energy metabolism
TRANSCRIPT
Energy Metabolism
MARI-ANN BENIGNO-BRINGAS, MD
Department of Biochemistry & Nutrition
FEU-NRMF Institute of Medicine
Foodstuff
CHO, CHON,FA
oxidized
Glycolysis
TCA cycleFA oxidation
producesCO2
ATPReducing Equivalents
ELECTRON TRANSPORT CHAIN
oxidized
Endergonic and
phosphorylation
reactions
Energy-requiring
processes
utilized by
ADP + Pi
release
utilized by
Molecular O2
reduced
H2O
produces
I. Bioenergetics
A. Laws of Thermodynamics
B. Thermodynamic Concepts
C. ATP & Phosphagens
II. Biologic Oxidation
A. Redox Potential
III. The Electron Transport Chain
A. Reducing Equivalents, Carriers, Shuttles
B. Oxidative Phosphorylation
C. Poisons of the ETC
Energy Metabolism
Bioenergetics - study of energy transformation that
accompanies biochemical reactions.
All living organisms are open systems –
they exchange matter & energy with the
environment
All organisms exist in a steady state –
rate of transfer in and out of the system is
constant
Living organisms are essentially isothermal
Energy Metabolism
1st: Law of Energy Conservation
The total energy of a system + surroundings is
constant
Mass and energy can be inter-converted
May be written as:
E = Q - W
E = change in energy of a system
Q = heat absorbed by the system
W = work done by the system
Laws of Thermodynamics
Bioenergetics
2nd: Law of Entropy
The entropy of a system + surrounding increases until
equilibrium is achieved
Maximal at equilibrium
The entropy change is positive for every process
Laws of Thermodynamics
Bioenergetics
Thermodynamic Concepts
Enthalpy (H)
Entropy (S)
Free Energy (G)
H = G + T S ; where T= absolute temp.
Change in enthalpy = change in free energy + T [change in entropy]Change in total energy = change in useful energy + change in fixed energy
of organization
Bioenergetics
Enthalpy (H) - the heat content of a system
H = E + PV E = internal energy
P = pressure
V = volume
exothermic - heat is given off [ ∆H = negative]
endothermic - heat is absorbed [∆H = positive]
isothermic - no net exchange of heat [∆H = 0]
Calorimetry - the measurement of heat flow
Thermodynamic Concepts
Entropy (S) - the degree of disorder of the system
G = H + T (S) T = temperature
H = enthalpy
G = free energy
refers to the portion of the total energy that is
not available to perform work
this cannot be measured directly
diluting a solution will increase its entropy
Thermodynamic Concepts
RELATIONSHIP BETWEEN CHANGES IN FREE ENERGY,
ENTHALPY AND ENTROPY
CHANGE IN ENTHALPY• Heat released or absorbed during a reaction
• Does not predict whether a reaction is favorable
CHANGE IN FREE ENERGY• Energy available to do work
• Approaches 0 as reaction
approaches equilibrium
• Predicts whether a reaction is
favorable
CHANGE IN ENTROPY• Measure of randomness
• Does not predict whether a
reaction is favorable
Free Energy (G) - the portion of the total energy that
can support useful work;
- introduced by Josiah Gibbs
Free Energy Change [G] - the change in the amount of
useful energy as the system proceeds towards equilibrium
Standard Free Energy Change [Go’] - the change in
free energy of a given equation under standard conditions
Go’2.303-= RT log Keq R = gas constant
T = absolute temperature
Keq = equilibrium
constant
Thermodynamic Concepts
Standard state : pH = 7.0
Temp = 25o C or 298o K
[Solute] = 1 Molar
Pressure = 1 atm; 760 mmHg
Thermodynamic Concepts
Standard Free Energy Change
- does not measure the velocity of the reaction
- does not measure the rate at which equilibrium can be
achieved
- diluting a given solution will decrease its free energy
- predicts the spontaneity of reactions
- The change in free energy that occurs when a compound is formed form its elements in their most thermodynamically stable states at standard-state conditions.
FREE ENERGY is energy that is available for doing work
just like water spontaneously falling from a higher to a lower ground,
ALL systems tend to proceed towards equilibrium,
where there will be no net change in free energy
Standard Free Energy Change
endergonic - free energy is absorbed [Go’ = positive]
exergonic - free energy is generated [Go’ = negative]
isoergonic - equilibrium, the Go’ is zero
with regards to spontaneity,
endergonic reactions cannot occur spontaneously
exergonic reactions can occur spontaneously
Thermodynamic Concepts
Free Energy Change
Biologic systems
Biochemical reactions
Redox reactions
Coupled Reactions = endergonic + exergonic
Catabolic processes are coupled to anabolic processes
Thermodynamic Concepts
Glucose + Pi Glucose-6-P Go’ = + 3.3 Kcal/mol [endergonic]
ATP ADP + Pi Go’ = - 7.3 Kcal/mol [exergonic]
Glucose + ATP G6P + ADP Go’ = - 4.0 Kcal/mol [exergonic]
Compartmentalization of the different processes allows
them to co-exist within the cell
Hydrogenation-Dehydrogenation reactions
- co-factor: Mg++
- aka “energy currency of the cell”
[Lipmann Law]
~ PPP ~
The ATP
ATP [Adenosine triphosphate]
~ PPP ~
G= -7.3 Kcal/mol
ATP ADP + Pi
ATP AMP + PPi
G= -7.7 Kcal/mol
PPi 2 PiG= -8 Kcal/mol
The ATP
The ATP
QUESTION:
Why is ADP + Pi more
stable than ATP?
The ATP
ATP participates covalently
in the enzyme-catalyzed
reaction to which it
contributes free energy
some processes involve
direct hydrolysis:
- muscle contraction
- movement of enzymes
along DNA or ribosomes
along mRNA
ATP provides energy by group
transfer, not by simple hydrolysis
OrganoPO4 compound Go’ (Kcal/mol)
phosphoenolpyruvate (PEP) -14.8
carbamoyl phosphate -12.3
1,3-bisphophoglycerate -11.8
creatine phosphate -10.3
ATP -7.3
ADP -6.6
Glucose-1-phosphate -5.0
AMP -3.4
Glucose-6-phosphate -3.3
The ATP
Hydrolysis of organophosphates
Sources of ATP
1) ETC - via oxidative phosphorylation [3 ATPs]
2) Glycolysis - via substrate-level phosphorylation [2 ATPs]
3) Kreb’s Cycle - via substrate-level phosphorylation [1 ATP]
Phosphagens - high energy compounds that serve as
energy reservoirs
1) Creatine phosphate - in vertebrates
2) Arginine phosphate - in invertebrates
3) Polymetaphosphate [metachromatic, volutin granules]
- in microorganisms
The ATP
Kreb’s Cycle Glycolysis
Sources of ATP
The ATP
(2 ATPs) (1 ATP) (3 ATPs)
Oxidation - losing electrons [dehydrogenation, valence]
e-
Fe ++ Fe +++
reduced oxidized
Biologic Oxidation
2H+ + ½ O2 + 2e- H2 O (Reduction half reaction)
NADH NAD+ + H+ + 2e- (Oxidation half reaction)
Reduction - gaining electrons [hydrogenation, valence]
Fe++ + Cu++ Fe+++ + Cu+
R. A. O. A. O. A. R. A.
Standard Redox Potential [SRP]
- measures the tendency of a biologic system to
release or accept electrons;
- expressed in volts (E°)
Biologic Oxidation
“ the more negative the Eo’, the better reductant ”
“ the more positive the Eo’, the better oxidant ”
Redox Couple Eo’ (volt) n
-ketoglutarate isocitrate - 0.36 2
NAD NADH + H - 0.32 2
FAD FADH2 - 0.22 2
pyruvate lactate - 0.19 2
oxaloacetate malate - 0.17 2
fumarate succinate - 0.03 2
UQ UQH + 0.03 1
Cyt c (Fe+++) Cyt c (Fe++) + 0.24 1
oxygen water + 0.82 4
Best Reductant
Best Oxidant
e-
(-)
(+)
Biologic OxidationStandard Redox Potential [SRP]
Redox Reactions
Oxaloacetate + 2H+ + 2e- malate Eo’ = - 0.17 v (Red)
NAD+ + H+ + 2e- NADH + H+ Eo’ = - 0.32 v (Red)
Oxaloacetate + 2H+ + 2e- malate Eo’ = - 0.17 v (Red)
OA + NADH + H+ malate + NAD+ Eo’ = 0.15 vNET:
Go’ = - n F (Eo’ ) n = no. of electrons
= - (2)(23.061 Kcal/v.mol)(0.15v) F = Faraday’s c.
= - 6.92 Kcal/mol (23.061 Kcal/volt-mol)
Biologic Oxidation
NADH + H+ NAD+ + H+ + 2e- Eo’ = 0.32 v (Ox)
The Mitochondrion
Outer mitochondrial
membrane
CytoplasmGlycolysis
Mitochondrial matrix
Kreb’sCycle,UreaCycle, -oxidation
Inner mitochondrial
membrane
ETC, Succinate DH, ATP synthase
The Electron Transport Chain
Intermembrane space
The Electron Transport Chain
OMM
Outer mitochondrial membrane
permeable to most small
molecules
IMS
Inner mitochondrial membrane
has similar environment and
substrates with cytoplasm
IMM
Inner mitochondrial membrane
high selectivity with transport
systems
Electron Carriers
1) NAD
- derived from Niacin (Vitamin B3)
- active portion is the nicotinamide ring
- carries 2 electrons but only one H+ NADH+H+
2) FAD
- derived from Riboflavin (Vitamin B2)
- active portion is the isoalloxazine ring
- carries 2 electrons and 2 H+ FADH2
The Electron Transport Chain
NAD/NADH + H+
FAD/FADH2
Flavin adenine dinucleotide (FAD) is also a
biological oxidizing agent
Protons, as well as, electrons are accepted by
FAD
The Structures of Riboflavin, Flavin Mono-nucleotide (FMN), and Flavin Dinucleotide (FAD)
Shuttle Systems
1) Malate-Aspartate Shuttle System
- involves transamination between OAA & Glutamate
- major shuttle system in the liver and heart cells
- uses NAD as mitochondrial e- carrier
2) Glycerol-3-phosphate Shuttle System
- uses Glycerol-3-phosphate Dehydrogenase
- major shuttle system in the brain and myocytes
- uses FAD as mitochondrial e- carrier
The ETC
ETC
The ETC
Malate-Aspartate Shuttle System
Cytosol Matrix
NADH + H+
Oxaloacetate
Malate NAD+ Malate
Oxaloacetate
Aspartate
Glutamate Glutamate
Aspartate
-ketoglutarate -ketoglutarate
NADH + H+
NAD+
Glycerol-3-phosphate Shuttle System
The ETC
Cytosol Matrix
NADH + H+
NAD+ DHAP
Glycerol-3-phosphate
ETC
FADH2
ATP
ATP
ATP
GLUCOSE
GLU-6-PO4
PYRUVATE
ACETYL COA
NADH
NADH
NADH
NADH
FADH2
KREBS
The ETC
Components of the ETC
The ETC
Components of the ETC
1) Cytochromes
- with an Fe++ in a porphyrin ring
- single-electron carriers
- Cytochrome c = mobile, water-soluble protein
2) Ubiquinone [Coenzyme Q]
- a non-protein isoprenoid quinone
- another mobile component; most abundant
- shares structural homology with Vitamin E & K
The ETC
Components of the ETC
3) Fe-Sulfur Complexes
- associated with metalloflavoproteins & Cyt b
- single-electron carriers involved in the redox
mechanism between flavin and Q
4) Molecular Oxygen
- the final acceptor of electrons along the ETC
- can accommodate 4 electrons to form H2O
The ETC
The Various ETC Complexes
NADH
FADH2
CoQ Cyt b, c1 Cyt c Cyt aa3
Complex I
NADH Coenzyme Q reductase
The ETC
The Various ETC Complexes
NADH
FADH2
CoQ Cyt b, c1 Cyt c Cyt aa3
Complex II
Succinate Coenzyme Q reductase
The ETC
The Various ETC Complexes
CoQ Cyt b, c1 Cyt c Cyt aa3
Complex III
Coenzyme Q-Cytochrome C reductase
NADH
FADH2
The ETC
The Various ETC Complexes
NADH +H
FADH2
CoQ Cyt b, c1 Cyt c Cyt aa3
Complex IV
Cytochrome oxidase
The Various ETC Complexes
NADH+H
FADH2
CoQ Cyt b, c1 Cyt c Cyt aa3
Complex IVCytochrome
oxidase
Complex IIICoQ-cytochrome
reductase
Complex II succinate dehydrogenase
Complex I NADH
dehydrogenase
Points of entry - Complex I and II
Mobile components - CoQ and Cytochrome c
The ETC
The ETC
Sites of Proton Translocation
The ETC
1) Chemical Coupling Hypothesis
- generation of high energy intermediates at
ATP-forming sites
2) Conformational Hypothesis
- the free energy released is stored as a
conformational change in the respiratory proteins
3) Chemiosmotic Theory [1961]
- postulated by Peter Mitchell
- the accepted mechanism that explains Oxidative
phosphorylation
Oxidative Phosphorylation
The Chemiosmotic Theory
IMM
IMS
Matrix
I III IVII
Free energy
e- e-
The ETC
The Chemiosmotic Theory
IMM
IMS
Matrix
I III IVII
H+ H+ H+
4H+ 4H+ 2H+
Proton pumps - I and IV
Redox loop - III
The ETC
IMM
IMS
Matrix
I III IVII
Electro-chemical gradient Protonmotive force [PMF]
H+ H+ H+
4H+ 4H+ 2H+
pH, Q+
pH, Q-
The Chemiosmotic Theory
The ETC
The Chemiosmotic Theory
IMM
IMS
Matrix
I III IVII
4H+ 4H+ 2H+
proticity
ADP + Pi ATP
The ETC
The Chemiosmotic Model
The ETC
The Chemiosmotic Theory
IMM
IMS
Matrix
I III IVII
Fo
F1
Stalk (OSCP)
v
ATP Synthase
The ETC
“Binding change” mechanism
IMM
IMS
Matrix
I III IVII
4H+ 4H+ 2H+
ADP + Pi(spontaneous)
ATP release
The ETC
3H+
The ETC
The P:O ratio
• A quantitative expression of determining the extent of ATP formation
during electron transport
• The ratio of the moles of ATP formed per atom of oxygen used.
• The number of moles of Pi consumed in phosphorylation to the
number of moles of oxygen atoms consumed in oxidation
NADH P:O ratio = 2.5 ~ 3 ATPs
FADH2 P:O ratio = 1.5 ~ 2 ATPs
• Phosphorylation: ADP + Pi ----> ATP + H2O
• Oxidation: 1/2O2 + 2H+ + 2e- ---> H2O
The ETC
The P:O ratio
IMM
IMS
Matrix
I
III IVII
H+ H+ H+
4H+ 4H+ 2H+
3H+ 1H+
ATP
ADP Pi
OH-
ADP + Pi
(spontaneous)
ATP release
The Site-specific Inhibitors
IMM
IMS
Matrix
I III IVII
Amobarbital
Piericidin A
Rotenone
The ETC
Barbiturate –Rx Insomnia, anxiety
inhibitor of NADH dehydrogenase
Insecticide produced by extraction from the roots and stems of several tropical and subtropical plant species, especially those belonging to the genera Lonchocarpus and Derris.
The Site-specific Inhibitors
IMM
IMS
Matrix
I III IVII
Carboxin
TTFA
Malonate
The ETC
systemic anilide fungicide.
Thenoyltrifluoroacetone –conventional complex II inhibitor
The Site-specific Inhibitors
IMM
IMS
Matrix
I III IVII
Dimercaprol
Antimycin
The ETC
used medically in treatment of arsenic, mercury, gold, lead, and other toxic metal poisoning.
Fish poison used in fisheries management and in catfish industry
The Site-specific Inhibitors
IMM
IMS
Matrix
I III IVII
Cyanide
Hydrogen sulfide
Carbon monoxide
The ETC
Oligomycin
- an antibiotic that binds to the OSCP
[complex V inhibitor]
Atractyloside
- a toxic plant glycoside that inhibits the
ADP-ATP transporter
Aurovertin
- Aurovertin inhibits oxidative phosphorylation in
mitochondria in much the same way as oligomycin.
Oligomycin and aurovertin, applied in amounts less than
those maximally effective, have additive effects on the
inhibition of oxidative phosphorylation,
The Non-site-specific Inhibitors
The ETC
ETC
The Uncouplers
IMM
IMS
Matrix
I III IVII
4H+ 2H+ 4H+
ionophore
The ETC
The Uncouplers
IMM
IMS
Matrix
I III IVII
4H+ 2H+ 4H+
No electrochemical
gradient formedNo ATP
formed
The ETC
Uncouplers
Ionophores:
2,4-Dinitrophenol - classic example
Valinomycin - allows K+ to pass through the IMM
Nigericin - allows K+ and H+ exchange
Dinitrocresol
Pentachlorophenol
Salicylanilides
CCCP
Bilirubin [B1], free fatty acid, thyroxine [T4]
The Uncouplers
The ETC
Oxidative Stress
Oxygen Reactive Oxygen Species (ROS)
[ O2-, H2O2, •OH, 1O2 ]
Drugs and
environmental
contaminantsOxidative damage:
Enzyme inactivation
Polysaccharide depolymerization
DNA breakage
Membrane destruction
A. Formation of reactive intermediates from molecular oxygen
B. Action of antioxidant enzymes
Lippincott’s Illustrated Biochemistry 4th Ed.
Oxidative Stress
Antioxidant Enzyme Systems
Superoxide dismutases (SOD)- copper and zinc containing
-
Antioxidant Enzyme Systems
Catalase - heme-containing enzyme
Oxidative Stress
Antioxidant Enzyme Systems
Glutathione peroxidase - selenium-containing
Oxidative Stress
NATURAL ANTI-OXIDANTS
Selenium
Iron
Copper Zinc
2H+ H+ H+
e- e- e- e-