Biology in Focus - Chapter 7

CAMPBELL BIOLOGY IN FOCUS
© 2014 Pearson Education, Inc.
Urry • Cain • Wasserman • Minorsky • Jackson • Reece
Lecture Presentations by
Kathleen Fitzpatrick and Nicole Tunbridge
7
Cellular
Respiration
and Fermentation

Overview: 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 7.1

 Energy flows into an ecosystem as sunlight and
leaves as heat
 Photosynthesis generates O2 and organic molecules,
which are used as fuel for cellular respiration
 Cells use chemical energy stored in organic
molecules to regenerate ATP, which powers work
Animation: Carbon Cycle

Figure 7.2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2 + H2O
Cellular respiration
in mitochondria
Organic
molecules
+ O2
ATP
ATP powers
most cellular work
Heat
energy

Concept 7.1: 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 7.UN01
becomes oxidized
(loses electron)
becomes reduced
(gains electron)

Figure 7.UN02
becomes oxidized
becomes reduced

 The electron donor is called the reducing agent
 The electron acceptor 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 7.3
Reactants Products
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide Water
becomes reduced
becomes oxidized

 Redox reactions that move electrons closer to
electronegative atoms, like oxygen, release chemical
energy that can be put to work

Oxidation of Organic Fuel Molecules During
Cellular Respiration
 During cellular respiration, the fuel (such as glucose)
is oxidized, and O2 is reduced
 Organic molecules with an abundance of hydrogen,
like carbohydrates and fats, are excellent fuels
 As hydrogen (with its electron) is transferred to
oxygen, energy is released that can be used in ATP
sythesis

Figure 7.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 7.4
NAD+
Nicotinamide
(oxidized form)
Nicotinamide
(reduced form)
Oxidation of NADH
Reduction of NAD+
Dehydrogenase
NADH
+ 2[H]
(from food)
2 e−
+ 2 H+
2 e−
+ H+
H+
H+
+

Figure 7.4a
NAD+
Nicotinamide
(oxidized form)

Figure 7.4b
Nicotinamide
(reduced form)
Oxidation of NADH
Reduction of NAD+
Dehydrogenase
NADH
2 e−
+ 2 H+
2 e−
+ H+
H+
H++ 2[H]
(from food)
+

Figure 7.UN04

 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 7.5
Explosive
release
(a) Uncontrolled reaction (b) Cellular respiration
H2O
Freeenergy,G
Freeenergy,G
Electrontransport
chain
Controlled
release of
energy
H2O
2 H+
2 e−
2 H+
+ 2 e−
ATP
ATP
ATP
½
½
½H2 + O2 O2
O2
2 H +

The Stages of Cellular Respiration: A Preview
 Harvesting of energy from glucose has three stages
 Glycolysis (breaks down glucose into two molecules
of pyruvate)
 Pyruvate oxidation and the citric acid cycle
(completes the breakdown of glucose)
 Oxidative phosphorylation (accounts for most of
the ATP synthesis)
Animation: Cellular Respiration

Figure 7.UN05
Glycolysis (color-coded teal throughout the chapter)
Pyruvate oxidation and the citric acid cycle
(color-coded salmon)
1.
Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)
2.
3.

Figure 7.6-1
Electrons
via NADH
Glycolysis
Glucose Pyruvate
CYTOSOL
ATP
Substrate-level
MITOCHONDRION

Figure 7.6-2
Electrons
via NADH
Glycolysis
Glucose Pyruvate
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Electrons
via NADH and
FADH2
CYTOSOL
ATP
Substrate-level
ATP
Substrate-level
MITOCHONDRION

Figure 7.6-3
Electrons
via NADH
Glycolysis
Glucose Pyruvate
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Electrons
via NADH and
FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
CYTOSOL
ATP
Substrate-level
ATP
Substrate-level
MITOCHONDRION
ATP
Oxidative

 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 7.7
Substrate
P
ADP
Product
ATP+
Enzyme Enzyme

Concept 7.2: 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 7.UN06
Glycolysis Pyruvate
oxidation
Citric
acid
cycle
Oxidative
phosphorylation
ATP ATP ATP

Figure 7.8
Energy Investment Phase
Energy Payoff Phase
Net
Glucose
Glucose
2 ADP + 2 P
4 ADP + 4 P
2 NAD+
+ 4 e−
+ 4 H+
2 NAD+
+ 4 e−
+ 4 H+
4 ATP formed − 2 ATP used
2 ATP
4 ATP
used
formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2O
2 NADH + 2 H+
2 ATP

Figure 7.9a
Glycolysis: Energy Investment Phase
Glucose
ATP
ADP
Glucose
6-phosphate
Phosphogluco-
isomerase
Hexokinase
1
2 3
4
ATP
ADP
Fructose
6-phosphate
Phospho-
fructokinase
Fructose
1,6-bisphosphate
Aldolase
Isomerase
5
Glyceraldehyde
3-phosphate (G3P)
Dihydroxyacetone
phosphate (DHAP)

Figure 7.9aa-1
Glucose

Figure 7.9aa-2
Glucose
Glucose
6-phosphate
ADP
ATP
Hexokinase
1

Figure 7.9aa-3
Glucose
Glucose
6-phosphate
ADP
ATP
Hexokinase
1
Fructose
6-phosphate
Phosphogluco-
isomerase
2

Figure 7.9ab-1
Fructose
6-phosphate

Figure 7.9ab-2
Fructose
6-phosphate
Phospho-
fructokinase
3
Fructose
1,6-bisphosphate
ATP
ADP

Figure 7.9ab-3
Fructose
6-phosphate
Phospho-
fructokinase
3
Aldolase
Isomerase
4
5
Fructose
1,6-bisphosphate
Glyceraldehyde
3-phosphate (G3P)
ATP
ADP
Dihydroxyacetone
phosphate (DHAP)

Figure 7.9b
Glycolysis: Energy Payoff Phase
2 NAD+
Glyceraldehyde
3-phosphate (G3P)
Triose
phosphate
dehydrogenase
6
+ 2 H+
2 NADH
2
2 P
i
1,3-Bisphospho-
glycerate
3-Phospho-
glycerate
2-Phospho-
glycerate
Phosphoenol-
pyruvate (PEP)
Pyruvate
Phospho-
glycerokinase
Phospho-
glyceromutase
Enolase Pyruvate
kinase
2 ADP 2 2 2 2
2 ADP
2 ATP
2 H2O
2 ATP
9
1087

Figure 7.9ba-1
Isomerase
4
Glyceraldehyde
3-phosphate (G3P)
Dihydroxyacetone
phosphate (DHAP)
Aldolase
5

Figure 7.9ba-2
Isomerase
Glyceraldehyde
3-phosphate (G3P)
Dihydroxyacetone
phosphate (DHAP)
2 NAD+
Triose
phosphate
dehydrogenase
+ 2 H+
2 NADH
2
1,3-Bisphospho-
glycerate
2
Aldolase
P
i
5 6
4

Figure 7.9ba-3
Isomerase
Glyceraldehyde
3-phosphate (G3P)
Dihydroxyacetone
phosphate (DHAP)
2 NAD+
Triose
phosphate
dehydrogenase
+ 2 H+
2 NADH
2
1,3-Bisphospho-
glycerate
3-Phospho-
glycerate
Phospho-
glycerokinase
2 ADP
2 ATP
2
Aldolase
P
i
2
5 7
6
4

Figure 7.9bb-1
3-Phospho-
glycerate
2

Figure 7.9bb-2
83-Phospho-
glycerate
Phospho-
glyceromutase
222
2 H2O
2-Phospho-
glycerate
Phosphoenol-
pyruvate (PEP)
Enolase
9

Figure 7.9bb-3
3-Phospho-
glycerate
2 ATP
Phospho-
glyceromutase
2222
2 ADP
2 H2O
2-Phospho-
glycerate
Phosphoenol-
pyruvate (PEP)
Pyruvate
Enolase Pyruvate
kinase
9
108

Concept 7.3: 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
 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

Figure 7.UN07
Glycolysis Pyruvate
oxidation
Citric
acid
cycle
Oxidative
phosphorylation
ATP ATP ATP

Figure 7.10
CYTOSOLPyruvate
(from glycolysis,
2 molecules per glucose)
CO2
CoA
NAD+
NADH
MITOCHONDRION CoA
CoA
Acetyl CoA+ H+
Citric
acid
cycle
FADH2
FAD
ADP + P
i
ATP
NADH
3 NAD+
3
+ 3 H+
2 CO2

Figure 7.10a
CYTOSOLPyruvate
(from glycolysis,
2 molecules per glucose)
CO2
CoA
NAD+
NADH
MITOCHONDRION CoA
Acetyl CoA+ H+

Figure 7.10b
CoA
Citric
acid
cycle
FADH2
FAD
ADP + P
i
ATP
NADH
3 NAD+
3
+ 3 H+
2 CO2
CoA
Acetyl CoA

 The citric acid cycle, also called the Krebs cycle,
completes the breakdown of pyruvate to CO2
 The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2
per turn

Figure 7.UN08
Glycolysis Pyruvate
oxidation
Oxidative
phosphorylation
ATP ATP ATP
Citric
acid
cycle

Figure 7.11-1
Acetyl CoA
Oxaloacetate
CoA-SH
Citrate
H2O
Isocitrate
Citric
acid
cycle
2
1

Figure 7.11-2
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD+
+ H+
CO2
α-Ketoglutarate
Citric
acid
cycle
3
1
CoA-SH
2

Figure 7.11-3
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD+
+ H+
CO2
α-Ketoglutarate
Citric
acid
cycle
CoA-SH
CO2
NAD+
NADH
+ H+
Succinyl
CoA
4
1
3
CoA-SH
2

Figure 7.11-4
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD+
+ H+
CO2
α-Ketoglutarate
Citric
acid
cycle
CoA-SH
CO2
NAD+
NADH
+ H+
ATP formation
Succinyl
CoA
ADP
GDPGTP
P
i
ATP
Succinate
5
4
1
CoA-SH
3
CoA-SH
2

Figure 7.11-5
Malate
Succinate
FAD
FADH2
Fumarate
H2O
7
6
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD+
+ H+
CO2
α-Ketoglutarate
Citric
acid
cycle
CoA-SH
CO2
NAD+
NADH
+ H+
ATP formation
Succinyl
CoA
ADP
GDPGTP
P
i
ATP
5
4
1
CoA-SH
3
CoA-SH
2

Figure 7.11-6
NADH
NAD+
+ H+
8
Malate
Succinate
FAD
FADH2
Fumarate
H2O
7
6
Acetyl CoA
Oxaloacetate
Citrate
H2O
Isocitrate
NADH
NAD+
+ H+
CO2
α-Ketoglutarate
Citric
acid
cycle
CoA-SH
CO2
NAD+
NADH
+ H+
ATP formation
Succinyl
CoA
ADP
GDPGTP
P
i
ATP
5
4
1
CoA-SH
3
CoA-SH
2

Figure 7.11a
CoA-SH
Acetyl CoA
Start: Acetyl CoA adds its
two-carbon group to
oxaloacetate, producing
citrate; this is a highly
exergonic reaction.
Oxaloacetate
Citrate
Isocitrate
H2O1
2

Figure 7.11b
Isocitrate Redox reaction:
Isocitrate is oxidized;
NAD+
is reduced.
Redox reaction:
After CO2 release, the resulting
four-carbon molecule is oxidized
(reducing NAD+
), then made
reactive by addition of CoA.
CO2 release
CO2 release
α-Ketoglutarate
Succinyl
CoA
NAD+
NADH
+ H+
CO2
CO2
CoA-SH
NAD+
NADH
+ H+
3
4

Figure 7.11c
CoA-SH
Redox reaction:
Succinate is oxidized;
FAD is reduced.
Fumarate
Succinate
Succinyl
CoA
ATP formation
ATP
ADP
GDPGTP
FAD
FADH2
P
i
5
6

Figure 7.11d
Redox reaction:
Malate is oxidized;
NAD+
is reduced.
Fumarate
Malate
Oxaloacetate
H2O
NAD+
+ H+
NADH
7
8

 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

Concept 7.4: 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 7.UN09
Glycolysis
Pyruvate
oxidation
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP ATP ATP

Figure 7.12
Multiprotein
complexes
(originally from
NADH or FADH2)
Freeenergy(G)relativetoO2(kcal/mol)
50
40
30
20
10
0
NADH
NAD+
FADH2
FAD
2
2
e−
e−
FMN
Fe•S Fe•S
Q
I
II
III
Cyt b
Cyt c1
Fe•S
Cyt c
IV
Cyt a
Cyt a3
2 e−
O22 H+
+ ½
H2O

Figure 7.12a
Multiprotein
complexes
50
40
30
20
10
NADH
NAD+
FADH2
FAD
2
2
e−
e−
FMN
Fe•S Fe•S
Q
I
II
III
Cyt b
Cyt c1
Fe•S
Cyt c
IV
Cyt a
Cyt a3
2 e−

Figure 7.12b
30
20
10
0
Cyt c1
Cyt c
IV
Cyt a
Cyt a3
2 e−
(originally from
NADH or FADH2)
2 H+
+ ½ O2
H2O

 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

Video: ATP Synthase 3-D Side View
Video: ATP Synthase 3-D Top View

Figure 7.13
INTERMEMBRANE SPACE
MITOCHONDRIAL MATRIX
Rotor
Internal rod
Catalytic knob
Stator
H+
ATP
ADP
P
i
+

 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

Figure 7.14
Protein
complex
of electron
carriers
H+
H+
H+
H+
Q
I
II
III
FADH2
FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
Oxidative phosphorylation
Chemiosmosis
ATP
synthase
H+
ADP + ATPP
i
H2O2 H+
+ ½ O2
IV
Cyt c
1 2

Figure 7.14a
Protein
complex
of electron
carriers
H+
Q
I
II
III
FADH2
FAD
NAD+
NADH
(carrying electrons
from food)
Electron transport chain
H2O2 H+
+ ½ O2
Cyt c
1
IV
H+
H+

Figure 7.14b
ATP
synthase
Chemiosmosis2
H+
H+
ADP + P
i
ATP

An Accounting of ATP Production by Cellular
Respiration
 During cellular respiration, most energy flows in the
following 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
molecules is not known exactly

Figure 7.15
Electron shuttles
span membrane
CYTOSOL
2 NADH
2 NADH
2 FADH2
or
2 NADH
Glycolysis
Glucose 2
Pyruvate
Pyruvate
oxidation
2 Acetyl CoA
Citric
acid
cycle
6 NADH 2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 26 or 28 ATP+ 2 ATP + 2 ATP
About
30 or 32 ATP
Maximum per glucose:
MITOCHONDRION

Figure 7.15a
Electron shuttles
span membrane
2 NADH
2 FADH2
or
2 NADH
Glycolysis
Glucose 2
Pyruvate
+ 2 ATP

Figure 7.15b
2 NADH 6 NADH 2 FADH2
Citric
acid
cycle
Pyruvate
oxidation
2 Acetyl CoA
+ 2 ATP

Figure 7.15c
2 NADH
2 NADH 6 NADH 2 FADH2
2 FADH2
or
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 26 or 28 ATP

Figure 7.15d
Maximum per glucose:
About
30 or 32 ATP

Concept 7.5: 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
 The first step releases CO2 from pyruvate, and the
second step reduces acetaldehyde to ethanol
 Alcohol fermentation by yeast is used in brewing,
winemaking, and baking
Animation: Fermentation Overview

Figure 7.16
2 ADP + 2 2 ATPP
i
Glucose Glycolysis
2 Pyruvate
2 CO2
2 NADH
+ 2 H+
2 NAD+
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde
(b) Lactic acid fermentation
2 Lactate
2 NADH
+ 2 H+
2 NAD+
2 Pyruvate
Glycolysis
2 ATP2 ADP + 2 P
i
Glucose

Figure 7.16a
2 ADP + 2 2 ATPP
i
Glucose Glycolysis
2 Pyruvate
2 CO2
2 NADH
+ 2 H+
2 NAD+
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde

Figure 7.16b
2 ADP + 2 2 ATPP
i
Glucose Glycolysis
2 Pyruvate
2 NADH
+ 2 H+
2 NAD+
(b) Lactic acid fermentation
2 Lactate

 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 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 only 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 7.17
Glucose
CYTOSOL
Glycolysis
Pyruvate
O2 present:
Aerobic cellular
respiration
No O2 present:
Fermentation
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
MITOCHONDRION

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 7.6: 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 and amino
groups must be removed before amino acids can
feed glycolysis or the citric acid cycle

 Fats are digested to glycerol (used in glycolysis) and
fatty acids
 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 7.18-1
Proteins
Amino
acids
Carbohydrates
Sugars
Fats
Glycerol Fatty
acids

Figure 7.18-2
Proteins
Amino
acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
NH3
Fats
Glycerol Fatty
acids

Figure 7.18-3
Proteins
Amino
acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
NH3
Fats
Glycerol Fatty
acids

Figure 7.18-4
Proteins
Amino
acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
Citric
acid
cycle
NH3
Fats
Glycerol Fatty
acids

Figure 7.18-5
Proteins
Amino
acids
Carbohydrates
Sugars
Glucose
Glycolysis
Glyceraldehyde 3-
Pyruvate
P
Acetyl CoA
Citric
acid
cycle
NH3
Fats
Glycerol Fatty
acids
Oxidative
phosphorylation

Biosynthesis (Anabolic Pathways)
 The body uses small molecules to build other
substances
 Some of these small molecules come directly from
food; others can be produced during glycolysis or
the citric acid cycle

Figure 7.UN10a

Figure 7.UN10b

Figure 7.UN11
Inputs
Glucose
Glycolysis
2 Pyruvate + 2
Outputs
ATP NADH+ 2

Figure 7.UN12
Inputs
2 Pyruvate 2 Acetyl CoA
2 Oxaloacetate
Citric
acid
cycle
Outputs
ATP
CO2
2
6 2
8 NADH
FADH2

Figure 7.UN13a
Protein
complex
of electron
carriers
INTERMEMBRANE
SPACE
MITOCHONDRIAL MATRIX
(carrying electrons from food)
NADH NAD+
FADH2
FAD
Cyt c
Q
I
II
III
IV
2 H+
+
½O2
H2O
H+
H+
H+

Figure 7.UN13b
INTER-
MEMBRANE
SPACE
MITO-
CHONDRIAL
MATRIX
ATP
synthase
ATPADP + H+
H+
P
i

Figure 7.UN14
Time
pHdifference
acrossmembrane

Biology in Focus - Chapter 7

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