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BIOC 460 - DR. TISCHLER

LECTURE 25

OXIDATIVE PHOSPHORYLATION:

AN EXPLOSION OF ENERGY

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1. What effect does insulin have on glucose transport

increases by moving transporters to the membrane

2. Name one tissue where insulin controls glucose transport

muscle OR adipose.

3. Glucose increases insulin secretion by causing an increase in the cell

concentration of what molecule? Calcium

4. What vitamin is the precursor for NADH? Niacin

5. How is pyruvate kinase structurally modified after glucagon binds to the

liver cell? Phosphorylation

6. In the red cell, which lacks mitochondria, how is NAD for glycolysis

replenished to keep glycolysis going? Conversion to lactate or LDH

7. Identify an allosteric inhibitor of the phosphofructokinase -1 reaction.

ATP or citrate or H+

8. Identify an allosteric activator of the phosphofructokinase -1 reaction.

AMP or fructose-2,6-bisphosphate

Quiz 8

2

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OBJECTIVES

1. Distinguish between electroneutral and electrogenic transport;

describe the significance of electrogenic transport for the adeninenucleotide transporterand the role of this transporter.

2. Discuss oxidative phosphorylation in relation to the chemiosmotic

model.

3. Identify the components of the ATP synthase complex, and

describe their roles.

4. Explain how the malate-aspartate and the -glycerol phosphate

electron shuttlesgenerate energy from the NADH produced by

glycolysis. (Do not m emorize the layou t of the shutt le to reproduce

it but und erstand their key aspects)

5. Define respiratory controland uncoupling, and describe the

physiological importance of these processes.

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PHYSIOLOGICAL PREMISE

Why do some snake and spider venoms cause cell death at the site

of the bite in particular? Some of these venoms contain enzymes

called phospholipases. Phospholipases hydrolyze membrane

phospholipids to release fatty acids. Phospholipases in snake or

spider venom degrade phospholipids in the mitochondrialmembrane. The fatty acids released act as natural uncouplers that,

as is described in this lecture, prevent oxidative phosphorylation by

destroying the pH gradient. Consequently the cell dies because of

an inability to produce enough energy.

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MITOCHONDRIAL TRANSPORT SYSTEMS

Examples of Electroneutral Transport:

Pyruvate1-moves into matrix and OH1-moves out

Phosphate1-moves into matrix and OH1-moves out

Citrate3-

+ H+exchanges with malate

2-

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Adenine nucleotide

translocaseATP4-

ADP3-

Figure 1. Electrogenic transport system in mitochondria.

Inner

Membrane

Matrix

SideIntermembraneSpace

Electrogenic Transport

Net negative

charge

moves out

MITOCHONDRIAL TRANSPORT SYSTEMS

Aspartate

translocaseAsp1-

Glu1-+ H+

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4H+

INTERMEMBRANE SPACE

OH-

ATP4-

F1

Fo

3H+

MATRIXstalk

3H+

Proton gradient/

Charge gradient

FMNH2

4H+

complex I

CoQcyt b

complex III

C1

Ccyta-a3

2H+2H+

O2

e-

H2O

NADH

+ H+

inner

membraneNAD+

Pi-

e-

e-

e-

e-e-

e-

e-e-e-

4H+

4H+

complex IV

ADP3-

ATP4-

ATP4-

ATP4-

OH-

OH-

ADP3-

ADP3-

ADP3-

ADP3-

ADP3-

ADP3-

ADP3-

Figure 2. Oxidative Phosphorylation

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FEATURES OF THE CHEMIOSMOTIC MODEL:

mitochondrial inner membrane is impermeableto protons

by simple diffusion

measurable proton (pH) gradient exists across the inner

membrane

collapse of the proton gradient (uncoupling) abolishes

ATP synthesis but accelerates O2consumption

inhibition of the respiratory chain prevents ATP synthesis

because pumping of protons ceases

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OAA

Malate

(1)

e-

NAD+

e-Glu0

(6)

CYTOPLASM

e= electrons

OUTER

MEMBRANE

MATRIX

Glu0

Asp-1 (4)

INNER

MEMBRANE

KG KG

Malate(2) e-

e-

OAA NADH

NAD+

(3)

e-

Complex I

e-NAD+

Glucose

Pyruvate

GLYCOLYSIS

NADH

Figure 3. The malate-aspartate shuttle.

Asp-1(5)

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e= electrons

CYTOPLASM

INNER

MEMBRANE

MATRIX

FAD

Glycerol-3-phosphate

dehydrogenase

(2)

DHAP

G3P

Dihydroxyacetone

phosphate(DHAP)

NAD+ 3-phosphateGlycerol

e

(1)

FADH2

e

CoQe

O2

eOUTER

MEMBRANE

Figure 4. Glycerol phosphate shuttle. Cytoplasmic glycerol 3-

phosphate dehydrogenase (1) oxidizes NADH. Glycerol 3-phosphate

dehydrogenase in the inner membrane (2) reduces FAD to FADH2.

NADH

Glucose

Pyruvate

GLYCOLYSISNAD+

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RESPIRATORY CONTROL

depends on the availability of ADP

increased ADP in matrix opens proton channel

protons move through channel down pH gradient

respiration increases to compensate for decline in pH

gradient; oxygen consumption (respiration) controlledat low ADP, ATP synthesis ceases, pH gradient builds up,

oxygen use diminishes

as ATP needs rise (i.e., ADP increases) respiration is again

accelerated

inhibition of respiratory chain causes loss of control

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UNCOUPLER EFFECTS

hydrophobic molecules that bind protons

take protons into matrix to collapse pH gradient

without pH gradient, synthesis of ATP ceases

electron transport chain operates at high rate; protons are

pumped out rapidly in attempt to restore pH gradient

energy is released as heat and the body temperature rises

respiratory control is lost

uncoupled brown fat mitochondria generates body heat in

infants until shivering reflex develops

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ALANINE

+ nitrogen

GLYCOGEN

CYTOPLASM

INTERMEMBRANE

SPACE

LACTATE

NADH

MITOCHONDRIAL

MATRIX

H+

ATP

ADP+ Pi

ATPADP

Pi

NADH

MALATE-ASP

SHUTTLE

PYRUVATE

GLUCOSE

PYRUVATE

ACETYL CoAPDH

PC

TCA CYCLE

SDH

complex I

NADH

NAD

complex III

complex IVCS

KgDH

MDH

H+

OaaMal

ICDH

H+

Fig. 5 Effects of uncoupling on glucose,

lactate and mitochondrial metabolism

uncoupler

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Medical Scenario I:

As a current medical student and a former lawyer you become interested

in what could have been a lucrative malpractice case in the 1920's. At

that time, some physicians, without the benefit of modern biochemistry

knowledge, prescribed dinitrophenol as a weight-reducing agent. For

some patients it worked satisfactorily, the only side effects being

sweating and a slight elevation in temperature. However, in patients who

were more overweight and required long-term treatments, their bodytemperature increased to such an extent that death resulted. Associated

with their condition was a marked increase in their rate of respiration and

an inability to gain weight even with increased caloric intake.

Medical Scenario II:

During World War II workers in munitions factories were exposed to a

chemical called trinitrophenol. A common occurrence in these workers

was frequent absenteeism due to elevated temperature, weakness and

accelerated breathing that improved after several days at home. What

would you have recommended to reduce the incidence of such illness?