Cellular Respiration and Fermentation[1]

8/4/2019 Cellular Respiration and Fermentation[1]

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LECTURE PRESEN TATIONS

For CAMPBELL BIOLOGY, NINTH EDITIONJane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

2011 Pearson Education, Inc.

Lectures by

Erin Barley

Kathleen Fitzpatrick

Cellular Respiration and

Fermentation

Chapter 9Overview: Life Is Work

Living cells require energy from outsidesources

Some animals, such as the chimpanzee, obtainenergy by eating plants, and some animals

feed on other organisms that eat plants


Figure 9.1

Energy flows into an ecosystem as sunlightand leaves as heat

Photosynthesis generates O2 and organic

molecules, which are used in cellular

respiration

Cells use chemical energy stored in organicmolecules to regenerate ATP, which powerswork


Figure 9.2

Lightenergy

ECOSYSTEM

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

CO2 H2O O2Organic

molecules

ATP powersmost cellular work

ATP

Heatenergy

Concept 9.1: Catabolic pathways yield

energy by oxidizing organic fuels

Several processes are central to cellularrespiration and related pathways



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Catabolic Pathways and Production of ATP

The breakdown of organic molecules isexergonic

Fermentation is a partial degradation ofsugars that occurs without O2

Aerobic respiration consumes organicmolecules and O2 and yields ATP

Anaerobic respiration is similar to aerobicrespiration but consumes compounds otherthan O2


Cellular respiration includes both aerobic andanaerobic respiration but is often used to referto aerobic respiration

Although carbohydrates, fats, and proteins are

all consumed as fuel, it is helpful to tracecellular respiration with the sugar glucose

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy(ATP + heat)


Redox Reactions: Oxidation and Reduction

The transfer of electrons during chemicalreactions releases energy stored in organicmolecules

This released energy is ultimately used to

synthesize ATP


The Principle of Redox

Chemical reactions that transfer electronsbetween reactants are called oxidation-reductionreactions, or redox reactions

In oxidation, a substance loses electrons, or isoxidized

In reduction, a substance gains electrons, or isreduced (the amount of positive charge isreduced)


Figure 9.UN01

becomes oxidized(loses electron)

becomes reduced(gains electron)

Figure 9.UN02

becomes oxidized

becomes reduced


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The electron donor is called the reducingagent

The electron receptor is called the oxidizingagent

Some redox reactions do not transfer electronsbut change the electron sharing in covalentbonds

An example is the reaction between methaneand O2


Figure 9.3

Reactants Products

Energy

WaterCarbon dioxideMethane(reducing

agent)

Oxygen(oxidizing

agent)

becomes oxidized

becomes reduced

Oxidation of Organic Fuel Molecules During

Cellular Respiration

During cellular respiration, the fuel (such asglucose) is oxidized, and O2 is reduced


Figure 9.UN03

becomes oxidized

becomes reduced

Stepwise Energy Harvest via NAD+ and the

Electron Transport Chain

In cellular respiration, glucose and other organicmolecules are broken down in a series of steps

Electrons from organic compounds are usuallyfirst transferred to NAD+, a coenzyme

As an electron acceptor, NAD+ functions as anoxidizing agent during cellular respiration

Each NADH (the reduced form of NAD+)represents stored energy that is tapped to

synthesize ATP


Figure 9.4

Nicotinamide(oxidized form)

NAD

(from food)

Dehydrogenase

Reduction of NAD

Oxidation of NADH

Nicotinamide(reduced form)

NADH


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Figure 9.UN04

Dehydrogenase

NADH passes the electrons to the electrontransport chain

Unlike an uncontrolled reaction, the electrontransport chain passes electrons in a series of

steps instead of one explosive reaction

O2 pulls electrons down the chain in an energy-yielding tumble

The energy yielded is used to regenerate ATP


Figure 9.5

(a) Uncontrolled reaction (b) Cellular respiration

Explosiverelease of

heat and lightenergy

Controlledrelease ofenergy for

synthesis ofATP

Freeenergy,

G

Freeenergy,

G

H2 1/2 O2 2 H 1/2 O2

1/2 O2

H2O

H2O

2 H+ 2 e

2 e

2 H+

ATP

ATP

ATP

(from food via NADH)

The Stages of Cellular Respiration:

A Preview

Harvesting of energy from glucose has threestages

Glycolysis (breaks down glucose into twomolecules of pyruvate)

The citric acid cycle (completes thebreakdown of glucose)

Oxidative phosphorylation (accounts for

most of the ATP synthesis)


Figure 9.UN05

Glycolysis (color-coded teal throughout the chapter)1.

Pyruvate oxidation and the citric acid cycle

(color-coded salmon)

2.

Oxidative phosphorylation: electron transport and

chemiosmosis (color-coded violet)

3.

Figure 9.6-1

Electronscarried

via NADH

Glycolysis

Glucose Pyruvate

CYTOSOL MITOCHONDRION

ATP

Substrate-levelphosphorylation


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Figure 9.6-2

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Pyruvateoxidation

Acetyl CoA

Glycolysis

Glucose Pyruvate


ATP ATP



Figure 9.6-3

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Pyruvateoxidation

Acetyl CoA

Glycolysis

Glucose Pyruvate

Oxidative

phosphorylation:electron transport

and

chemiosmosis


ATP ATP ATP



Oxidativephosphorylation

The process that generates most of the ATP iscalled oxidative phosphorylation because it ispowered by redox reactions


Oxidative phosphorylation accounts for almost90% of the ATP generated by cellularrespiration

A smaller amount of ATP is formed in glycolysis

and the citric acid cycle by substrate-levelphosphorylation

For each molecule of glucose degraded to CO2and water by respiration, the cell makes up to

32 molecules of ATP


Figure 9.7

Substrate

Product

ADP

P

ATP

Enzyme Enzyme

Concept 9.2: Glycolysis harvests chemical

energy by oxidizing glucose to pyruvate

Glycolysis (splitting of sugar) breaks downglucose into two molecules of pyruvate

Glycolysis occurs in the cytoplasm and has twomajor phases

Energy investment phase

Energy payoff phase

Glycolysis occurs whether or not O2 is present



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Figure 9.8

Energy Investment Phase

Glucose

2 ADP 2 P

4 ADP 4 PEnergy Payoff Phase

2 NAD+ 4 e 4 H+

2 Pyruvate 2 H2O

2 ATP used

4 ATP formed

2 NADH 2 H+

NetGlucose 2 Pyruvate 2 H2O

2 ATP

2 NADH 2 H+2 NAD+ 4 e 4 H+

4 ATP formed 2 ATP used

Figure 9.9-1

Glycolysis: Energy Investment Phase

ATPGlucose Glucose 6-phosphate

ADP

Hexokinase

1

Figure 9.9-2


ATPGlucose Glucose 6-phosphate Fructose 6-phosphate

ADP

Hexokinase Phosphogluco-isomerase

12

Figure 9.9-3


ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate

ADP ADP


Phospho-fructokinase

12 3

Figure 9.9-4


ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Tostep 6

ADP ADP



Aldolase

Isomerase

12 3 4

5

Figure 9.9-5

Glycolysis: Energy Payoff Phase

2 NADH

2 NAD +2 H

2 P i

1,3-Bisphospho-glycerate6

Triosephosphate

dehydrogenase


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Figure 9.9-6


2 ATP2 NADH

2 NAD +2 H

2 P i

2 ADP

1,3-Bisphospho-glycerate

3-Phospho-glycerate

2

Phospho-glycerokinase

67

Triosephosphate

dehydrogenase

Figure 9.9-7


2 ATP2 NADH

2 NAD +2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

2 2


Phospho-glyceromutase

67 8

Triosephosphate

dehydrogenase

Figure 9.9-8


2 ATP2 NADH

2 NAD +2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

Phosphoenol-pyruvate (PEP)

2 2 2

2 H2O



Enolase

67 8

9

Triosephosphate

dehydrogenase

Figure 9.9-9


2 ATP 2 ATP

2 NADH

2 NAD +2 H

2 P i

2 ADP


3-Phospho-glycerate

2-Phospho-glycerate

Phosphoenol-pyruvate (PEP)

Pyruvate

2 ADP2 2 2

2 H2O



Enolase Pyruvatekinase

67 8

910

Triosephosphate

dehydrogenase

Figure 9.9a


ATPGlucose Glucose 6-phosphate

ADP

Hexokinase

1

Fructose 6-phosphate

Phosphogluco-isomerase

2

Figure 9.9b


ATPFructose 6-phosphate

ADP

3

Fructose 1,6-bisphosphate


4

5

Aldolase

Dihydroxyacetonephosphate

Glyceraldehyde3-phosphate

Tostep 6

Isomerase


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Figure 9.9c


2 NADH2 ATP

2 ADP 2

2

2 NAD +2 H

2 P i

3-Phospho-glycerate


Triose

phosphatedehydrogenase


67

Figure 9.9d


2 ATP

2 ADP 2222

2 H2O

PyruvatePhosphoenol-pyruvate (PEP)

2-Phospho-glycerate

3-Phospho-glycerate

89

10


Enolase Pyruvatekinase

Concept 9.3: After pyruvate is oxidized, the

citric acid cycle completes the energy-

yielding oxidation of organic molecules

In the presence of O2, pyruvate enters themitochondrion (in eukaryotic cells) where theoxidation of glucose is completed


Oxidation of Pyruvate to Acetyl CoA

Before the citric acid cycle can begin, pyruvatemust be converted to acetyl Coenzyme A(acetyl CoA), which links glycolysis to the citric

acid cycle

This step is carried out by a multienzymecomplex that catalyses three reactions


Figure 9.10

Pyruvate

Transport protein

CYTOSOL

MITOCHONDRION

CO2 Coenzyme A

NAD + HNADH Acetyl CoA

1

2

3

The citric acid cycle, also called the Krebs

cycle, completes the break down of pyrvate toCO2

The cycle oxidizes organic fuel derived from

pyruvate, generating 1 ATP, 3 NADH, and 1FADH2 per turn


The Citric Acid Cycle


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Figure 9.11

Pyruvate

NAD

NADH

+ H Acetyl CoA

CO2

CoA

CoA

CoA

2 CO2

ADP + P i

FADH2

FAD

ATP

3 NADH

3 NAD

Citricacidcycle

+ 3 H

The citric acid cycle has eight steps, eachcatalyzed by a specific enzyme

The acetyl group of acetyl CoA joins the cycleby combining with oxaloacetate, forming citrate

The next seven steps decompose the citrateback to oxaloacetate, making the process acycle

The NADH and FADH2 produced by the cycle

relay electrons extracted from food to theelectron transport chain


Figure 9.12-1

1

Acetyl CoA

Citrate

Citricacidcycle

CoA-SH

Oxaloacetate

Figure 9.12-2

1

Acetyl CoA

CitrateIsocitrate

Citricacidcycle

H2O

2

CoA-SH

Oxaloacetate

Figure 9.12-3

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

Citric

acidcycle

NADH

+ H

NAD

H2O

3

2

CoA-SH

CO2

Oxaloacetate

Figure 9.12-4

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

Succinyl

CoA

Citric

acidcycle

NADH

NADH

+ H

+ H

NAD

NAD

H2O

3

2

4

CoA-SH

CO2

CoA-SH

CO2

Oxaloacetate


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1

Figure 9.12-5

1

Acetyl CoA

Citrate Isocitrate

-Ketoglutarate

Succinyl

CoA

Succinate

Citricacidcycle

NADH

NADH

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDP

P i

3

2

4

5

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12-6

1

Acetyl CoA

Citrate Isocitrate

-Ketoglutarate

Succinyl

CoA

Succinate

Fumarate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12-7

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

Succinyl

CoA

Succinate

Fumarate

Malate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

7

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12-8

NADH

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

Succinyl

CoA

Succinate

Fumarate

Malate

Citricacidcycle

NAD

NADH

NADH

FADH2

ATP

+ H

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDP

P i

FAD

3

2

4

5

6

7

8

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12a

Acetyl CoA

Oxaloacetate

CitrateIsocitrate

H2O

CoA-SH

1

2

Figure 9.12b

Isocitrate

-Ketoglutarate

SuccinylCoA

NADH

NADH

NAD

NAD

+ H

CoA-SH

CO2

CO2

3

4

+ H


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Figure 9.12c

Fumarate

FADH2

CoA-SH6

Succinate

SuccinylCoA

FAD

ADP

GTP GDP

P i

ATP

5

Figure 9.12d

Oxaloacetate8

Malate

Fumarate

H2O

NADH

NAD

+ H

7

Concept 9.4: During oxidative

phosphorylation, chemiosmosis couples

electron transport to ATP synthesis

Following glycolysis and the citric acid cycle,NADH and FADH2 account for most of theenergy extracted from food

These two electron carriers donate electrons to

the electron transport chain, which powers ATPsynthesis via oxidative phosphorylation


The Pathway of Electron Transport

The electron transport chain is in the innermembrane (cristae) of the mitochondrion

Most of the chains components are proteins,

which exist in multiprotein complexes

The carriers alternate reduced and oxidizedstates as they accept and donate electrons

Electrons drop in free energy as they go downthe chain and are finally passed to O2, forming

H2O


Figure 9.13

NADH

FADH2

2 H + 1/2 O2

2 e

2 e

2 e

H2O

NAD

Multiproteincomplexes

(originally fromNADH or FADH2)

III

III

IV

50

40

30

20

10

0

Freeenergy(G)relativetoO2

(kcal/mol)

FMN

FeS FeS

FAD

QCyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

FeS

Electrons are transferred from NADH or FADH2

to the electron transport chain Electrons are passed through a number of

proteins including cytochromes (each with an

iron atom) to O2

The electron transport chain generates no ATPdirectly

It breaks the large free-energy drop from foodto O2 into smaller steps that release energy inmanageable amounts



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Chemiosmosis: The Energy-Coupling

Mechanism

Electron transfer in the electron transport chain

causes proteins to pump H+

from themitochondrial matrix to the intermembrane space

H+ then moves back across the membrane,

passing through the proton, ATP synthase

ATP synthase uses the exergonic flow of H+ todrive phosphorylation of ATP

This is an example of chemiosmosis, the use ofenergy in a H+ gradient to drive cellular work


Figure 9.14

INTERMEMBRANE SPACE

Rotor

StatorH

Internalrod

Catalyticknob

ADP+

P i ATP

MITOCHONDRIAL MATRIX

Figure 9.15

Proteincomplexof electroncarriers

(carrying electronsfrom food)

Electron transport chain

Oxidative phosphorylation

Chemiosmosis

ATPsynth-ase

I

II

III

IVQ

Cyt c

FADFADH2

NADH ADP P iNAD

H

2 H + 1/2O2

H

HH

21

H

H2O

ATP

The energy stored in a H+ gradient across amembrane couples the redox reactions of theelectron transport chain to ATP synthesis

The H+ gradient is referred to as a proton-

motive force, emphasizing its capacity to dowork


An Accounting of ATP Production by

Cellular Respiration

During cellular respiration, most energy flowsin this sequence:

glucose NADH electron transport chain

proton-motive force ATP

About 34% of the energy in a glucose moleculeis transferred to ATP during cellular respiration,making about 32 ATP

There are several reasons why the number ofATP is not known exactly


Figure 9.16

Electron shuttlesspan membrane

MITOCHONDRION2 NADH

2 NADH 2 NADH 6 NADH

2 FADH2

2 FADH2

or

2 ATP2 ATP about 26 or 28 ATP

Glycolysis

Glucose 2 Pyruvate

Pyruvate oxidation

2 Acetyl CoA

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

CYTOSOL

Maximum per glucose:About

30 or 32 ATP


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1

Concept 9.5: Fermentation and anaerobic

respiration enable cells to produce ATP

without the use of oxygen

Most cellular respiration requires O2 to produceATP

Without O2, the electron transport chain willcease to operate

In that case, glycolysis couples withfermentation or anaerobic respiration to

produce ATP


Anaerobic respiration uses an electrontransport chain with a final electron acceptorother than O

2, for example sulfate

Fermentation uses substrate-level

phosphorylation instead of an electrontransport chain to generate ATP


Types of Fermentation

Fermentation consists of glycolysis plusreactions that regenerate NAD+, which can bereused by glycolysis

Two common types are alcohol fermentation

and lactic acid fermentation


In alcohol fermentation, pyruvate is convertedto ethanol in two steps, with the first releasingCO2

Alcohol fermentation by yeast is used in

brewing, winemaking, and baking



Animation: Fermentation OverviewRight-click slide / select Play

Figure 9.17

2 ADP 2 ATP

Glucose Glycolysis

2 Pyruvate

2 CO22

2 NADH

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation (b) Lactic acid fermentation

2 Lactate

2 Pyruvate

2 NADH

Glucose Glycolysis

2 ATP2 ADP2 Pi

NAD

2 H

2 Pi

2 NAD2 H


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2 ADP 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 CO22 NAD

2 NADH

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation

2 H

Figure 9.17a

In lactic acid fermentation, pyruvate is reducedto NADH, forming lactate as an end product,with no release of CO

2

Lactic acid fermentation by some fungi and

bacteria is used to make cheese and yogurt

Human muscle cells use lactic acidfermentation to generate ATP when O2 isscarce


(b) Lactic acid fermentation

2 Lactate

2 Pyruvate

2 NADH

Glucose Glycolysis

2 ADP 2 P i 2 ATP

2 NAD

2 H

Figure 9.17b

Comparing Fermentation with Anaerobic

and Aerobic Respiration

All use glycolysis (net ATP =2) to oxidize glucoseand harvest chemical energy of food

In all three, NAD+ is the oxidizing agent thataccepts electrons during glycolysis

The processes have different final electronacceptors: an organic molecule (such as pyruvateor acetaldehyde) in fermentation and O2 in cellularrespiration

Cellular respiration produces 32 ATP per glucosemolecule; fermentation produces 2 ATP perglucose molecule


Obligate anaerobes carry out fermentation or

anaerobic respiration and cannot survive in thepresence of O2

Yeast and many bacteria are facultative

anaerobes, meaning that they can surviveusing either fermentation or cellular respiration

In a facultative anaerobe, pyruvate is a fork in

the metabolic road that leads to two alternativecatabolic routes


Figure 9.18

Glucose

CYTOSOLGlycolysis

Pyruvate

No O2 present:Fermentation

O2 present:Aerobic cellular

respiration

Ethanol,

lactate, orother products

Acetyl CoA

MITOCHONDRION

Citricacidcycle


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The Evolutionary Significance of Glycolysis

Ancient prokaryotes are thought to have usedglycolysis long before there was oxygen in theatmosphere

Very little O2 was available in the atmosphere

until about 2.7 billion years ago, so earlyprokaryotes likely used only glycolysis togenerate ATP

Glycolysis is a very ancient process


Concept 9.6: Glycolysis and the citric acid

cycle connect to many other metabolic

pathways

Gycolysis and the citric acid cycle are majorintersections to various catabolic and anabolicpathways


The Versatility of Catabolism

Catabolic pathways funnel electrons from manykinds of organic molecules into cellularrespiration

Glycolysis accepts a wide range of

carbohydrates

Proteins must be digested to amino acids;amino groups can feed glycolysis or the citricacid cycle


Fats are digested to glycerol (used inglycolysis) and fatty acids (used in generatingacetyl CoA)

Fatty acids are broken down by beta oxidation

and yield acetyl CoA

An oxidized gram of fat produces more thantwice as much ATP as an oxidized gram ofcarbohydrate


Figure 9.19

CarbohydratesProteins

Fattyacids

Amino

acids

Sugars

Fats

Glycerol

Glycolysis

Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

Acetyl CoA

Citricacidcycle

Oxidativephosphorylation

Biosynthesis (Anabolic Pathways)

The body uses small molecules to build other

substances These small molecules may come directly

from food, from glycolysis, or from the citric

acid cycle



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Regulation of Cellular Respiration via

Feedback Mechanisms

Feedback inhibition is the most common

mechanism for control If ATP concentration begins to drop,

respiration speeds up; when there is plenty

of ATP, respiration slows down

Control of catabolism is based mainly onregulating the activity of enzymes atstrategic points in the catabolic pathway


Figure 9.20

Phosphofructokinase

Glucose

GlycolysisAMP

Stimulates

Fructose 6-phosphate

Fructose 1,6-bisphosphate

Pyruvate

Inhibits Inhibits

ATP Citrate

Citric

acid

cycle

Oxidative

phosphorylation

Acetyl CoA

Figure 9.UN06

Inputs Outputs

Glucose

Glycolysis

2 Pyruvate 2 ATP 2 NADH

Figure 9.UN07

Inputs Outputs

2 Pyruvate 2 Acetyl CoA

2 OxaloacetateCitricacidcycle

2

26

8ATP NADH

FADH2CO2

Figure 9.UN08

Protein complexof electroncarriers

(carrying electrons from food)

INTERMEMBRANESPACE

MITOCHONDRIAL MATRIX

H

HH

2 H+ 1/2 O2 H2O

NAD

FADH2 FAD

Q

NADH

I

II

III

IV

Cyt c

Figure 9.UN09

INTER-MEMBRANESPACE

HADP + P i

MITO-CHONDRIALMATRIX

ATPsynthase

H

ATP

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Cellular Respiration and Fermentation[1]