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CAMPBELL

BIOLOGY Reece • Urry • Cain • Wasserman • Minorsky • Jackson

© 2014 Pearson Education, Inc.

TENTH

EDITION

CAMPBELL

BIOLOGY Reece • Urry • Cain • Wasserman • Minorsky • Jackson

TENTH

EDITION

Cellular

Respiration and

Fermentation

Lecture Presentation by

Nicole Tunbridge and

Kathleen Fitzpatrick

9


Life Is Work

Living cells require energy from outside sources

Some animals, such as the giraffe, 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 generate ATP, which powers work


Figure 9.2

Light energy

Organic molecules

O2 CO2 H2O +

Photosynthesis in chloroplasts

Cellular respiration in mitochondria

ECOSYSTEM

ATP powers most cellular work ATP

Heat energy

+


BioFlix: The Carbon Cycle


Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels

Catabolic pathways release stored energy by

breaking down complex molecules

Electron transfer plays a major role in these

pathways

These processes are central to cellular respiration


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

Methane (reducing

agent)

Oxygen (oxidizing

agent)

Carbon dioxide Water

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

NAD+

2 e− + 2 H+

2[H] (from food)

Nicotinamide (oxidized form)

Reduction of NAD+

2 e− + H+

NADH

Nicotinamide (reduced form)

Oxidation of NADH H+

H+

Dehydrogenase


Figure 9.4a

NAD+

Nicotinamide (oxidized form)


Figure 9.4b

2 e− + 2 H+

Reduction of NAD+

2 e− + H+

NADH

Nicotinamide (reduced form)

Oxidation of NADH H+

H+

Dehydrogenase

2[H] (from food)


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

H2 + ½ O2

2 H + ½ O2

2 H+

2 e−

2 e− 2 H+ +

H2O

½ O2

Controlled release of

energy

ATP

ATP

ATP

Explosive release

Cellular respiration Uncontrolled reaction (a) (b)

Fre

e e

nerg

y,

G

Fre

e e

nerg

y,

G

H2O


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

1.

2.

3.

GLYCOLYSIS (color-coded blue throughout the chapter)

PYRUVATE OXIDATION and the CITRIC ACID CYCLE

(color-coded orange)

OXIDATIVE PHOSPHORYLATION: Electron transport and

chemiosmosis (color-coded purple)


Figure 9.6-1

Electrons via NADH

ATP

CYTOSOL MITOCHONDRION

Substrate-level

GLYCOLYSIS

Glucose Pyruvate


Figure 9.6-2

Electrons via NADH

Electrons via NADH

and FADH2

ATP ATP


Substrate-level Substrate-level

GLYCOLYSIS PYRUVATE OXIDATION CITRIC

ACID CYCLE Acetyl CoA Glucose Pyruvate


Figure 9.6-3

Electrons via NADH

Electrons via NADH

and FADH2

ATP ATP ATP


Substrate-level Substrate-level Oxidative

GLYCOLYSIS PYRUVATE OXIDATION CITRIC

ACID CYCLE

OXIDATIVE PHOSPHORYLATION

(Electron transport and chemiosmosis)

Acetyl CoA Glucose Pyruvate


BioFlix: Cellular Respiration


The process that generates most of the ATP is

called oxidative phosphorylation because it is

powered by redox reactions


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

Enzyme Enzyme

Substrate

Product

ATP

ADP

P


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

Glycolysis (“sugar splitting”) 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.UN06

GLYCOLYSIS PYRUVATE

OXIDATION

CITRIC

ACID

CYCLE

OXIDATIVE

PHOSPHORYL-

ATION

ATP


Figure 9.8

Energy Investment Phase

Glucose

Energy Payoff Phase

Net

2 ATP used 2 ADP + 2 P

4 ADP + 4 P 4 ATP formed

NAD+ 4 e− 2 + + 4 H+ 2 H+ 2 NADH

Pyruvate 2

2

2

2

2

2

2

2 H+ H+

4

4

Glucose Pyruvate

ATP ATP used ATP formed

H2O

NADH

−

2 NAD+

+

+

+

+ + +

2 H2O

4 e−


Figure 9.9a

GLYCOLYSIS: Energy Investment Phase

ADP

Glucose 6-phosphate

Fructose 6-phosphate

ATP ATP

ADP

Glyceraldehyde 3-phosphate (G3P)

Fructose 1,6-bisphosphate

Dihydroxyacetone phosphate (DHAP)

Glucose

Hexokinase Phosphogluco- isomerase

Phospho- fructokinase

Aldolase

Isomerase

1 2

5

4 3


Figure 9.9aa-1


Glucose


Figure 9.9aa-2


Glucose 6-phosphate

ATP

ADP Glucose

Hexokinase

1


Figure 9.9aa-3


Glucose 6-phosphate

ATP

ADP Glucose

Hexokinase Phosphogluco- isomerase


1 2


Figure 9.9ab-1




Figure 9.9ab-2


3


ATP

ADP




Figure 9.9ab-3


3 4

5


ATP

ADP

Glyceraldehyde 3-phosphate (G3P)


Dihydroxyacetone phosphate (DHAP)


Aldolase

Isomerase


Figure 9.9b

GLYCOLYSIS: Energy Payoff Phase

Glycer-

aldehyde

3-phosphate

(G3P)

Triose

phosphate

dehydrogenase

6 1,3-Bisphospho-

glycerate

3-Phospho-

glycerate

2-Phospho-

glycerate

Phosphoenol-

pyruvate (PEP)

Pyruvate

Phospho-

glycerokinase

Phospho-

glyceromutase

Enolase Pyruvate

kinase

2 NAD+

7 8 9

10

2 NADH

+ 2 H+

2

2

2

2

2 2 2 2

2

2 2 H2O

ATP ATP ADP

ADP


Figure 9.9ba-1


4

Glyceraldehyde

3-phosphate (G3P)

Dihydroxyacetone

phosphate (DHAP)

Aldolase

Isomerase

5


Figure 9.9ba-2


4

Glyceraldehyde

3-phosphate (G3P)

Dihydroxyacetone

phosphate (DHAP)

Aldolase

Isomerase

5 6

Triose

phosphate

dehydrogenase

2 NAD+ 2 H+

NADH

2

2

2

2

1,3-Bisphospho-

glycerate


Figure 9.9ba-3


4

Glyceraldehyde

3-phosphate (G3P)

Dihydroxyacetone

phosphate (DHAP)

Aldolase

Isomerase

5 6 7

Triose

phosphate

dehydrogenase

2 NAD+ 2 H+

NADH

2

2

2

2

2 ADP

1,3-Bisphospho-

glycerate

3-Phospho-

glycerate

Phospho-

glycerokinase

2

2

ATP


Figure 9.9bb-1

3-Phospho-

glycerate

2



Figure 9.9bb-2

8 9

Phospho-

glyceromutase

3-Phospho-

glycerate

2-Phospho-

glycerate

2 2 2

Enolase

Phosphoenol-

pyruvate (PEP)

2 H2O



Figure 9.9bb-3

8 9

10

Phospho-

glyceromutase

3-Phospho-

glycerate

2-Phospho-

glycerate

2 2 2

Enolase

Phosphoenol-

pyruvate (PEP)

Pyruvate

Pyruvate

kinase

2

2 ATP ADP

2 H2O 2



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.UN07

GLYCOLYSIS PYRUVATE

OXIDATION

CITRIC

ACID

CYCLE

OXIDATIVE

PHOSPHORYL-

ATION


Figure 9.10

CYTOSOL

Pyruvate

Transport protein

MITOCHONDRION

Acetyl CoA NAD+ H+ NADH +

CO2

Coenzyme A

1

2

3


The Citric Acid Cycle

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


Figure 9.11

PYRUVATE OXIDATION

Pyruvate (from glycolysis,

2 molecules per glucose)

NADH

NAD+

CO2

CoA

CoA

+ H+

CoA

CoA

CO2

CITRIC

ACID

CYCLE

FADH2

FAD

ATP

ADP + P i

NAD+

+ 3 H+

NADH 3

3

2

Acetyl CoA


Figure 9.11a

PYRUVATE OXIDATION

Pyruvate (from glycolysis,

2 molecules per glucose)

NADH

NAD+

CO2

CoA

CoA

+ H+ Acetyl CoA


Figure 9.11b

CoA

CoA

CO2

CITRIC

ACID

CYCLE

FADH2

FAD

ATP

ADP + P i

NAD+

+ 3 H+

NADH 3

3

2

Acetyl CoA


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.UN08

GLYCOLYSIS PYRUVATE

OXIDATION

CITRIC

ACID

CYCLE

OXIDATIVE

PHOSPHORYL-

ATION

ATP


Figure 9.12-1

Acetyl CoA

Oxaloacetate

CoA-SH

Citrate

CITRIC

ACID

CYCLE

1


Figure 9.12-2

Acetyl CoA

H2O

Oxaloacetate

CoA-SH

Citrate

CITRIC

ACID

CYCLE

Isocitrate

1

2


Figure 9.12-3

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

NAD+

CO2

NADH CITRIC

ACID

CYCLE

Isocitrate

1

2

3


Figure 9.12-4

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

CoA-SH

NAD+

CO2

NADH

CO2 NAD+

NADH

+ H+

Succinyl

CoA

CITRIC

ACID

CYCLE

Isocitrate

1

2

4

3


Figure 9.12-5

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

CoA-SH

NAD+

CO2

NADH

CO2 NAD+

NADH

+ H+

Succinyl

CoA

ATP

ADP

GTP GDP

Succinate

CITRIC

ACID

CYCLE

P i

Isocitrate

1

2

5

4

3

CoA-SH


Figure 9.12-6

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

CoA-SH

NAD+

CO2

NADH

CO2 NAD+

NADH

+ H+

Succinyl

CoA

ATP

ADP

GTP GDP

Succinate

FAD

FADH2

Fumarate

CITRIC

ACID

CYCLE

P i

Isocitrate

1

2

5

6 4

3

CoA-SH


Figure 9.12-7

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

CoA-SH

NAD+

CO2

NADH

CO2 NAD+

NADH

+ H+

Succinyl

CoA

ATP

ADP

GTP GDP

Succinate

FAD

FADH2

Fumarate

H2O

Malate

CITRIC

ACID

CYCLE

P i

Isocitrate

1

2

5

6 4

3 7

CoA-SH


Figure 9.12-8

Acetyl CoA

H2O

+ H+

Oxaloacetate

CoA-SH

Citrate

-Ketoglutarate

CoA-SH

NAD+

CO2

NADH

CO2 NAD+

NADH

+ H+

Succinyl

CoA

ATP

ADP

GTP GDP

Succinate

FAD

FADH2

Fumarate

H2O

Malate

CITRIC

ACID

CYCLE

+ H+

NAD+

P i

NADH

Isocitrate

1

2

5

6 4

3 7

8

CoA-SH


Figure 9.12a

Acetyl CoA

Oxaloacetate

Citrate Isocitrate

H2O

CoA-SH

1

2


Figure 9.12b

3

4 -Ketoglutarate

CO2

NAD+

NADH

+ H+

CO2

NAD+

NADH

+ H+

CoA-SH

Isocitrate

Succinyl

CoA


Figure 9.12c

Succinyl

CoA

6

5

Fumarate

FADH2

FAD

Succinate

GTP GDP

ADP

ATP

P i

CoA-SH


Figure 9.12d

NADH

Oxaloacetate

Malate

Fumarate

H2O

7

8

NAD+

+ H+


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.UN09

GLYCOLYSIS CITRIC

ACID

CYCLE

PYRUVATE

OXIDATION

ATP

OXIDATIVE

PHOSPHORYL-

ATION


Figure 9.13

NADH

e− 2 NAD+

FADH2

FAD 2 e

−

FMN

Fe•S

Q

Fe•S

Cyt b

Fe•S

Cyt c1

Cyt c

Cyt a

Cyt a3

e− 2

(originally from

NADH or FADH2)

2 H+ + ½ O2

H2O

Multiprotein

complexes I

II

III

IV

50

40

30

20

10

0

Fre

e e

nerg

y (

G)

rela

tive

to

O2 (

kc

al/

mo

l)


Figure 9.13a

50

40

30

20

10

Fre

e e

ne

rgy (

G)

rela

tiv

e t

o O

2 (

kc

al/m

ol)

NADH

e− 2

NAD+

FADH2

Fe•S

e−

FMN

Fe•S

Q

Cyt b

FAD I

II

FAD

Multiprotein

complexes

III

Fe•S

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

2

e− 2


Figure 9.13b

30

20

10

Fre

e e

ne

rgy (

G)

rela

tiv

e t

o O

2 (

kc

al/m

ol)

0

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

e− 2

2 H+ + ½ O2

H2O

(originally from

NADH or FADH2)


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 protein complex, 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 9.14

INTERMEMBRANE

SPACE Rotor

H+ Stator

Internal rod

Catalytic

knob

ADP + P i

MITOCHONDRIAL

MATRIX

ATP


Video: ATP Synthase 3-D Structure, Top View


Video: ATP Synthase 3-D Structure, Side View


Figure 9.15

Protein

complex

of electron

carriers

(carrying

electrons

from

food)

ATP

synthase

Electron transport chain Chemiosmosis

Oxidative phosphorylation

2 H+ + ½ O2 H2O

ADP + P i

H+

ATP

H+

H+

H+

H+

Cyt c

Q

I

II

III

IV

FAD FADH2

NADH NAD+

1 2


Figure 9.15a

Protein complex of electron carriers

2 H+ + ½ O2 H2O

H+

NAD+

1

H+

H+

NADH

FADH2

Cyt c Cyt c

IV

III

II

I

FAD

(carrying electrons from food) Electron transport chain

Q


Figure 9.15b

H+

2

H+

ADP + P i ATP

Chemiosmosis

ATP

synthase


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 shuttles

span membrane

CYTOSOL 2 NADH

or

2 FADH2

2 NADH 2 FADH2 6 NADH

MITOCHONDRION

OXIDATIVE

PHOSPHORYLATION

(Electron transport

and chemiosmosis)

CITRIC

ACID

CYCLE

PYRUVATE

OXIDATION

2 Acetyl CoA

GLYCOLYSIS

Glucose 2 Pyruvate

+ 2 ATP + 2 ATP

Maximum per glucose: About

30 or 32 ATP

+ about 26 or 28 ATP

2 NADH


Figure 9.16a

Electron shuttles

span membrane

+ 2 ATP

2 NADH or

2 FADH2

GLYCOLYSIS

Glucose 2 Pyruvate

2 NADH


Figure 9.16b

2 FADH2 6 NADH

CITRIC

ACID

CYCLE

PYRUVATE

OXIDATION

2 Acetyl CoA

+ 2 ATP

2 NADH


Figure 9.16c

2 NADH or

2 FADH2

2 NADH 2 FADH2 6 NADH

OXIDATIVE

PHOSPHORYLATION

(Electron transport

and chemiosmosis)

+ about 26 or 28 ATP


Figure 9.16d

Maximum per glucose: About

30 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 anaerobic

respiration or fermentation 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

The first step releases CO2

The second step produces ethanol

Alcohol fermentation by yeast is used in brewing,

winemaking, and baking


Figure 9.17

2 ADP + 2 P i 2 ATP

Glucose

2 NAD+ NADH 2

+ 2 H+

2 Pyruvate

CO2 2

2 Ethanol

(a) Alcohol fermentation

2 Acetaldehyde 2 Lactate

Lactic acid fermentation

2 ADP + 2 P i 2 ATP

GLYCOLYSIS

NAD+

+ 2 H+

NADH 2 2

2 Pyruvate

(b)

GLYCOLYSIS Glucose


Figure 9.17a

2 ADP + 2 P i

NAD+

+ 2 H+

GLYCOLYSIS Glucose

2 ATP

2 2

2 Ethanol 2 Acetaldehyde

2 Pyruvate

(a) Alcohol fermentation

2 CO2 NADH


Figure 9.17b

2 ADP + 2 P i

NAD+

+ 2 H+

GLYCOLYSIS Glucose

2 ATP

2 2

Lactate

(b) Lactic acid fermentation

NADH

2 Pyruvate

2


Animation: Fermentation Overview


In lactic acid fermentation, pyruvate is reduced

by 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


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 mechanisms for

oxidizing NADH:

In fermentation, an organic molecule (such as

pyruvate or acetaldehyde) acts as a final electron

acceptor

In cellular respiration electrons are transferred to

the electron transport chain

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 9.18

Glucose

Glycolysis CYTOSOL

Pyruvate

No O2 present:

Fermentation

O2 present:

Aerobic cellular

respiration

Ethanol,

lactate, or

other products

MITOCHONDRION

Acetyl CoA

CITRIC

ACID

CYCLE


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 9.19-1

Proteins Carbohydrates Fats

Amino

acids Sugars Glycerol Fatty

acids


Figure 9.19-2


Amino


acids

GLYCOLYSIS

Glucose

Glyceraldehyde 3- P

Pyruvate NH3


Figure 9.19-3


Amino


acids

GLYCOLYSIS

Glucose

Glyceraldehyde 3- P

Pyruvate

Acetyl CoA

NH3


Figure 9.19-4


Amino


acids

GLYCOLYSIS

Glucose

Glyceraldehyde 3- P

Pyruvate

Acetyl CoA

CITRIC

ACID

CYCLE

NH3


Figure 9.19-5


Amino


acids

GLYCOLYSIS

Glucose

Glyceraldehyde 3- P

Pyruvate

Acetyl CoA

CITRIC

ACID

CYCLE

OXIDATIVE

PHOSPHORYLATION

NH3


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 metabolic 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

Glucose

AMP

Stimulates

GLYCOLYSIS


Phosphofructokinase

Fructose 1,6-bisphosphate Inhibits Inhibits

Citrate

Pyruvate

Acetyl CoA ATP

CITRIC

ACID

CYCLE

Oxidative

phosphorylation


Figure 9.UN10a


Figure 9.UN10b


Figure 9.UN11

Inputs Outputs

Glucose 2 Pyruvate 2 2 + + NADH ATP

GLYCOLYSIS


Figure 9.UN12

Inputs Outputs

CITRIC

ACID

CYCLE

2 Pyruvate 2 Acetyl CoA

2 Oxaloacetate

2

2 6

8

FADH2

NADH ATP

CO2


Figure 9.UN13

INTERMEMBRANE

SPACE

Protein complex

of electron

carriers

H+

H+ H+

2 H+ + ½ O2 H2O

MITOCHONDRIAL MATRIX

(carrying electrons from food)

NADH NAD+

FADH2

I

II

III

IV

Cyt c

Q

FAD


Figure 9.UN14

INTER-

MEMBRANE

SPACE H+

MITOCHON-

DRIAL

MATRIX ATP

synthase

ADP + P i H+ ATP


Figure 9.UN15

Low ATP

concentration

High ATP

concentration


concentration

Ph

osp

ho

fru

cto

kin

ase

acti

vit

y


Figure 9.UN16

pH

dif

fere

nce

acro

ss m

em

bra

ne

Time


Figure 9.UN17

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