Chapter 14
Principles of
Bioenergetics
1,Cells need energy to do all their
work
? To generate and maintain its highly ordered
structure (biosynthesis of macromolecules).
? To generate all kinds of movement.
? To generate concentration and electrical gradients
across cell membranes.
? To maintain a body temperature.
? To generate light in some animals.
? The,energy industry”(production,storage and use)
is central to the economy of the cell society!
? Bioenergetics (生物能学 ）, the quantitative
study of energy transductions in living cells and
the chemical nature underlying these processes.
2,Cells have to use chemical energy
to do all their work
? Antoine Lavoisier`s insight on animal respiration in
the 18th century,it is nothing but a slow combustion
of carbon and hydrogen (the same nature as a
lighting candle).
? Living cells are generally held at constant
temperature and pressure,chemical energy (free
energy) has to be used by living organisms,no
thermal energy,neither mechanical energy is
available to do work in cells.
? Biological energy transformation obey the two basic
laws of thermodynamics revealed by physicists and
chemists in the 19th century,energy can neither be
created nor be destroyed (but conserved); energy
conversion is never 100% efficient (some will
always be wasted in increasing the disorder or
“entropy” of the universe).
? The free energy concept of thermodynamic is more
important to biochemists than to chemists (who can
always increase the temperature and pressure to
make a reaction to occur!).
3,Application of the free energy (G)
concept to biochemical reactions
? Free energy (G),the amount of energy available
to do work during a reaction at a constant
temperature and pressure; change,not absolute
value can be measured.
? Free energy change (?G),The free energy
difference between the products and the reactants.
? Gibbs observation,under constant temperature
and pressure,all systems change in such a way
that free energy is minimized (products should
have less free energy than reactants for a reaction
to occur spontaneously,i.e.,?G has a negative
value ).
? Spontaneity has nothing to do with rate!
? Standard free energy change in biochemistry
(?G'o),value of the change in free energy under
conditions of 298 K (25oC),1 atm pressure,pH
7.0 (chemists use pH 0,i.e.,the concentration of
H+ they use is 1M,not 10-7 M as biochemists use
here) and initial concentrations of 1 M for all
reactants and products (except H+).
? The actual free energy chang (?G )depends on
?G'o,temperature,ratio of product and reactant
concentrations (Q):
? ?G = ?G'o + RT ln Q
? Enzymes only speed up thermodynamically
favorable reactions (having a negative ?G) !
? ?G'o is related to the equilibrium constant K'eq
(the prime again indicates its biochemical
transformation),at equilibrium,?G = 0,Q = K`eq,
thus
? ?G' o = -RT ln K'eq
? The ?G and ?G'o values are additive when
reactions are coupled (i.e.,sharing common
intermediates),thus a thermodynamically
unfavorable reaction can be driven by a favorable
one,
? The overall K`eq is multiplicative (the product of
two,两值相乘 ),although ?G'o is additive (the
algebraic sum of two,两值相加 ).
4,ATP is the universal currency
for biological energy
? This was first perceived by Fritz Lipmann and
Herman Kalckar in 1941 when studying glycolysis.
? Hydrolysis of the two phosphoanhydride (磷酸酐键 )
bonds in ATP generate more stable products
releasing large amount of free energy (?G'o is -30.5
kJ/mol; ?G in cells is -50 to -65 kJ/mol).
? The ATP molecule is kinetically stable at pH 7 (i.e.,
it has a high activation energy,?G? for hydrolysis)
and enzyme catalysis is needed for its hydrolysis.
? ATP is not a long-term storage form of free
energy in living cells,being consumed within a
minute following its formation (phosphocreatine,
磷酸肌酸,act as a energy storage form for
longer term).
? A resting human consumes about 40 kg of ATP
in 24 hours!
? ATP provides energy by group transfer
(donating a Pi,PPi or AMP to form covalent
intermediates),not by simple hydrolysis.
? ATP has an intermediate phosphoryl group
transfer potential,thus ADP can accept and ATP
can donate phosphoryl groups.
? In the lab,as little as a few picomoles (10-12 mol)
of ATP can be measured using firefly luciferin
and luciferase (荧光素酶 ),using spectroscopic
methods.
? Inorganic polyphosphate could have served as an
energy source in prebiotic and early cellular
evolution.
ATP provides energy
usually through group
transfer,thus Activating
the substrate
ATP has an intermediate
phosphoryl group transfer
potential
ATP can transfer a Pi,PPi or AMP to a reactant
Picomoles (10-12 mol) of ATP can be measured
Using leciferase
Inorganic polyphosphate may act as
an energy storage form
5,Electron transfer via redox
reactions generates biological energy
? When electrons flow from a low affinity carrier
(reductant) to a high affinity carrier (oxidant),either
in an electric battery or in a living cell,energy is
released and work can be done.
? Oxidation of energy-rich biological fuels often
means dehydrogenation (catalyzed by
dehydrogenases,脱氢酶 ) from carbons having
various oxidation states.
? In the living cells,electrons are transferred directly
as electrons (between metal ions),as hydrogen
atoms (H++e-),or as a hydride ion (:H- or H++2e-).
? The affinity for electrons of a compound (in its
oxidized form) is indicated by its reduction
potential (E).
? Standard reduction potential (E'o) of each oxidant
(a constant) is measured by connecting a half-cell
having the oxidized and reduced species of the
redox pair each at 1 M,or 1 atm for gases,pH 7
to a reference half-cell having 1 M H+ and 1 atm
H2,whose E' o is arbitrarily assigned as 0.00 V.
? A positive value of E'o indicates a tendency to
acquire electron from the reference half cell
(with 1M H+/1atm H2).
? The actual reduction potential (E) depends on,
electrons transferred per molecule,temperature,
ratio of [electron acceptor]/[electron donor]:
? ?G'o of a redox reaction can be calculated from
the ?E'o of the two redox pairs:
Energy is
“generated” via
electron flow
both in a battery
and in a cell!
Carbons have various oxidation states,
with hydrocarbon being the most
reduced and CO2 being the most
oxidizaed.
The carbon atom may,own” different number of electrons in
different compounds,thus having different oxidation states
The standard reduction
potential (E'o) of a
conjugate redox pair
is measured by
connecting the sample
half cell to the H+/H2
reference half cell.
6,A few universal carriers (as
coenzymes) collect electrons from the
oxidation of various substrates
? NAD+,NADP+,FAD are the few commonly used
such reversible electron carriers.
? NAD and NADP are dinucleotides able to
accept/donate a hydride ion (thus with 2e-) for each
round of reduction/oxidation.
? Reduction of NAD+ and NADP+ can be easily
followed by spectroscopy (at 340 nm).
? In each specific NAD- or NADP-containing
dehydrogenase,the hydride ion is added/taken
stereospecifically from one side (A or B) of the
nicotinamide (烟碱 ) ring.
? FAD is able to accept/donate one or two electrons
(as hydrogen atom),with absorption maximum
shifts from 570 nm to 450nm.
? NAD and NADP can easily diffuse out of the
enzymes,but FMN and FAD are tightly bound to
the enzymes.
? ADP is commonly present all these universal
electron carriers (as well as in Coenzyme A and
ATP),suggesting that RNA catalyzed these
reactions in the early stages of life.
? They serve as cofactors of various enzymes
catalyzing the oxidation of nutrients.
? NADH and FADH2 will be further oxidized via the
respiratory chain on the inner membrane of
mitochondria or plasma membrane of bacteria for
energy generation (transduction).
:H-
Nicotinamide is derived
From niacin (a vitamin)
NAD (Nicotinamide Adenine Dinucleotide) and
NADP (Nicotinamide Adenine Dinucleotide
Phosphate)
Nicotinamide
Reactive
sites FMN (Flavin
MonoNucleotide) and
FAD (Flavin Adenine
Dinucleotide)
异咯嗪环
Summary
? Bioenergy is chemical energy,studied in terms of
free energy and free energy change (?G ).
? ATP acts as the free energy carrier in cells.
? Bioenergy is mainly produced via stepwise electron
flow (redox reactions) through a series of electron
carriers having increasing levels of reduction
potential (E).
? Electrons released from the oxidation of nutrient
fuels are initially channeled to a few universal
electron carriers (including NADH and FADH2).
References
? Alberty,R,A,(1994),Biochemical themodynamics”
Biochim,Biophys,Acta,1207:1-11.
? Frey,P,A,and Arabshahi,A,(1995),Standard free
energy change for hydrolysis of the a-b
phosphoanhydride bridge in ATP” Biochemistry,
34:11307-11310.
? Westheimer,F.H.,(1987),Why nature chose
phosphates” Science,235:1173-1178.
? Kornberg,A et al,(1999),Inorganic polyphosphate,
a molecule of many functions” Annu,Rev,Biochem,
68:89-125.
Principles of
Bioenergetics
1,Cells need energy to do all their
work
? To generate and maintain its highly ordered
structure (biosynthesis of macromolecules).
? To generate all kinds of movement.
? To generate concentration and electrical gradients
across cell membranes.
? To maintain a body temperature.
? To generate light in some animals.
? The,energy industry”(production,storage and use)
is central to the economy of the cell society!
? Bioenergetics (生物能学 ）, the quantitative
study of energy transductions in living cells and
the chemical nature underlying these processes.
2,Cells have to use chemical energy
to do all their work
? Antoine Lavoisier`s insight on animal respiration in
the 18th century,it is nothing but a slow combustion
of carbon and hydrogen (the same nature as a
lighting candle).
? Living cells are generally held at constant
temperature and pressure,chemical energy (free
energy) has to be used by living organisms,no
thermal energy,neither mechanical energy is
available to do work in cells.
? Biological energy transformation obey the two basic
laws of thermodynamics revealed by physicists and
chemists in the 19th century,energy can neither be
created nor be destroyed (but conserved); energy
conversion is never 100% efficient (some will
always be wasted in increasing the disorder or
“entropy” of the universe).
? The free energy concept of thermodynamic is more
important to biochemists than to chemists (who can
always increase the temperature and pressure to
make a reaction to occur!).
3,Application of the free energy (G)
concept to biochemical reactions
? Free energy (G),the amount of energy available
to do work during a reaction at a constant
temperature and pressure; change,not absolute
value can be measured.
? Free energy change (?G),The free energy
difference between the products and the reactants.
? Gibbs observation,under constant temperature
and pressure,all systems change in such a way
that free energy is minimized (products should
have less free energy than reactants for a reaction
to occur spontaneously,i.e.,?G has a negative
value ).
? Spontaneity has nothing to do with rate!
? Standard free energy change in biochemistry
(?G'o),value of the change in free energy under
conditions of 298 K (25oC),1 atm pressure,pH
7.0 (chemists use pH 0,i.e.,the concentration of
H+ they use is 1M,not 10-7 M as biochemists use
here) and initial concentrations of 1 M for all
reactants and products (except H+).
? The actual free energy chang (?G )depends on
?G'o,temperature,ratio of product and reactant
concentrations (Q):
? ?G = ?G'o + RT ln Q
? Enzymes only speed up thermodynamically
favorable reactions (having a negative ?G) !
? ?G'o is related to the equilibrium constant K'eq
(the prime again indicates its biochemical
transformation),at equilibrium,?G = 0,Q = K`eq,
thus
? ?G' o = -RT ln K'eq
? The ?G and ?G'o values are additive when
reactions are coupled (i.e.,sharing common
intermediates),thus a thermodynamically
unfavorable reaction can be driven by a favorable
one,
? The overall K`eq is multiplicative (the product of
two,两值相乘 ),although ?G'o is additive (the
algebraic sum of two,两值相加 ).
4,ATP is the universal currency
for biological energy
? This was first perceived by Fritz Lipmann and
Herman Kalckar in 1941 when studying glycolysis.
? Hydrolysis of the two phosphoanhydride (磷酸酐键 )
bonds in ATP generate more stable products
releasing large amount of free energy (?G'o is -30.5
kJ/mol; ?G in cells is -50 to -65 kJ/mol).
? The ATP molecule is kinetically stable at pH 7 (i.e.,
it has a high activation energy,?G? for hydrolysis)
and enzyme catalysis is needed for its hydrolysis.
? ATP is not a long-term storage form of free
energy in living cells,being consumed within a
minute following its formation (phosphocreatine,
磷酸肌酸,act as a energy storage form for
longer term).
? A resting human consumes about 40 kg of ATP
in 24 hours!
? ATP provides energy by group transfer
(donating a Pi,PPi or AMP to form covalent
intermediates),not by simple hydrolysis.
? ATP has an intermediate phosphoryl group
transfer potential,thus ADP can accept and ATP
can donate phosphoryl groups.
? In the lab,as little as a few picomoles (10-12 mol)
of ATP can be measured using firefly luciferin
and luciferase (荧光素酶 ),using spectroscopic
methods.
? Inorganic polyphosphate could have served as an
energy source in prebiotic and early cellular
evolution.
ATP provides energy
usually through group
transfer,thus Activating
the substrate
ATP has an intermediate
phosphoryl group transfer
potential
ATP can transfer a Pi,PPi or AMP to a reactant
Picomoles (10-12 mol) of ATP can be measured
Using leciferase
Inorganic polyphosphate may act as
an energy storage form
5,Electron transfer via redox
reactions generates biological energy
? When electrons flow from a low affinity carrier
(reductant) to a high affinity carrier (oxidant),either
in an electric battery or in a living cell,energy is
released and work can be done.
? Oxidation of energy-rich biological fuels often
means dehydrogenation (catalyzed by
dehydrogenases,脱氢酶 ) from carbons having
various oxidation states.
? In the living cells,electrons are transferred directly
as electrons (between metal ions),as hydrogen
atoms (H++e-),or as a hydride ion (:H- or H++2e-).
? The affinity for electrons of a compound (in its
oxidized form) is indicated by its reduction
potential (E).
? Standard reduction potential (E'o) of each oxidant
(a constant) is measured by connecting a half-cell
having the oxidized and reduced species of the
redox pair each at 1 M,or 1 atm for gases,pH 7
to a reference half-cell having 1 M H+ and 1 atm
H2,whose E' o is arbitrarily assigned as 0.00 V.
? A positive value of E'o indicates a tendency to
acquire electron from the reference half cell
(with 1M H+/1atm H2).
? The actual reduction potential (E) depends on,
electrons transferred per molecule,temperature,
ratio of [electron acceptor]/[electron donor]:
? ?G'o of a redox reaction can be calculated from
the ?E'o of the two redox pairs:
Energy is
“generated” via
electron flow
both in a battery
and in a cell!
Carbons have various oxidation states,
with hydrocarbon being the most
reduced and CO2 being the most
oxidizaed.
The carbon atom may,own” different number of electrons in
different compounds,thus having different oxidation states
The standard reduction
potential (E'o) of a
conjugate redox pair
is measured by
connecting the sample
half cell to the H+/H2
reference half cell.
6,A few universal carriers (as
coenzymes) collect electrons from the
oxidation of various substrates
? NAD+,NADP+,FAD are the few commonly used
such reversible electron carriers.
? NAD and NADP are dinucleotides able to
accept/donate a hydride ion (thus with 2e-) for each
round of reduction/oxidation.
? Reduction of NAD+ and NADP+ can be easily
followed by spectroscopy (at 340 nm).
? In each specific NAD- or NADP-containing
dehydrogenase,the hydride ion is added/taken
stereospecifically from one side (A or B) of the
nicotinamide (烟碱 ) ring.
? FAD is able to accept/donate one or two electrons
(as hydrogen atom),with absorption maximum
shifts from 570 nm to 450nm.
? NAD and NADP can easily diffuse out of the
enzymes,but FMN and FAD are tightly bound to
the enzymes.
? ADP is commonly present all these universal
electron carriers (as well as in Coenzyme A and
ATP),suggesting that RNA catalyzed these
reactions in the early stages of life.
? They serve as cofactors of various enzymes
catalyzing the oxidation of nutrients.
? NADH and FADH2 will be further oxidized via the
respiratory chain on the inner membrane of
mitochondria or plasma membrane of bacteria for
energy generation (transduction).
:H-
Nicotinamide is derived
From niacin (a vitamin)
NAD (Nicotinamide Adenine Dinucleotide) and
NADP (Nicotinamide Adenine Dinucleotide
Phosphate)
Nicotinamide
Reactive
sites FMN (Flavin
MonoNucleotide) and
FAD (Flavin Adenine
Dinucleotide)
异咯嗪环
Summary
? Bioenergy is chemical energy,studied in terms of
free energy and free energy change (?G ).
? ATP acts as the free energy carrier in cells.
? Bioenergy is mainly produced via stepwise electron
flow (redox reactions) through a series of electron
carriers having increasing levels of reduction
potential (E).
? Electrons released from the oxidation of nutrient
fuels are initially channeled to a few universal
electron carriers (including NADH and FADH2).
References
? Alberty,R,A,(1994),Biochemical themodynamics”
Biochim,Biophys,Acta,1207:1-11.
? Frey,P,A,and Arabshahi,A,(1995),Standard free
energy change for hydrolysis of the a-b
phosphoanhydride bridge in ATP” Biochemistry,
34:11307-11310.
? Westheimer,F.H.,(1987),Why nature chose
phosphates” Science,235:1173-1178.
? Kornberg,A et al,(1999),Inorganic polyphosphate,
a molecule of many functions” Annu,Rev,Biochem,
68:89-125.
