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Electron Transport Chain

Filename: ETChain.ppt

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Lecture Outline

• Using Chemical energy to drive metabolism• Production of ATP• Cellular respiration

– Clycolysis– Krebs cycle– Electron transport – Chemiosmosis

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Lecture Overview

• All organisms drive their metabolism with ATP generated from

• Rearrangement of chemical bonds • Energetic electrons from proton pumps• Electrons from photosynthesis • Electrons from oxidation of sugars and fats

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Cellular Respiration

• Release of energy stored in organic compounds

– Carbohydrate– Fats– Proteins (net energy loss)

• Oxygen is consumed as a reactant• Carbon dioxide and water are byproducts• Energy is used indirectly

– trapped as ATP

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Pathways in Cellular Respiration

• Glycolysis• Krebs cycle• Electron transport chain

Cellular RespirationCumulative function of three

metabolic pathways and chemiosmosis

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Catabolism of various foods

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Overview of Cellular RespirationA room of your own...

ATP ATPATP

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Electron Transport

System

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Summary of Krebs Cycle

IN

IN

IN

IN

Out

Out

Out

Out

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Electron Transport Chain• OCCURS in MITOCHONDRIAL INNER

MEMBRANE or PROKARYTOIC CELL MEMBRANE

• linked to Glycolysis and Krebs cycle • Electrons passed from NADH to oxygen• Does not make ATP directly but through

chemiosmosisLarge Free energy drop ( 53 kcal/mol) is broken

into a series of smaller steps that release energy in manageable amounts

Oxidation is the loss of electrons to any electron acceptor

Although oxygen is the usual electron acceptor

other electron acceptors include NAD+

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ReductionNADH

Nicotinamide-adenine dinucleotide

Oxidation

NADH as an Electron Shuttle

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Electron Transport

Chain

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ATP

How ATP Drives Cellular Work

ATP

ATP

ATP

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2 Ways to Produce ATP

• Substrate level phosphorylation– produces few molecules of ATP in aerobes (2

ATP from the respiration of 1 molecule of glucose)

• Proton motor force (chemiosmosis)– produces most of the ATP in aerobes (about 30

ATP from the complete respiration of glucose to CO2 and H2O)

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Substrate Level Phosphorylation ATP Production

• more primitive methodExamples: 2 steps in glycolysis where

• ADP + Substrate-P -> ATP + substrate

• Note that the phosphate comes from a phosphorylated substrate, not from Pi

• 2 ADP + Phosphoenolpyruvate -> pyruvate + 2 ATP

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Proton Motor ForceATP production

ATP synthase/ FoF1 complex

• More advanced method

• Proton transport across a membrane with FoF1 complex powers the following reaction:-

• ADP + Pi -> ATP

• Note that the phosphate comes from Pi

(inorganic phosphate)

• This is the major ATP source for aerobic bacteria, mitochondria and chloroplasts

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ATP synthase/ FoF1 complex requires:

• Membrane

• Gradient of H+ concentration across membrane (one side more acid than the other)

• Fo/Fi protein complex in membrane

• ADP + Pi

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FoF1 complexFoF1 complex

low pH H+

H+

H+

H+ H

+

H+

H+

H+

H+H

+

ADP+Pi

ATP

Membrane Fo

F1

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FoF1 complexFoF1 complex

H+

H+

ADP ATP

H+

+Pi

H+

H+

Fo (3 subunits in bacteria) forms a proton channel

F1 (9 protein subunits) carries ATP synthase

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Fo

F1

Fo

F1

Fo

F1

FoF1 complexes under EM look FoF1 complexes under EM look like like ““lloolllliippooppss””

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Fo

F1 Shows only ATP’ase

H+

F1

F1

Fo Shows protontransfer

H+

H+

H+

Dissociated FoF1

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Aerobic bacterium

Chloroplast

Mitochondrion

stroma

matrix

thylakoid

= acid region

FOF1 COMPLEXES

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How does the FoF1 complex work?

Fo

F1?

One hypothesis is that F1 rotatesas it releases ATP’s

Not known

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chemical energy

proton motor force

ATP

Chemiosmosis

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Tally=2 Tally=0

Tally=2

Tally= ~36

Review