energy metabolism

94
Energy Metabolism MARI-ANN BENIGNO-BRINGAS, MD Department of Biochemistry & Nutrition FEU-NRMF Institute of Medicine

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Page 1: Energy metabolism

Energy Metabolism

MARI-ANN BENIGNO-BRINGAS, MD

Department of Biochemistry & Nutrition

FEU-NRMF Institute of Medicine

Page 3: Energy metabolism

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

Page 4: Energy metabolism

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

Page 5: 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

Page 6: 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

Page 8: Energy metabolism

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

Page 9: Energy metabolism

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

Page 10: Energy metabolism

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

Page 11: Energy metabolism

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

Page 12: Energy metabolism

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

Page 13: Energy metabolism

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

Page 14: Energy metabolism

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.

Page 15: Energy metabolism
Page 17: Energy metabolism
Page 18: Energy metabolism

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

Page 21: Energy metabolism

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

Page 22: Energy metabolism
Page 23: Energy metabolism

- co-factor: Mg++

- aka “energy currency of the cell”

[Lipmann Law]

~ PPP ~

The ATP

ATP [Adenosine triphosphate]

Page 24: Energy metabolism

~ 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

Page 25: Energy metabolism

The ATP

QUESTION:

Why is ADP + Pi more

stable than ATP?

Page 26: Energy metabolism

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

Page 27: Energy metabolism

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

Page 29: Energy metabolism

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

Page 30: Energy metabolism

Kreb’s Cycle Glycolysis

Page 31: Energy metabolism

Sources of ATP

The ATP

(2 ATPs)‏ (1 ATP)‏ (3 ATPs)‏

Page 32: Energy metabolism

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.

Page 33: Energy metabolism
Page 34: Energy metabolism

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 ”

Page 37: Energy metabolism

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)‏

Page 38: Energy metabolism

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

Page 40: Energy metabolism
Page 41: Energy metabolism
Page 43: Energy metabolism

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

Page 44: Energy metabolism

NAD/NADH + H+

Page 45: Energy metabolism

FAD/FADH2

Flavin adenine dinucleotide (FAD) is also a

biological oxidizing agent

Protons, as well as, electrons are accepted by

FAD

Page 46: Energy metabolism

The Structures of Riboflavin, Flavin Mono-nucleotide (FMN), and Flavin Dinucleotide (FAD)

Page 47: Energy metabolism

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

Page 48: Energy metabolism

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+

Page 49: Energy metabolism

Glycerol-3-phosphate Shuttle System

The ETC

Cytosol Matrix

NADH + H+

NAD+ DHAP

Glycerol-3-phosphate

ETC

FADH2

Page 50: Energy metabolism
Page 51: Energy metabolism

ATP

ATP

ATP

GLUCOSE

GLU-6-PO4

PYRUVATE

ACETYL COA

NADH

NADH

NADH

NADH

FADH2

KREBS

Page 52: Energy metabolism

The ETC

Components of the ETC

Page 53: Energy metabolism

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

Page 54: Energy metabolism

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

Page 55: Energy metabolism

The ETC

The Various ETC Complexes

NADH

FADH2

CoQ Cyt b, c1 Cyt c Cyt aa3

Complex I

NADH Coenzyme Q reductase

Page 56: Energy metabolism

The ETC

The Various ETC Complexes

NADH

FADH2

CoQ Cyt b, c1 Cyt c Cyt aa3

Complex II

Succinate Coenzyme Q reductase

Page 57: Energy metabolism

The ETC

The Various ETC Complexes

CoQ Cyt b, c1 Cyt c Cyt aa3

Complex III

Coenzyme Q-Cytochrome C reductase

NADH

FADH2

Page 58: Energy metabolism

The ETC

The Various ETC Complexes

NADH +H

FADH2

CoQ Cyt b, c1 Cyt c Cyt aa3

Complex IV

Cytochrome oxidase

Page 59: Energy metabolism

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

Page 61: Energy metabolism

The ETC

Sites of Proton Translocation

Page 62: Energy metabolism
Page 63: Energy metabolism

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

Page 64: Energy metabolism

The Chemiosmotic Theory

IMM

IMS

Matrix

I III IVII

Free energy

e- e-

The ETC

Page 65: Energy metabolism

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

Page 66: Energy metabolism

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

Page 67: Energy metabolism

The Chemiosmotic Theory

IMM

IMS

Matrix

I III IVII

4H+ 4H+ 2H+

proticity

ADP + Pi ATP

The ETC

Page 68: Energy metabolism
Page 69: Energy metabolism
Page 70: Energy metabolism

The Chemiosmotic Model

The ETC

Page 71: Energy metabolism

The Chemiosmotic Theory

IMM

IMS

Matrix

I III IVII

Fo

F1

Stalk (OSCP)‏

v

ATP Synthase

The ETC

Page 72: Energy metabolism

“Binding change” mechanism

IMM

IMS

Matrix

I III IVII

4H+ 4H+ 2H+

ADP + Pi(spontaneous)‏

ATP release

The ETC

3H+

Page 73: Energy metabolism

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

Page 74: Energy metabolism

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

Page 75: Energy metabolism

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.

Page 76: Energy metabolism

The Site-specific Inhibitors

IMM

IMS

Matrix

I III IVII

Carboxin

TTFA

Malonate

The ETC

systemic anilide fungicide.

Thenoyltrifluoroacetone –conventional complex II inhibitor

Page 77: Energy metabolism

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

Page 78: Energy metabolism

The Site-specific Inhibitors

IMM

IMS

Matrix

I III IVII

Cyanide

Hydrogen sulfide

Carbon monoxide

The ETC

Page 79: Energy metabolism

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

Page 80: Energy metabolism

ETC

The Uncouplers

IMM

IMS

Matrix

I III IVII

4H+ 2H+ 4H+

ionophore

The ETC

Page 81: Energy metabolism

The Uncouplers

IMM

IMS

Matrix

I III IVII

4H+ 2H+ 4H+

No electrochemical

gradient formedNo ATP

formed

The ETC

Page 82: Energy metabolism

Uncouplers

Page 83: Energy metabolism

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

Page 84: Energy metabolism
Page 85: Energy metabolism

Oxidative Stress

Oxygen Reactive Oxygen Species (ROS)‏

[ O2-, H2O2, •OH, 1O2 ]

Drugs and

environmental

contaminants‏Oxidative damage:

Enzyme inactivation

Polysaccharide depolymerization

DNA breakage

Membrane destruction

Page 86: Energy metabolism
Page 87: Energy metabolism
Page 88: Energy metabolism
Page 89: Energy metabolism

A. Formation of reactive intermediates from molecular oxygen

B. Action of antioxidant enzymes

Lippincott’s Illustrated Biochemistry 4th Ed.

Page 93: Energy metabolism

NATURAL ANTI-OXIDANTS

Selenium

Iron

Copper Zinc

2H+ H+ H+

e- e- e- e-