
Page 66
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ATP is the main energy currency in cells
Cells maintain high levels of ATP relative to ADP
maximizes energy available from hydrolysis of ATP
Page 67
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ATP is the main energy currency in cells
Cells maintain high levels of ATP relative to ADP
maximizes energy available from hydrolysis of ATP
ratio typically greater than 10 ATP: 1 ADP
Page 68
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ATP is the main energy currency in cells
Overall concentration of ATP still very low
supply typically only enough for a few seconds at best
Page 69
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ATP is the main energy currency in cells
Overall concentration of ATP still very low
supply typically only enough for a few seconds at best
instability prevents stockpiling
Page 70
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ATP is the main energy currency in cells
Overall concentration of ATP still very low
supply typically only enough for a few seconds at best
instability prevents stockpiling
must be constantly produced
in a typical cell, the rate of use and production of ATP is about 10 million molecules per second
resting human has less than 1 g of ATP at any given time but uses about 45 kg per day
Page 71
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Why is ATP so darned important?
What is a phosphorylated intermediate?
How much ATP is in a cell at any given time?
Why must cells keep a high ATP/ADP ratio?
Page 72
.
• What are redox reactions used for in
cells?
• How (generally) can you tell which of
two similar compounds is reduced and
which is oxidized?
• Give some examples of compounds
commonly used in redox reactions in
cells.
Page 73
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Redox reactions are also used for
energy transfer Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.
Page 74
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Redox reactions are also used for
energy transfer Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.
Electrons can also be used for energy transfer
Page 75
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Redox reactions are also used for
energy transfer Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as
energy currency.
Electrons can also be used for energy transfer
Redox reactions: recall reduction, gain electrons;
oxidation, lose electrons; both occur simultaneously in cells
(generally no free electrons in cells)
Page 76
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Redox reactions are also used for
energy transfer Redox reactions are used to harvest energy from some chemicals.
The acceptors of that energy typically cannot be used directly as energy currency.
Electrons can also be used for energy transfer
Redox reactions: recall reduction, gain electrons; oxidation, lose electrons; both occur simultaneously in cells (generally no free electrons in cells)
Typically, the oxidized substance gives up energy with the electron, the reduced substance gains energy with the electron
Page 77
08.04 Redox Reactions
Slide number: 6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Loss of electron (oxidation)
A*
+ e–
B A B*
_
Gain of electron (reduction)
Low energy
High energy
A B
o o
+
Page 78
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Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common
more on electron transport chains later
Page 79
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Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common
more on electron transport chains later
each electron transfer releases free energy
free energy can be used for other chemical reactions
Page 80
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Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common
more on electron transport chains later
each electron transfer releases free energy
free energy can be used for other chemical reactions
proton often removed as well
if so, equivalent of a hydrogen atom is transferred
Page 81
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Redox reactions are also used for
energy transfer
Catabolism typically involves:
removal of hydrogen atoms from nutrients
(such as carbohydrates)
transfer of the protons and electrons to
intermediate electron acceptors
Page 82
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Redox reactions are also used for
energy transfer intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)
Page 83
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Redox reactions are also used for
energy transfer intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)
Use XH2 to represent a nutrient molecule:
XH2 + NAD+ X + NADH + H+
Page 84
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Redox reactions are also used for
energy transfer intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)
Use XH2 to represent a nutrient molecule:
XH2 + NAD+ X + NADH + H+
Often, the reduced form is just called NADH
Page 85
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Redox reactions are also used for
energy transfer
Reduced state stores energy, which
is partially released as free energy
when NADH is oxidized
Page 86
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Redox reactions are also used for
energy transfer
Reduced state stores energy, which
is partially released as free energy
when NADH is oxidized
The free energy usually winds up
being used to make ATP
Page 87
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Redox reactions are also used for
energy transfer
Other commonly used acceptors are NADP+, FAD, and cytochromes
NADP+/NADPH – important in photosynthesis
FAD/FADH2 – flavin adenine dinucleotide
Cytochromes – small iron-containing proteins; iron serves as electron acceptor
Page 88
.
• What are redox reactions used for in
cells?
• How (generally) can you tell which of
two similar compounds is reduced and
which is oxidized?
• Give some examples of compounds
commonly used in redox reactions in
cells.
Page 89
.
Chapter 8: Energy and
Metabolism Why do organisms need energy? How do organisms
manage their energy needs?
Defining terms and issues:
energy and thermodynamics
metabolic reactions and energy transfers
Harvesting and using energy
ATP is the main energy currency in cells
energy harvesting (redox reactions)
Regulating reactions: Enzymes
Page 90
.
• What do enzymes do for cells, and how
do they do it?
– Be sure to use the following terms:
• catalyst (or catalyze)
• activation energy
• enzyme-substrate complex
• active site
• induced fit
Page 91
.
Enzymes
Manipulation of reactions is essential to and largely defining of life.
Page 92
.
Enzymes
Manipulation of reactions is essential to and largely defining of life.
Organisms use enzymes to manipulate the speed of reactions.
Page 93
.
Enzymes
Manipulation of reactions is essential to and largely defining of life.
Organisms use enzymes to manipulate the speed of reactions.
Understanding life requires understanding how enzymes work.
Page 94
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Enzymes Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst
Page 95
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Enzymes Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst
catalyst –increases the rate of a chemical reaction
without being consumed in the reaction (the catalyst
recycles back to its original state)
Page 96
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Enzymes Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst
catalyst –increases the rate of a chemical reaction
without being consumed in the reaction (the catalyst
recycles back to its original state)
enzymes (catalysts) only alter reaction rate;
thermodynamics still governs whether the reaction
can occur
Page 97
Fig. 8.9 (TEArt)
The substrate, sucrose, consists of glucose and fructose bonded together.
1
The substrate binds to the enzyme, forming an enzyme- substrate complex.
2
The binding of the substrate and enzyme places stress on the glucose- fructose bond, and the bond breaks.
3
Products are released, and the enzyme is free to bind other substrates.
4 Bond
Enzyme
Active site
H2O
Glucose Fructose
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Page 98
08.09 Enzyme Catalytic Cycle
Slide number: 2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Enzyme
Active site
Page 99
08.09 Enzyme Catalytic Cycle
Slide number: 3
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Enzyme
Active site
Page 100
08.09 Enzyme Catalytic Cycle
Slide number: 4
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Enzyme
Active site
The substrate binds to the
enzyme, forming an enzyme-
substrate complex.
2
Page 101
08.09 Enzyme Catalytic Cycle
Slide number: 5
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Enzyme
Active site
The substrate binds to the
enzyme, forming an enzyme-
substrate complex.
2
H2O
The binding of the substrate
and enzyme places stress
on the glucose-fructose
bond, and the bond breaks.
3
Page 102
08.09 Enzyme Catalytic Cycle
Slide number: 6
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
1 The substrate, sucrose, consists
of glucose and fructose bonded
together.
Bond
Enzyme
Active site
The substrate binds to the
enzyme, forming an enzyme-
substrate complex.
2
H2O
The binding of the substrate
and enzyme places stress
on the glucose-fructose
bond, and the bond breaks.
3
Glucose Fructose
Products are
released, and the
enzyme is free to
bind other
substrates.
4
Page 103
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Enzymes work by lowering activation energy of a reaction
all reactions have a required energy of activation
Page 104
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Enzymes work by lowering activation energy of a reaction
all reactions have a required energy of activation
energy required to break existing bonds and bring reactants together
Page 105
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Enzymes work by lowering activation energy of a reaction
all reactions have a required energy of activation
energy required to break existing bonds and bring reactants together
must be supplied in some way before the reaction can proceed
Page 106
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Enzymes
activation energy
catalysts greatly reduce the activation energy
requirement, making it easier for a reaction to occur
Page 107
.
Enzymes Enzymes lower activation energy by forming a complex with the
substrate(s)
the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme
Page 108
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Enzymes Enzymes lower activation energy by forming a complex with the
substrate(s)
the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme
the site where the substrate(s) binds to the enzyme is called the active site
Page 109
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Enzymes Enzymes lower activation energy by forming a complex with the
substrate(s)
the ability to form an enzyme-substrate complex is highly dependent on the shape of the enzyme
the site where the substrate(s) binds to the enzyme is called the active site
when the enzyme-substrate complex forms, there are typically shape changes in the enzyme and substrate(s) – called induced fit
Page 110
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Enzymes
ES complex typically very unstable
Page 111
.
Enzymes
ES complex typically very unstable
short-lived
Page 112
.
Enzymes
ES complex typically very unstable
short-lived
breaks down into released product(s) and a free enzyme that is ready to be reused
Page 113
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Enzymes
ES complex typically very unstable
short-lived
breaks down into released product(s) and a free enzyme that is ready to be reused
overall:
enzyme + substrate(s) ES complex enzyme + product(s)
Page 114
.
• What do enzymes do for cells, and how
do they do it?
– Be sure to use the following terms:
• catalyst (or catalyze)
• activation energy
• enzyme-substrate complex
• active site
• induced fit
Page 115
.
• What are the four main things that
enzymes do to lower activation energy?
Page 116
.
Enzymes reduction in activation energy is due primarily to four things:
Page 117
.
Enzymes reduction in activation energy is due primarily to four things:
an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions
Page 118
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Enzymes reduction in activation energy is due primarily to four things:
an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions
an enzyme may put a “strain” on existing bonds, making them
easier to break
Page 119
.
Enzymes reduction in activation energy is due primarily to four things:
an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions
an enzyme may put a “strain” on existing bonds, making them
easier to break
an enzyme provides a “microenvironment” that is more
chemically suited to the reaction
Page 120
.
Enzymes reduction in activation energy is due primarily to four things:
an enzyme holds reactants (substrates) close together in the
right orientation for the reaction, which reduces the reliance
on random collisions
an enzyme may put a “strain” on existing bonds, making them
easier to break
an enzyme provides a “microenvironment” that is more
chemically suited to the reaction
sometimes the active site of the enzyme itself is directly
involved in the reaction during the transition states
Page 121
.
Enzymes enzyme + substrate(s) ES complex enzyme + product(s)
Page 122
.
• What are the four main things that
enzymes do to lower activation energy?
Page 123
.
• How are enzymes named (what suffixes
indicate an enzyme)?
Page 124
.
Enzymes Enzyme names
many names give some indication of substrate
Page 125
.
Enzymes Enzyme names
many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)
Page 126
.
Enzymes Enzyme names
many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)
some end in –zyme (example: lysozyme)
Page 127
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Enzymes Enzyme names
many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)
some end in –zyme (example: lysozyme)
some traditional names are less indicative of enzyme function (examples: pepsin, trypsin)
Page 128
.
Enzymes
Enzymes are generally highly specific
overall shape as well as spatial arrangements in the active site limit what enzyme-substrate complexes can readily form
Page 129
.
Enzymes
the amount of specificity depends on the particular enzyme
example of high specificity: sucrase splits sucrose, not other disaccharides
Page 130
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Enzymes
the amount of specificity depends on the particular enzyme
example of high specificity: sucrase splits sucrose, not other disaccharides
example of low specificity: lipase splits variety of fatty acids from glycerol
Page 131
.
Enzymes
enzymes are classified by the kind of reaction they catalyze
The International Union of Biochemistry and Molecular Biology has developed a nomenclature for enzymes; the top-level classification is
Oxidoreductases: catalyze oxidation/reduction reactions
Transferases: transfer a functional group (e.g. a methyl or phosphate group)
Hydrolases: catalyze the hydrolysis of various bonds
Lyases: cleave various bonds by means other than hydrolysis and oxidation
Isomerases: catalyze isomerization changes within a single molecule
Ligases: join two molecules with covalent bonds
The complete nomenclature can be browsed at http://www.chem.qmul.ac.uk/iubmb/enzyme/
Page 132
.
• How are enzymes named (what suffixes
indicate an enzyme)?
Page 133
.
• Explain the terms cofactor, apoenzyme,
and coenzyme.
Page 134
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
Page 135
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
apoenzyme + cofactor active enzyme (bound together)
Page 136
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
apoenzyme + cofactor active enzyme (bound together)
alone, an apoenzyme or a cofactor has little if any catalytic activity
Page 137
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
apoenzyme + cofactor active enzyme (bound together)
alone, an apoenzyme or a cofactor has little if any catalytic activity
cofactors may or may not be changed by the reaction
Page 138
.
Enzymes cofactors can be organic or inorganic
organic examples (coenzymes):
ADP, NAD+, NADP+, FAD
typically changed by the catalyzed reaction
Page 139
.
Enzymes cofactors can be organic or inorganic
organic examples (coenzymes):
ADP, NAD+, NADP+, FAD
typically changed by the catalyzed reaction
inorganic examples:
metal ions like Ca2+, Mg2+, Fe3+, etc.
typically not changed by the catalyzed reaction
Page 140
.
Enzymes cofactors can be organic or inorganic
organic examples (coenzymes):
ADP, NAD+, NADP+, FAD
typically changed by the catalyzed reaction
inorganic examples:
metal ions like Ca2+, Mg2+, Fe3+, etc.
typically not changed by the catalyzed reaction
most vitamins are coenzymes or part of coenzymes, or are used for making coenzymes
Page 141
Fig. 8.3 (TEArt)
Product
H
H
H
H
NAD+
NAD
NAD
H
Energy-rich molecule
1. Enzymes that harvest
hydrogen atoms have a
binding site for NAD+
located near another
binding site. NAD+ and
an energy-rich
molecule bind to
the enzyme.
3. NADH then
diffuses away and
is available to
other molecules.
2. In an oxidation-
reduction reaction,
a hydrogen atom
is transferred to
NAD+, forming
NADH.
Enzyme
NAD+ NAD+
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Page 143
.
• Explain the terms cofactor, apoenzyme,
and coenzyme.
Page 144
.
• Discuss the effects of temperature and
pH on enzyme activity.
Page 145
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature
most effective as a catalyst at the optimal temperature
Page 146
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature
most effective as a catalyst at the optimal temperature
rate of drop-off in effectiveness away from optimal temperature depends on the enzyme
Page 147
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature
most effective as a catalyst at the optimal temperature
rate of drop-off in effectiveness away from optimal temperature depends on the enzyme
high temperatures tend to denature enzymes
Page 148
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature
most effective as a catalyst at the optimal temperature
rate of drop-off in effectiveness away from optimal temperature depends on the enzyme
high temperatures tend to denature enzymes
human enzymes have temperature optima near human body temperature (37°C)
Page 149
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH
again, most effective at the optimum; drop-off varies
Page 150
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH
again, most effective at the optimum; drop-off varies
extremes of pH tend to denature enzymes
Page 151
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH
again, most effective at the optimum; drop-off varies
extremes of pH tend to denature enzymes
a particular organism shows more variety in enzyme pH optima than in temperature optima, but most of its enzymes will still be optimal at the pH normally found in the cytosol of its cells
Page 152
.
• Discuss the effects of temperature and
pH on enzyme activity.
Page 153
.
• What is a metabolic pathway?
Page 154
.
Enzymes Metabolic pathways use organized “teams” of
enzymes
the products of one reaction often serve as substrates for the next reaction
Page 155
.
Enzymes Metabolic pathways use organized “teams” of
enzymes
the products of one reaction often serve as substrates for the next reaction
removing products (by having them participate the “next reaction”) improves reaction rate (avoids equilibrium)
Page 156
.
Enzymes Metabolic pathways use organized “teams” of
enzymes
the products of one reaction often serve as substrates for the next reaction
removing products (by having them participate the “next reaction”) improves reaction rate (avoids equilibrium)
multiple metabolic pathways exit in cells, overlapping in some areas and diverging in others
Page 158
.
• What is a metabolic pathway?
Page 159
.
• How do cells regulate enzyme activity?
– Include the terms:
• inhibitors
• activators
• allosteric site
• feedback inhibition
• Also, differentiate between:
– irreversible and reversible inhibition
– competitive and noncompetitive inhibition
Page 160
.
Enzymes
Cells can regulate enzyme activity to control reactions
increase substrate amount increase reaction rate (up to saturation of available enzyme molecules)
Page 161
.
Enzymes
Cells can regulate enzyme activity to control reactions
increase substrate amount increase reaction rate (up to saturation of available enzyme molecules)
increase enzyme amount increase reaction rate (as long as substrate amount > enzyme amount)
Page 162
.
Enzymes
Cells can regulate enzyme activity to control reactions
increase substrate amount increase reaction rate (up to saturation of available enzyme molecules)
increase enzyme amount increase reaction rate (as long as substrate amount > enzyme amount)
compartmentation of the enzyme, substrate, and products can help control reaction rate
Page 163
Rate
of
reaction
Enzyme concentration
(a) R
ate
of
rea
ctio
n
Substrate concentration
(b)
When substrate concentration >> enzyme concentration….
Page 164
.
Cells can regulate enzyme
activity to control reactions
inhibitors and activators of enzymes
activators allow or enhance catalytic activity
Page 165
.
Cells can regulate enzyme
activity to control reactions
inhibitors and activators of enzymes
activators allow or enhance catalytic activity
inhibitors reduce or eliminate catalytic activity
Page 166
.
Cells can regulate enzyme
activity to control reactions
inhibitors and activators of enzymes
activators allow or enhance catalytic activity
inhibitors reduce or eliminate catalytic activity
sometime, this uses an allosteric site – a receptor site on an enzyme where an inhibitor or activator can bind
Page 167
.
Cells can regulate enzyme
activity to control reactions
a common example of allosteric control is feedback inhibition
the last product in a metabolic pathway binds to an allosteric site of an enzyme in an early step of the pathway (often the first)
this product inhibits activity of the enzyme
Page 168
Enzyme #1 (Threonine deaminase)
Enzyme #2
Enzyme #3
Enzyme #4
Enzyme #5
Threonine
Isoleucine
-Keto-b-methylvalerate
,b-Dihydroxy-b-methylvalerate
-Aceto--hydroxybutyrate
-Ketobutyrate
Feedback inhibition
(Isoleucine inhibits enzyme #1)
Page 170
.
Cells can regulate enzyme
activity to control reactions
irreversible inhibition – enzyme is permanently inactivated or destroyed; includes many drugs and toxins
Page 171
.
Cells can regulate enzyme
activity to control reactions
irreversible inhibition – enzyme is permanently inactivated or destroyed; includes many drugs and toxins
reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered
Page 172
.
Cells can regulate enzyme
activity to control reactions
reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered
competitive inhibition – inhibitor is similar in structure to a substrate; competes with substrate for binding to the active site
Page 173
.
Cells can regulate enzyme
activity to control reactions
reversible inhibition – if inhibitor is removed, the enzyme activity can be recovered
competitive inhibition – inhibitor is similar in structure to a substrate; competes with substrate for binding to the active site
noncompetitive inhibition – binds at allosteric site, alters enzyme shape to make active site unavailable
Page 174
.
• How do cells regulate enzyme activity?
– Include the terms:
• inhibitors
• activators
• allosteric site
• feedback inhibition
• Also, differentiate between:
– irreversible and reversible inhibition
– competitive and noncompetitive inhibition