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.
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
.
• 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)?
.
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
.
Energy and Thermodynamics
energy for work: change in state or motion of matter
.
Energy and Thermodynamics
energy for work: change in state or motion of matter
expressed in Joules or calories
1 kcal = 4.184 kJ
.
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
.
Energy and Thermodynamics potential energy (capacity to
do work)
.
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
.
• 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)?
.
Energy and Thermodynamics
Laws of thermodynamics describe the constraints on energy usage…
.
• The laws of thermodynamics are
sometimes stated as:
– In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
.
Laws of Thermodynamics
First law:
the total amount of energy (+ matter) in a closed system remains constant
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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
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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
.
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.”
.
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
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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)
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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.
.
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
.
• The laws of thermodynamics are
sometimes stated as:
– In energy conversions, “You can’t win, and
you can’t break even.”
Explain.
.
• Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
.
Metabolism: anabolism + catabolism
metabolism divided into
anabolism (anabolic reactions)
anabolic reactions are processes that build complex molecules from simpler ones
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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
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• Differentiate between:
anabolism and catabolism
exergonic and endergonic reactions
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Chemical Reactions and Free Energy
Chemical reactions involve
changes in chemical bonds
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Chemical Reactions and Free Energy
Chemical reactions involve
changes in chemical bonds
changes in substance concentrations
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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
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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
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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
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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
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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)
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Chemical Reactions and Free Energy
catabolic reactions are usually exergonic
ATP + H2O ADP + Pi is highly exergonic
.
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)
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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
.
Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
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Chemical Reactions and Free Energy
How to get energy for an endergonic reaction?
couple with an exergonic one!
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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
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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)
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Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
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Chemical Reactions and Free Energy
EXAMPLE:
A B (exergonic)
C D (endergonic)
Coupled: A + C B + D (overall exergonic)
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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
.
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
.
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…
.
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
.
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?
.
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.
.
ATP is the main energy currency in cells
ATP – nucleotide with adenine base, ribose sugar, and a chain of 3 phosphate groups
.
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:
.
ATP is the main energy currency in cells
hydrolysis of ATP to ADP and inorganic phosphate (Pi) releases energy
ATP + H2O ADP + Pi
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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
.
ATP is the main energy currency in cells
Intermediates when ATP hydrolysis is coupled to a reaction to provide energy
.
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
.
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
.
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
.
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)
.
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)
.
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
.
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
.
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)
.
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
.
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
.
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
.
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)
.
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
.
ATP is the main energy currency in cells
Cells maintain high levels of ATP relative to ADP
maximizes energy available from hydrolysis of ATP
.
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
.
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
.
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
.
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
.
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?
.
• 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.
.
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.
.
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 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)
.
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
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
+
.
Redox reactions are also used for
energy transfer
chain of redox reactions / electron transfers common
more on electron transport chains later
.
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
.
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
.
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
.
Redox reactions are also used for
energy transfer intermediate acceptor example: nicotinamide adenine dinucleotide (NAD+)
.
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+
.
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
.
Redox reactions are also used for
energy transfer
Reduced state stores energy, which
is partially released as free energy
when NADH is oxidized
.
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
.
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
.
• 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.
.
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
.
• 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
.
Enzymes
Manipulation of reactions is essential to and largely defining of life.
.
Enzymes
Manipulation of reactions is essential to and largely defining of life.
Organisms use enzymes to manipulate the speed of reactions.
.
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.
.
Enzymes Enzymes regulate chemical reactions in living organisms
An enzyme is an organic molecule (typically a protein)
that acts as a catalyst
.
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 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
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.
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
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
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
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
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
.
Enzymes work by lowering activation energy of a reaction
all reactions have a required energy of activation
.
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
.
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
.
Enzymes
activation energy
catalysts greatly reduce the activation energy
requirement, making it easier for a reaction to occur
.
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
.
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
.
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
.
Enzymes
ES complex typically very unstable
.
Enzymes
ES complex typically very unstable
short-lived
.
Enzymes
ES complex typically very unstable
short-lived
breaks down into released product(s) and a free enzyme that is ready to be reused
.
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)
.
• 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
.
• What are the four main things that
enzymes do to lower activation energy?
.
Enzymes reduction in activation energy is due primarily to four things:
.
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
.
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
.
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
.
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
.
Enzymes enzyme + substrate(s) ES complex enzyme + product(s)
.
• What are the four main things that
enzymes do to lower activation energy?
.
• How are enzymes named (what suffixes
indicate an enzyme)?
.
Enzymes Enzyme names
many names give some indication of substrate
.
Enzymes Enzyme names
many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)
.
Enzymes Enzyme names
many names give some indication of substrate
most enzyme names end in –ase (example: sucrase)
some end in –zyme (example: lysozyme)
.
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)
.
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
.
Enzymes
the amount of specificity depends on the particular enzyme
example of high specificity: sucrase splits sucrose, not other disaccharides
.
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
.
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/
.
• How are enzymes named (what suffixes
indicate an enzyme)?
.
• Explain the terms cofactor, apoenzyme,
and coenzyme.
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
.
Enzymes Many enzymes require additional chemical
components (cofactors) to function
apoenzyme + cofactor active enzyme (bound together)
.
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
.
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
.
Enzymes cofactors can be organic or inorganic
organic examples (coenzymes):
ADP, NAD+, NADP+, FAD
typically changed by the catalyzed reaction
.
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
.
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
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+
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.
• Explain the terms cofactor, apoenzyme,
and coenzyme.
.
• Discuss the effects of temperature and
pH on enzyme activity.
.
Enzymes are most active under optimal conditions
each enzyme has an optimal temperature
most effective as a catalyst at the optimal temperature
.
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
.
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
.
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)
.
Enzymes are most active under optimal conditions
each enzyme has an optimal pH
again, most effective at the optimum; drop-off varies
.
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
.
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
.
• Discuss the effects of temperature and
pH on enzyme activity.
.
Enzymes Metabolic pathways use organized “teams” of
enzymes
the products of one reaction often serve as substrates for the next reaction
.
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)
.
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
.
• 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
.
Enzymes
Cells can regulate enzyme activity to control reactions
increase substrate amount increase reaction rate (up to saturation of available enzyme molecules)
.
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)
.
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
Rate
of
reaction
Enzyme concentration
(a) R
ate
of
rea
ctio
n
Substrate concentration
(b)
When substrate concentration >> enzyme concentration….
.
Cells can regulate enzyme
activity to control reactions
inhibitors and activators of enzymes
activators allow or enhance catalytic activity
.
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
.
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
.
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
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)
.
Cells can regulate enzyme
activity to control reactions
irreversible inhibition – enzyme is permanently inactivated or destroyed; includes many drugs and toxins
.
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
.
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
.
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
.
• 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