7.1 Overview of Cellular · PDF file8/30/2013 3 7 Phases of Cellular Respiration • Glycolysis is the breakdown of glucose into two molecules of pyruvate. – Oxidation by removal

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7.1 Overview of Cellular

Respiration• Cellular respiration is the release of energy from

molecules such as glucose accompanied by the

use of this energy to synthesize ATP molecules.

– Aerobic – requires O2

– Gives off CO2

ATP36-38P

glucose water

C6H12O6 + 6O2

oxygen

6CO2 + 6H2O

ADP +

carbondioxide


3

7.1 Overview of Cellular

Respiration

• Glucose is a high-energy molecule, and as it is broken down, energy is released.

• This energy used to produce ATP.

• The breakdown of one glucose molecule

results in 36 or 38 ATP molecules.

• The pathways of cellular respiration allow the

energy within a glucose molecule to be released slowly for ATP synthesis.

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4

NAD+ and FAD

• Cellular respiration involves many individual

reactions, each requiring its own enzyme.

– Certain enzymes utilize two coenzymes.

• NAD+ (nicotinamide adenine dinucleotide)

• FAD (flavin adenine dinucleotide)

– Each carries two electrons and two hydrogen

atoms.

– They pick up electrons at specific enzymatic

reactions and carry these electrons to the electron

transport chain.

5


NAD+

2H

oxidationreduction

2H

2e– + 2H+

NADH + H+

2e– + 2H+

Figure 7.1

6

Phases of Cellular Respiration

• Phases of Cellular Respiration

– Glycolysis

– Preparatory Reaction

– Citric Acid Cycle

– Electron Transport Chain

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• Glycolysis is the breakdown of glucose

into two molecules of pyruvate.

– Oxidation by removal of electrons (e-) and hydrogen ions (H+) provides the energy for the immediate buildup of two ATP.

8


• Preparatory (Prep) Reaction

– Pyruvate is oxidized to acetyl CoA and carbon

dioxide is removed

– One three-carbon molecule becomes one two-carbon molecule.

– Prep reaction occurs twice because glycolysis produces two pyruvates.

9


• Citric Acid Cycle

– Cyclical series of oxidation reactions that

produce one ATP and carbon dioxide per turn

• Acetyl CoA is converted to citric acid and enters the cycle.

• Citric acid cycle turns twice because two acetyl CoA’s are produced per glucose.

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• Electron Transport Chain

– Series of electron carrier molecules

• Electrons are passed from one carrier to another.

• As the electrons move from a higher energy state to a lower one, energy is released to make ATP.

• Under aerobic conditions 32-34 ATP per glucose molecule can be produced.

11

e–

ATP

energy for

synthesis of

e–

electron

transport chain

high-energy

electrons

low-energy

electrons


Figure 7.3

12Figure 7.2


22

e–

e–

e–

e– Mitochondrion

2 ATP

2 ADP

4 ATP total4 ADP

ATP net gain 2 ADP ATP 32 or 34 ADP 32 or 34 ATP

pyruvateglucose

Glycolysis

Cytoplasm

Preparatory reaction Citric acidcycle

Electron transportchain and

chemiosmosis

e–

e–

NADH

NADH

NADH andFADH2

e–

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• Pyruvate

– Pivotal metabolite in cellular respiration

• If no oxygen is available, pyruvate is reduced to

lactate (in animals) or alcohol and carbon dioxide (in

plants) in a process called fermentation.

• Fermentation results in a net gain of two

ATP/glucose.

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7.2 Outside the Mitochondria:

Glycolysis

• Glycolysis is the breakdown of glucose

to two molecules of pyruvate.

– Takes place in the cytoplasm

– Does not require oxygen

– Transforms one 6-carbon molecule into two

3-carbon molecules

15


Glycolysis• Energy Investment Steps

– Two molecules of ATP used to activate

glucose as glycolysis begins

• Energy Harvesting Steps

– Oxidation of G3P results in NADH synthesis

– Additional chemical changes lead to direct

substrate-level phosphorylation, formation of 4 ATP

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22

e–

e–

e–

e– Mitochondrion

2 ATP

2 ADP

4 ATP total4 ADP

ATP net gain 2 ADP ATP 32 or 34 ADP 32 or 34 ATP

pyruvateglucose

Glycolysis

Cytoplasm

Preparatory reaction Citric acidcycle


chemiosmosis

e–

e–

NADH

NADH

NADH andFADH2

e–

17

Inputs and Outputs of Glycolysis


Glycolysis

outputsinputs

2 NAD+

2 ATP

P

2 ATP Net gain

totalATP

2 (3C) pyruvate

NADH

ADP2

2

4

6C glucose

4ADP + 4

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ADPADP

StepsEnergy-Investment Steps

- 2 ATPATP ATP 1. Two ATP are used

to activate glucose.

glucose

PP

Figure 7.4

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ADPADP

StepsEnergy-Investment Steps

- 2 ATPATP ATP 1. Two ATP are used


2. A resulting C6 molecule breaksdown into 2 C3 molecules.

glucose

P

G3P

P

G3P

PP

Figure 7.4

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glucose

PP

ADPADP

Steps

NAD+NAD+

PP

P

P P

P

NADH + H+

P P

Energy-Investment Steps

- 2

NADH + H+

Energy-Harvesting Steps

ATPATP ATP 1. Two ATP are used



3. NAD+ takes an electronbecoming NADH + H+, withaddition of a second phosphateto the sugar.

BPGBPG

G3P G3P

Figure 7.4

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glucose

PP

ADPADP

Steps

+ 2

NAD+

3PG3PG

NAD+

PP

P

P P

ADPADP

P

NADH + H+

P P

P P


- 2

ATP

ATP ATP

NADH + H+






4. Removal of high-energyphosphate from 2 BPG by 2 ADPproduces 2 ATP and 2 3PGmolecules.

BPGBPG

G3P G3P

Figure 7.4

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glucose

PP

ADPADP

Steps

+ 2

NAD+NAD+

PP

P

P P

ADPADP

P

H2O

P

NADH + H+

P P

P

P P


- 2

H2O

ATP

ATP ATP

NADH + H+






4. Removal of high-energyphosphate from 2 BPG by 2 ADPproduces 2 ATP and 2 3PGmolecules.

5. Oxidation of 2 3PG by removalof water results in 2 high-energyPEP molecules.

BPG

3PG

PEP

BPG

3PG

PEP

G3P G3P

Figure 7.4

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PP

ADPADP

Steps

ATP+ 2

+ 2

(net gain)2

NAD+NAD+

PP

P

P P

ADPADP

P

ADP

H2O

ADP

P

NADH + H+

P P

P

P P

b.


- 2

H2O

ATP

ATP

ATP

ATP

ATP

ATP

NADH + H+




2. A resulting C6 molecule breaks

down into 2 C3 molecules.

3. NAD+ takes an electron

becoming NADH + H+, with

addition of a second phosphateto the sugar.

4. Removal of high-energy

phosphate from 2 BPG by 2 ADP

produces 2 ATP and 2 3PGmolecules.

6. Removal of high-energy

phosphate from 2 PEP by 2

ADP produces 2 ATP and 2pyruvate molecules.

5. Oxidation of 2 3PG by removal

of water results in 2 high-energy

PEP molecules.

glucose

G3P G3P

BPGBPG

3PG3PG

PEPPEP

pyruvate pyruvate

Figure 7.4

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Fermentation

• If O2 is limited, cells may utilize anaerobic pathways, such as fermentation.

• In animal cells, pyruvate from glycolysis accepts two hydrogen ions and two electrons and is reduced to lactate.

• Yeast generates ethyl alcohol and CO2 by fermentation.

• Two NADH pass electrons to pyruvate to reduce it to lactate.

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Advantages and Disadvantages of Fermentation

• Fermentation is essential to humans since it can provide a rapid burst of ATP.

• In muscles working vigorously over a short period, fermentation is used to produce ATP as

O2 is in limited supply.

• Lactate is toxic to cells.

• As it accumulates, lactate changes the pH of the muscle cells, causing the “burn” feeling.

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Energy Yield of Fermentation

• Fermentation yields only two ATP by substrate-level ATP synthesis.

• These two ATP represent a small fraction of potential energy stored in glucose.

• In cellular respiration, 36 to 38 ATP molecules produced.

• Therefore, most of the potential energy stored in glucose has not been released.

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inputs outputs

glucose

4 ADP + 2 P

ATP2

ATP2

ATP4

Fermentation

2 lactate or

2 alcohol and 2 CO2

2 ADP

net gain


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28Figure 7.5

+4 4

2

glucose

ATP–2

ATP

ATP

E1

2 ADP

2 NAD+

G3P

BPG

pyruvate

4 ADP

E2

2 P

P

2 alcohol2 lactate

2

E4

2

2

2

(net gain)

or

2 CO2

or

ATPE3

ATP

NADH2

Animalsand bacteria

Plantsand yeast


29

Preparatory Reaction

• Preparatory Reaction

– Produces the molecule that will enter the citric

acid cycle.

• Reaction occurs in the cristae of mitochondria.

• Cristae are folds of the inner membrane that jut out into the matrix.

• 3C pyruvate is converted to 2C acetyl group.

30

Preparatory Reaction

– Acetyl group attached to CoA to become acteyl CoA

– Carbon dioxide is produced.

– Hydrogen atoms are removed from pyruvate and picked up to form NADH + H+.

– This reaction occurs twice per glucose.Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

2 acetyl—CoA + 2 carbon dioxide2 pyruvate + 2 CoA

2 NADH + H+2 NAD+

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Citric Acid Cycle

• Citric Acid Cycle

– Cyclical pathway that occurs in the matrix of

mitochondria

• A two-carbon acetyl group of Acetyl CoA combines with

a C4 molecule (oxaloacetate) to produce C6 citrate.

• The CoA is recycled to the preparatory reaction.

32

Citric Acid Cycle

– Each two-carbon acetyl group is oxidized to two CO2 molecules.

– Reactions produce three NADH + H+ and one

FADH2 .

– One ATP is produced by substrate-level ATP synthesis.

– Cycle turns twice per original glucose molecule.

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inputs outputs

6 NAD+

2 ADP + 2 PATP2

Citric acid cycle

2 acetyl groups 4 CO2

6 NADH + H+

2 FADH22 FAD


Citric Acid Cycle

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2 ADP 22

ATP

e–

NADH

e–

e–

Glycolysis

glucose pyruvatePreparatory reaction

2 ATP

2 ADP

4 ADP 4 ATP total

ATP net

Matrix

Citric acidcycle

NADH

NADHand FADH2


chemiosmosis

32 ADPor 34

32or 34

ATP

e–

e–

e–

e–

Figure 7.6

35


1. The C2 acetyl group combineswith a C4 molecule to produce

citrate, a C6 molecule.

C4

CoA

Citric acidcycle

Preparatoryreaction

CoA

acetyl CoA

Figure 7.6

36


1. The C2 acetyl group combineswith a C4 molecule to producecitrate, a C6 molecule.

NAD+

CO2

NADH + H+

2. Oxidationreactionsproduce twoNADH + H+.

citrate

C4

CoA

C5

Citric acidcycle

Preparatoryreaction

CoA

acetyl CoA

Figure 7.6

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ATP

1. The C2 acetyl group combines

with a C4 molecule to producecitrate, a C6 molecule.

NAD+

NADH + H+

CO2

NADH + H+

CO2

2. Oxidation

reactionsproduce twoNADH + H+.

citrate

The loss of two

CO2 results In a new C4

molecule.

C4

One ATP is produced

by substrate-level

ATP synthesis.

CoA

4.

C4

NAD+C5

3.

Citric acid

cycle

Preparatory

reaction

CoA

acetyl CoA

Figure 7.6

38


ATP


with a C4 molecule to producecitrate, a C6 molecule.

NADH + H+

NAD+

NADH + H+

CO2

NADH + H+

CO2

2. Oxidation

reactionsproduce twoNADH + H+.

citrate

The loss of two

CO2 results In a new C4

molecule.

C4

C4

One ATP is produced

by substrate-level

ATP synthesis.

NAD+

CoA

Additional oxidation reactions

produce an FADH2 and anotherNADH + H+ and regenerateoriginal C4 molecule.

4.

FAD

C4

FADH2

NAD+C5

5.

3.

Citric acid

cycle

Preparatory

reaction

CoA

acetyl CoA

Figure 7.6

39


ATP

2 ADT 22

ATP

e–

NADH

e–

e–

Glycolysis


2 ATP

2 ADP

4 ADP 4 ATP total

ATP net


with a C4 molecule to produce

citrate, a C6 molecule.

NADH + H+

Matrix

Citric acid

cycle

NADH

NADHand FADH2


chemiosmosis

32 ADPor 34

32or 34

ATP

NAD+

NADH + H+

CO2

NADH + H+

CO2

2. Oxidation

reactions

produce two

NADH + H+.

citrate

The loss of two

CO2 results

In a new C4

molecule.

C4

C4

One ATP is producedby substrate-levelATP synthesis.

NAD+

CoA

Additional oxidation reactions

produce an FADH2 and another

NADH + H+ and regenerate

original C4 molecule.

4.

FAD

C4

FADH2

NAD+C5

e–

e–

e–

e–

5.

3.

Citric acid

cycle

Preparatory

reaction

CoA

acetyl CoA

Figure 7.6

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Electron Transport Chain

• Electron Transport Chain

– Located in cristae of mitochondria

• Electrons are passed to a series of electron carriers.

– Some carriers are cytochromes, iron-containing proteins.

• High-energy electrons enter system and low-energy

electrons leave the system.

• Two electrons per NADH + H+ and FADH2 enter the

electron transport chain.

• Each carrier reduced and then oxidized.

41

Electron Transport Chain

– As electrons pass from one carrier to another, energy is captured and stored as a hydrogen ion concentration gradient.

– Oxygen combines with hydrogen ions to form water.

– NAD+ and FAD are recycled to pick up more electrons from glycolysis, prep reaction, and citric acid cycle.

42


2 ADT 22 ATP

NADH

e–

Glycolysis


2 ATP

2 ADP

4 ADP 4 ATP total

ATP net

Citric acid

cycle

NADH

NADH and

FADH2

Electron transport

chain andchemiosmosis

32 or ADP

34

32 or

34

ATP

e–

e–

e–

e–

e–

e–

Figure 7.7

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43


H2O

2H+

ADP + P

O212

ADP + P

ADP + P

ATP

ATP

ATP

FADH2

FAD + 2H+2e–

2e–

e–

e–

electron

carrier

2e–

2e–

2e–

made by

chemiosmosis

made by

chemiosmosis

made by

chemiosmosis

NAD+ + 2H+

NADH + H+

electron

carrier

electron

carrier

electron

carrier

electron

carrier

Figure 7.7

44


H2O

2H+

ADP + P

O2

12

ADP + P

ADP + P

ATP

ATP

ATP

FADH2

FAD + 2H+2e–

2e–

e–

e–

electron

carrier

2e–

2e–

2e–

made by

chemiosmosis

made by

chemiosmosis

made by

chemiosmosis

NAD+ + 2H+

NADH + H+

electron

carrier

electron

carrier

electron

carrier

electron

carrier

2 ADT 22 ATP

NADH

e–

Glycolysis

glucose pyruv atePreparatory reaction

2 ATP

2 ADP

4 ADP 4 ATP total

ATP net

Citric acid

cycle

NADH

NADH and

FADH2

Electron transport

chain and

chemiosmosis

32 or ADP

34

32 or

34

ATP

e–

e–

e–

e–

e–

e–

Figure 7.7

45

Organization of Cristae

• Electron carriers are located in the cristae of the

mitochondria.

• NADH pass electrons to first acceptor of the

electron transport chain.

• As electrons pass along a series of electron

carriers, the energy released is used to pump H+

into the intermembrane space of mitochondrion.

• Protons accumulate in the intermembranous

space (proton gradient).

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Organization of Cristae

• The cristae also have ATP synthase

complexes.

• The H+ ions flow through an ATP synthase

complex, back into the matrix.

• As the H+ pass through the complex, energy is

released and captured to form ATP from ADP.

– This process is called chemiosmosis.

47


cristae

intermembrane space matrix

Figure 7.8

48


2

ADP + H2O

NAD+

H+

H+H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

P

2+

O212

Electron transportchain

proteincomplex

e-

FADH2

matrix

ATP synthase

complex

H+H+ATP

channelprotein

intermembrane

spacechemiosmosis

FAD

NADH + H+

ATP

e-

ATP

e-

e-e-

Figure 7.8

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49


cristae

2

ADP + H2O

NAD+

H+

H+H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

H+

P

2+

O212

intermembrane space matrix

Electron transportchain

protein

complex

e-

FADH2

matrix

ATP synthasecomplex

H+H+ATP

channelprotein

intermembranespace

chemiosmosis

FAD

NADH + H+

ATP

e-

ATP

e-

e-e-

Figure 7.8

50

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Energy Yield from Cellular Respiration

• What is the energy yield for the complete

breakdown of glucose to CO2 and H2O?

– Total of 4 ATP by substrate-level ATP synthesis

• 2 net from glycolysis

• 2 from citric acid cycle

– 32-34 ATP produced by electron transport chain and chemiosmosis

• Some cells have to pay to pump NADH from glycolysis into mitochondria

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Cyto

pla

sm

Mit

och

on

dri

on

Ele

ctr

on

tra

nsp

ort

ch

ain

2net

2

glucose

subtotal subtotal

2 CO2

4 CO2

FADH2

2

2

6

2

4 or 6

6

18

4

324

6 O2

ATP

or 34

ATP

ATP

ATP

ATPATP

ATP

ATP

ATP

2 pyruvate

2 acetyl CoA

Citric acidcycle

NADH + H+

NADH + H+

NADH + H+

glycolysis

6 H2O

36 or 38totalFigure 7.9

53

Efficiency of Cellular Respiration

• The difference in energy content of reactants (glucose and oxygen) and products (carbon dioxide and water) is 686 kcal.

• ATP phosphate bond has 7.3 kcal of energy.

• 36 ATP are produced in respiration.

• 36 X 7.3 = 263 kcal.

• 263/686 = 39% efficiency of energy capture.

• The rest of the energy is lost as heat.

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7.1 Overview of Cellular · PDF file8/30/2013 3 7 Phases of Cellular Respiration • Glycolysis is the breakdown of glucose into two molecules of pyruvate. – Oxidation by removal