Cellular Respiration

PowerPoint® Lecture Presentations for

Biology
Eighth Edition
Neil Campbell and Jane Reece

Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
 Overview: Life Is Work

• Living cells require energy from outside

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

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 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

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Fig. 9-2

Light
energy

ECOSYSTEM

Photosynthesis
in chloroplasts
CO2 + H2O Organic + O
molecules 2
Cellular respiration
in mitochondria

ATP

ATP powers most cellular work

Heat
energy
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

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• 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)

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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)
LEO says GER or OIL RIG
becomes oxidized
(loses electron)

becomes reduced
(gains electron)
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
 Reactants Products
becomes oxidized

becomes reduced

Methane Oxygen Carbon dioxide Water

(reducing (oxidizing
agent) agent)
Oxidation of Organic Fuel Molecules During Cellular
Respiration
During cellular respiration, the fuel (such as
glucose) is oxidized, and O2 is reduced.

becomes oxidized

becomes reduced

Dehydrogenase
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
Electrons from organic compounds are usually
first transferred to NAD+ (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
 2 e– + 2 H+
2 e– + H+
NADH H+
Dehydrogenase
Reduction of NAD+
NAD+ + 2[H] + H+
Oxidation of NADH
Nicotinamide
(reduced form)

Nicotinamide
(oxidized form)
NADH passes the electrons to the electron
transport chain…ETC
Unlike an uncontrolled reaction, the electron
transport chain passes electrons in a series of
steps instead of one explosive reaction
O2 (high electro negativity) pulls electrons down
the chain in an energy-yielding tumble
The energy yielded is used to regenerate ATP
from ADP and inorganic Phosphate
The Stages of Cellular Respiration: A Preview

• Cellular respiration 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)

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Fig. 9-6-1

Electrons
carried
via NADH

Glycolysis

Glucose Pyruvate

Cytosol

ATP

Substrate-level
phosphorylation
Fig. 9-6-2

Electrons Electrons carried

carried via NADH and
via NADH FADH2

Glycolysis Citric
acid
Glucose Pyruvate cycle

Mitochondrion
Cytosol

ATP ATP

Substrate-level Substrate-level
phosphorylation phosphorylation
Fig. 9-6-3

Electrons Electrons carried

carried via NADH and
via NADH FADH2

Oxidative
Glycolysis Citric phosphorylation:
acid electron transport
Glucose Pyruvate cycle and
chemiosmosis

Mitochondrion
Cytosol

ATP ATP ATP

Substrate-level Substrate-level Oxidative

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

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• 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

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Fig. 9-7

Enzyme Enzyme

ADP
P
Substrate + ATP
Product
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

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Fig. 9-8

Energy investment phase

Glucose

2 ADP + 2 P 2 ATP used

Energy payoff phase

4 ADP + 4 P 4 ATP formed

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2 Pyruvate + 2 H2O

Net
Glucose 2 Pyruvate + 2 H2O
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
Fig. 9-9-1

Glucose

ATP
1
Hexokinase

ADP

Glucose
Glucose-6-phosphate

ATP
1
Hexokinase

ADP

Glucose-6-phosphate
Fig. 9-9-2

Glucose

ATP
1
Hexokinase

ADP

Glucose-6-phosphate
Glucose-6-phosphate

2
Phosphoglucoisomerase

2
Fructose-6-phosphate
Phosphogluco-
isomerase

Fructose-6-phosphate
Fig. 9-9-3

Glucose

ATP
1
Hexokinase

ADP

Fructose-6-phosphate
Glucose-6-phosphate

2
Phosphoglucoisomerase

ATP
3
Fructose-6-phosphate
Phosphofructo-
ATP
kinase
3
Phosphofructokinase
ADP
ADP

Fructose-
1, 6-bisphosphate

Fructose-
1, 6-bisphosphate
Fig. 9-9-4

Glucose

ATP
1
Hexokinase

ADP

Glucose-6-phosphate

2
Phosphoglucoisomerase
Fructose-
1, 6-bisphosphate

4
Fructose-6-phosphate
Aldolase
ATP
3
Phosphofructokinase

ADP

5
Isomerase
Fructose-
1, 6-bisphosphate

4
Aldolase

5
Isomerase
Dihydroxyacetone Glyceraldehyde-
phosphate 3-phosphate
Dihydroxyacetone Glyceraldehyde-
phosphate 3-phosphate
Fig. 9-9-5
2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate

Glyceraldehyde-
3-phosphate

2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate
Fig. 9-9-6
2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate
2 ADP

7
Phosphoglycerokinase
2 ATP

2 1, 3-Bisphosphoglycerate
2 ADP
2 3-Phosphoglycerate
7
Phosphoglycero-
2 ATP kinase

2 3-Phosphoglycerate
Fig. 9-9-7
2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate
2 ADP

7 Phosphoglycerokinase

2 ATP

3-Phosphoglycerate
2 3-Phosphoglycerate

8
2
Phosphoglyceromutase

8
Phosphoglycero-
2 2-Phosphoglycerate mutase

2 2-Phosphoglycerate
Fig. 9-9-8
2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate
2 ADP

7 Phosphoglycerokinase

2 ATP

2 3-Phosphoglycerate 2 2-Phosphoglycerate
8
Phosphoglyceromutase

9
Enolase
2 H2O
2 2-Phosphoglycerate

9
Enolase
2 H2O

2 Phosphoenolpyruvate

2 Phosphoenolpyruvate
Fig. 9-9-9
2 NAD+ 6
Triose phosphate
dehydrogenase
2 NADH 2 Pi
+ 2 H+

2 1, 3-Bisphosphoglycerate
2 ADP
7 Phosphoglycerokinase

2 ATP

2 Phosphoenolpyruvate
2 ADP
2 3-Phosphoglycerate

8
Phosphoglyceromutase 10
Pyruvate
2 ATP kinase
2 2-Phosphoglycerate

9
Enolase
2 H2O

2 Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP

2 Pyruvate

2 Pyruvate
CITRIC ACID CYCLE
KREBS CYCLE /
TRICARBOXYLIC ACID/ TCA
CYCLE

Essentially involves the oxidation of acetyl CoA

to CO2 and H2O.
This Cycle utilizes about two-third of total
oxygen consumed by the body.

35
Coenzyme A

The key cofactor in first step of the TCA cycle

 Location of
Brief History: Overview
TCA
• Hans Adolf • Mitochondrial • 65-70% of the
Krebs matrix ATP is
synthesized
• 1937 • In close
proximity to • Name : TCA
• Studies of the electronic used because
oxygen transport at the ouset of
consumption chain. the cycle
in pigeon tricarboxylic
breast muscle. acids
participate.

37
 SALIENT FEATURES OF CITRIC ACID
CYCLE/KREB’S CYCLE
▪ The final common oxidative pathway for carbohydrate, fats
and amino acids.
▪ The cycle operates only under aerobic conditions.
▪ The enzymes of TCA cycle are located in mitochondrial
matrix.
▪ It involves the combination of a two carbon acetyl CoA with
a four carbon oxaloacetate to produce a six carbon
tricarboxvlic acid, citrate
▪ Oxaloacetate is considered to play a catalytic role in. citric
acid cycle
Acetyl CoA + 3 NAD+ + FAD + GDP + Pi +2H2O 2CO2 + 3NADH +
3H+ + FADH2 + GTP + CoA
Citric Acid Cycle/Kreb’s
Cycle Process
Concept 9.3: The citric acid cycle completes the
energy-yielding oxidation of organic molecules
• In the presence of O2, pyruvate enters the
mitochondrion
• Before the citric acid cycle can begin, pyruvate
must be converted to acetyl CoA, which links
the cycle to glycolysis

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Fig. 9-10

CYTOSOL MITOCHONDRION

NAD+ NADH + H+

1 3
Acetyl CoA
Pyruvate CO2 Coenzyme A

Transport protein
• The citric acid cycle, also called the Krebs
cycle, takes place within the mitochondrial
matrix
• The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn

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Fig. 9-11

Pyruvate

CO2
NAD+
CoA
NADH
+ H+ Acetyl CoA
CoA

CoA

Citric
acid
cycle 2 CO2

FADH2 3 NAD+

FAD 3 NADH
+ 3 H+
ADP + P i

ATP
• 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
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Fig. 9-12-1

Acetyl CoA
CoA—SH

Oxaloacetate

Citrate

Citric
acid
cycle
Fig. 9-12-2

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Citrate
Isocitrate

Citric
acid
cycle
Fig. 9-12-3

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Citrate
Isocitrate
NAD+
Citric NADH
3
acid + H+
cycle
CO2

-Keto-
glutarate
Fig. 9-12-4

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Citrate
Isocitrate
NAD+
Citric NADH
acid 3
+ H+
cycle
CO2

CoA—SH
-Keto-
glutarate
4

CO2
NAD+

NADH
Succinyl + H+
CoA
Fig. 9-12-5

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Citrate
Isocitrate
NAD+
Citric NADH
3
acid + H+
cycle
CO2

CoA—SH
-Keto-
glutarate
4
CoA—SH

5
CO2
NAD+

Succinate Pi NADH
GTP GDP Succinyl + H+
CoA
ADP

ATP
Fig. 9-12-6

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Citrate
Isocitrate
NAD+
Citric NADH
3
acid + H+
cycle
CO2

Fumarate CoA—SH
-Keto-
glutarate
6 4
CoA—SH

FADH2 5
CO 2
NAD+
FAD
Succinate Pi NADH
GTP GDP Succinyl + H+
CoA
ADP

ATP
Fig. 9-12-7

Acetyl CoA
CoA—SH

1 H2O

Oxaloacetate
2

Malate Citrate
Isocitrate
NAD+
Citric 3
NADH
7
acid + H+
H2O cycle
CO2

Fumarate CoA—SH
-Keto-
glutarate
6 4
CoA—SH

FADH2 5
CO 2
NAD+
FAD
Succinate Pi NADH
GTP GDP Succinyl + H+
CoA
ADP

ATP
Fig. 9-12-8

Acetyl CoA
CoA—SH

NADH
+H+ 1 H2O

NAD+
8 Oxaloacetate
2

Malate Citrate
Isocitrate
NAD+
Citric 3
NADH
acid + H+
7
H2O cycle
CO2

Fumarate CoA—SH
-Keto-
glutarate
6 4
CoA—SH

FADH2 5
CO 2
NAD+
FAD
Succinate Pi NADH
GTP GDP Succinyl + H+
CoA
ADP

ATP
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

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The Pathway of Electron Transport

• The electron transport chain is in the 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
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Fig. 9-13

NADH

50
2 e– NAD+
FADH2

2 e– FAD
Multiprotein
40  FAD complexes
FMN
Fe•S Fe•S 
Q

Cyt b
Fe•S
30
Cyt c1 I
Cyt c V
Cyt a
Cyt a3
20

10 2 e–
(from NADH
or FADH2)

0 2 H+ + 1/2 O2

H2O
• Electrons are transferred from NADH or FADH2
to the electron transport chain
• Electrons are passed through a number of
proteins to O2
• The electron transport chain generates no ATP
• The chain’s function is to break the large free-
energy drop from food to O2 into smaller steps
that release energy in manageable amounts

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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 channels in 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

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Fig. 9-14
INTERMEMBRANE SPACE

H+
Stator
Rotor

Internal
rod

Cata-
lytic
knob

ADP
+
P ATP
i

MITOCHONDRIAL MATRIX
• 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

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Fig. 9-16

H+
H+

H+
H+
Protein complex Cyt c
of electron
carriers

V
Q
 
ATP
synthase

2 H+ + 1/2O2 H2O
FADH2
FAD

NADH NAD+
ADP + P i ATP
(carrying electrons
from food)
H+

1 Electron transport chain 2 Chemiosmosis

Oxidative phosphorylation
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 40% of the energy in a glucose molecule

is transferred to ATP during cellular respiration,
making about 38 ATP

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Fig. 9-17

CYTOSOL Electron shuttles MITOCHONDRION

span membrane 2 NADH
or
2 FADH2

2 NADH 2 NADH 6 NADH 2 FADH2

Glycolysis Oxidative
2 2 Citric phosphorylation:
Glucose Pyruvate Acetyl acid electron transport
CoA cycle and
chemiosmosis

+ 2 ATP + 2 ATP + about 32 or 34 ATP

Maximum per glucose: About

36 or 38 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
• Glycolysis can produce ATP with or without O2
(in aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with
fermentation or anaerobic respiration to
produce ATP

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• Anaerobic respiration uses an electron
transport chain with an electron acceptor other
than O2, for example sulfate
• Fermentation uses phosphorylation instead of
an electron transport chain to generate ATP

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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

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• 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

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Fig. 9-18

2 ADP + 2 Pi 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NAD+ 2 NADH 2 CO2

+ 2 H+

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation

2 ADP + 2 Pi 2 ATP

Glucose Glycolysis

2 NAD+ 2 NADH
+ 2 H+
2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fig. 9-18a

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NAD+ 2 NADH 2 CO 2
+ 2 H+

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation

• 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

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Fig. 9-18b

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 NAD+ 2 NADH
+ 2 H+
2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

Fermentation and Aerobic Respiration Compared

• Both processes use glycolysis to oxidize

glucose and other organic fuels to pyruvate
• 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 38 ATP per

glucose molecule; fermentation produces 2
ATP per glucose molecule

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• 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

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Fig. 9-19
Glucose

Glycolysis
CYTOSOL

Pyruvate

No O2 present: O2 present:
Fermentation Aerobic cellular
respiration

MITOCHONDRION
Ethanol Acetyl CoA
or
lactate
Citric
acid
cycle
The Evolutionary Significance of Glycolysis

• Glycolysis occurs in nearly all organisms

• Glycolysis probably evolved in ancient
prokaryotes before there was oxygen in the
atmosphere

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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

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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

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• 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

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Fig. 9-20
Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty

acids acids

Glycolysis
Glucose

Glyceraldehyde-3- P

NH3 Pyruvate

Acetyl CoA

Citric
acid
cycle

Oxidative
phosphorylation
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 on

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

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Fig. 9-21
Glucose

AMP
Glycolysis
Fructose-6-phosphate Stimulates
+
Phosphofructokinase
–
–
Fructose-1,6-bisphosphate
Inhibits Inhibits

Pyruvate

ATP Citrate
Acetyl CoA

Citric
acid
cycle

Oxidative
phosphorylation
Fig. 9-UN5

Inputs Outputs

2 ATP
Glycolysis
+

2 NADH

Glucose 2 Pyruvate
Fig. 9-UN6

Inputs Outputs

S—CoA
2 ATP
C O
CH3

2 Acetyl CoA
6 NADH

O C COO
Citric acid
CH2 cycle

COO 2 FADH2
2 Oxaloacetate