09 Lecture Presentation

LECTURE PRESENTATIONSFor CAMPBELL BIOLOGY, NINTH EDITION

Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson

© 2011 Pearson Education, Inc.

Lectures byErin Barley

Kathleen Fitzpatrick

Cellular Respiration and Fermentation

Chapter 9

Overview: Life Is Work

• Living cells require energy from outside sources

• Some animals, such as the chimpanzee, obtain energy by eating plants, and some animals feed on other organisms that eat plants


Figure 9.1

• Energy flows into an ecosystem as sunlight and leaves as heat

• Photosynthesis generates O2 and organic molecules, which are used in cellular respiration

• Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work


Figure 9.2

Lightenergy

ECOSYSTEM

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

CO2 H2O O2Organic

molecules

ATP powersmost cellular workATP

Heatenergy

Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

• Several processes are central to cellular respiration and related pathways


Catabolic Pathways and Production of ATP

• The breakdown of organic molecules is exergonic

• Fermentation is a partial degradation of sugars that occurs without O2

• Aerobic respiration consumes organic molecules and O2 and yields ATP

• Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2


• Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration

• Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular 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 chemical reactions releases energy stored in organic molecules

• This released energy is ultimately used to synthesize ATP


The Principle of Redox

• Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions

• In oxidation, a substance loses electrons, or is oxidized

• In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)


Figure 9.UN01

becomes oxidized(loses electron)

becomes reduced(gains electron)

Figure 9.UN02

becomes oxidized

becomes reduced

• The electron donor is called the reducing agent

• The electron receptor is called the oxidizing agent

• Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds

• An example is the reaction between methane and 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 as glucose) 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 organic molecules are broken down in a series of steps

• Electrons from organic compounds are usually first transferred to NAD+, a coenzyme

• As an electron acceptor, NAD+ functions as an oxidizing 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

Figure 9.UN04

Dehydrogenase

• NADH passes the electrons to the electron transport chain

• Unlike an uncontrolled reaction, the electron transport 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

Free

ene

rgy,

G

Free

ene

rgy,

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

Electron transport

chain

(from food via NADH)

The Stages of Cellular Respiration: A Preview

• Harvesting of energy from glucose has three stages

– Glycolysis (breaks down glucose into two molecules of pyruvate)

– The citric acid cycle (completes the breakdown 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 andchemiosmosis (color-coded violet)

3.

Figure 9.6-1

Electronscarried

via NADH

Glycolysis

Glucose Pyruvate

CYTOSOL MITOCHONDRION

ATP

Substrate-levelphosphorylation

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

Oxidativephosphorylation:electron transport

andchemiosmosis


ATP ATP ATP



Oxidative phosphorylation

• The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions


BioFlix: Cellular Respiration

• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration

• A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

• For each molecule of glucose degraded to CO2

and water by respiration, the cell makes up to 32 molecules of ATP


Figure 9.7

Substrate

Product

ADP

PATP

Enzyme Enzyme

Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

• Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate

• Glycolysis occurs in the cytoplasm and has two major phases

– Energy investment phase– Energy payoff phase

• Glycolysis occurs whether or not O2 is present


Figure 9.8

Energy Investment Phase

Glucose

2 ADP 2 P

4 ADP 4 P

Energy 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 NADH2 NAD + 2 H

2 P i

1,3-Bisphospho-glycerate6

Triosephosphate

dehydrogenase

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

9Triose

phosphatedehydrogenase

Figure 9.9-9


2 ATP 2 ATP2 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 6Isomerase

Figure 9.9c


2 NADH2 ATP

2 ADP 22

2 NAD + 2 H

2 P i

3-Phospho-glycerate


Triosephosphate

dehydrogenase


67

Figure 9.9d


2 ATP2 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 the mitochondrion (in eukaryotic cells) where the oxidation of glucose is completed


Oxidation of Pyruvate to Acetyl CoA

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

• This step is carried out by a multienzyme complex 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 pyruvate to CO2

• The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn


The Citric Acid Cycle

Figure 9.11Pyruvate

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, each catalyzed by a specific enzyme

• The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate

• The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle

• The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron 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

Citricacidcycle

NADH+ H

NAD

H2O

3

2

CoA-SH

CO2

Oxaloacetate

Figure 9.12-4

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Citricacidcycle

NADH

NADH

+ H

+ H

NAD

NAD

H2O

3

2

4

CoA-SH

CO2

CoA-SH

CO2

Oxaloacetate

Figure 9.12-5

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Citricacidcycle

NADH

NADH

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDPP i

3

2

4

5

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12-6

1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Fumarate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

ADP

GTP GDPP 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

SuccinylCoA

Succinate

Fumarate

Malate

Citricacidcycle

NADH

NADH

FADH2

ATP

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDPP i

FAD

3

2

4

5

6

7

CoA-SH

CO2

CoA-SH

CoA-SH

CO2

Oxaloacetate

Figure 9.12-8

NADH1

Acetyl CoA

CitrateIsocitrate

-Ketoglutarate

SuccinylCoA

Succinate

Fumarate

Malate

Citricacidcycle

NAD

NADH

NADH

FADH2

ATP

+ H

+ H

+ H

NAD

NAD

H2O

H2O

ADP

GTP GDPP 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

Figure 9.12c

Fumarate

FADH2

CoA-SH6

SuccinateSuccinyl

CoA

FAD

ADP

GTP GDPP 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 the energy extracted from food

• These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation


The Pathway of Electron Transport

• The electron transport chain is in the inner membrane (cristae) of the mitochondrion

• Most of the chain’s components are proteins, which exist in multiprotein complexes

• The carriers alternate reduced and oxidized states as they accept and donate electrons

• Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O


Figure 9.13NADH

FADH2

2 H + 1/2 O2

2 e

2 e

2 e

H2O

NAD

Multiproteincomplexes

(originally from NADH or FADH2)

III

III

IV

50

40

30

20

10

0

Free

ene

rgy

(G) r

elat

ive

to O

2 (kc

al/m

ol)

FMNFeS FeS

FAD

QCyt b

Cyt c1

Cyt cCyt 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 ATP directly

• It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts


Chemiosmosis: The Energy-Coupling Mechanism

• Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial 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+ to drive phosphorylation of ATP

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


Figure 9.14INTERMEMBRANE SPACE

RotorStator

H

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

IIIIV

Q

Cyt c

FADFADH2

NADH ADP P i

NAD

H

2 H + 1/2O2

H

HH

21

H

H2O

ATP

• The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis

• The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work


An Accounting of ATP Production by Cellular Respiration

• During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain proton-motive force ATP

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

• There are several reasons why the number of ATP is not known exactly


Figure 9.16

Electron shuttlesspan membrane

MITOCHONDRION2 NADH

2 NADH 2 NADH 6 NADH

2 FADH2

2 FADH2

or

2 ATP 2 ATP about 26 or 28 ATP

Glycolysis

Glucose 2 Pyruvate

Pyruvate oxidation

2 Acetyl CoACitricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

CYTOSOL

Maximum per glucose: About30 or 32 ATP

Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen

• Most cellular respiration requires O2 to produce ATP

• Without O2, the electron transport chain will cease to operate

• In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP


• Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example sulfate

• Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP


Types of Fermentation

• Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis

• Two common types are alcohol fermentation and lactic acid fermentation


• In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2

• Alcohol fermentation by yeast is used in brewing, winemaking, and baking


Animation: Fermentation Overview

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 ADP 2 Pi

NAD2 H

2 Pi

2 NAD

2 H

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 reduced to NADH, forming lactate as an end product, with no release of CO2

• Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt

• Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce


(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 glucose and harvest chemical energy of food

• In all three, NAD+ is the oxidizing agent that accepts electrons during glycolysis

• The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration

• Cellular respiration produces 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule


• Obligate anaerobes carry out fermentation or anaerobic respiration and cannot survive in the presence of O2

• Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration

• In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes


Figure 9.18Glucose

CYTOSOL Glycolysis

Pyruvate

No O2 present:Fermentation

O2 present: Aerobic cellular respiration

Ethanol,lactate, or

other products

Acetyl CoAMITOCHONDRION

Citricacidcycle

The Evolutionary Significance of Glycolysis

• Ancient prokaryotes are thought to have used glycolysis long before there was oxygen in the atmosphere

• Very little O2 was available in the atmosphere until about 2.7 billion years ago, so early prokaryotes likely used only glycolysis to generate 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 major intersections to various catabolic and anabolic pathways


The Versatility of Catabolism

• Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

• Glycolysis accepts a wide range of carbohydrates

• Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle


• Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)

• Fatty acids are broken down by beta oxidation and yield acetyl CoA

• An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate


Figure 9.19CarbohydratesProteins

Fattyacids

Aminoacids

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


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 on regulating the activity of enzymes at strategic points in the catabolic pathway


Figure 9.20

Phosphofructokinase

Glucose

GlycolysisAMP

Stimulates

Fructose 6-phosphate

Fructose 1,6-bisphosphate

Pyruvate

Inhibits Inhibits

ATP Citrate

Citricacidcycle

Oxidativephosphorylation

Acetyl CoA

Figure 9.UN06

Inputs Outputs

GlucoseGlycolysis

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

Figure 9.UN10

Time

pH d

iffer

ence

acro

ss m

embr

ane

Figure 9.UN11

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