Cellular Respiration and FermentationFigure 9.UN05 1. Glycolysis (color-coded teal throughout the chapter) Pyruvate oxidation and the citric acid cycle (color-coded salmon) 2. Oxidative
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Cellular Respiration and Fermentation
لجنة الطب البشري
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 9.2
Lightenergy
ECOSYSTEM
Photosynthesisin chloroplasts
Cellular respirationin mitochondria
CO2 H2O O2Organic
molecules
ATP powersmost cellular work
ATP
Heatenergy
Concept 9.1: Catabolic pathways yield
energy by oxidizing organic fuels
• Several processes are central to cellular
respiration and related pathways
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
• 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)
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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)
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 9.5
(a) Uncontrolled reaction (b) Cellular respiration
Explosiverelease of
heat and lightenergy
Controlledrelease ofenergy for
synthesis ofATP
Fre
e e
nerg
y, G
Fre
e e
nerg
y, 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
(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)
© 2011 Pearson Education, Inc.
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 and
chemiosmosis (color-coded violet)
3.
Figure 9.6-1
Electrons
carried
via NADH
Glycolysis
Glucose Pyruvate
CYTOSOL MITOCHONDRION
ATP
Substrate-level
phosphorylation
Figure 9.6-2
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Pyruvate
oxidation
Acetyl CoA
Glycolysis
Glucose Pyruvate
CYTOSOL MITOCHONDRION
ATP ATP
Substrate-level
phosphorylationSubstrate-level
phosphorylation
Figure 9.6-3
Electrons
carried
via NADH
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Pyruvate
oxidation
Acetyl CoA
Glycolysis
Glucose Pyruvate
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
CYTOSOL MITOCHONDRION
ATP ATP ATP
Substrate-level
phosphorylationSubstrate-level
phosphorylation
Oxidative
phosphorylation
• The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
© 2011 Pearson Education, Inc.
BioFlix: Cellular Respiration
09_06CellularRespiration.mpg
• 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
© 2011 Pearson Education, Inc.
Figure 9.7
Substrate
Product
ADP
P
ATP
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
© 2011 Pearson Education, Inc.
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
Glycolysis: Energy Investment Phase
ATPGlucose Glucose 6-phosphate Fructose 6-phosphate
ADP
Hexokinase Phosphogluco-
isomerase1
2
Figure 9.9-3
Glycolysis: Energy Investment Phase
ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate
ADP ADP
Hexokinase Phosphogluco-
isomerasePhospho-
fructokinase1
2 3
Figure 9.9-4
Glycolysis: Energy Investment Phase
ATP ATPGlucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate
Dihydroxyacetonephosphate
Glyceraldehyde3-phosphate
Tostep 6
ADP ADP
Hexokinase Phosphogluco-
isomerasePhospho-
fructokinase
Aldolase
Isomerase
12 3 4
5
Figure 9.9-5
Glycolysis: Energy Payoff Phase
2 NADH
2 NAD + 2 H
2 P i
1,3-Bisphospho-glycerate6
Triose
phosphate
dehydrogenase
Figure 9.9-6
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2
Phospho-
glycerokinase
67
Triose
phosphate
dehydrogenase
Figure 9.9-7
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
2 2
Phospho-
glycerokinase
Phospho-
glyceromutase
67 8
Triose
phosphate
dehydrogenase
Figure 9.9-8
Glycolysis: Energy Payoff Phase
2 ATP2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
Phosphoenol-pyruvate (PEP)
2 2 2
2 H2O
Phospho-
glycerokinase
Phospho-
glyceromutaseEnolase
67 8
9
Triose
phosphate
dehydrogenase
Figure 9.9-9
Glycolysis: Energy Payoff Phase
2 ATP 2 ATP
2 NADH
2 NAD + 2 H
2 P i
2 ADP
1,3-Bisphospho-glycerate
3-Phospho-glycerate
2-Phospho-glycerate
Phosphoenol-pyruvate (PEP)
Pyruvate
2 ADP2 2 2
2 H2O
Phospho-
glycerokinase
Phospho-
glyceromutaseEnolase Pyruvate
kinase
67 8
910
Triose
phosphate
dehydrogenase
Figure 9.9a
Glycolysis: Energy Investment Phase
ATPGlucose Glucose 6-phosphate
ADP
Hexokinase
1
Fructose 6-phosphate
Phosphogluco-
isomerase
2
Figure 9.9b
Glycolysis: Energy Investment Phase
ATPFructose 6-phosphate
ADP
3
Fructose 1,6-bisphosphate
Phospho-
fructokinase
4
5
Aldolase
Dihydroxyacetonephosphate
Glyceraldehyde3-phosphate
Tostep 6
Isomerase
Figure 9.9c
Glycolysis: Energy Payoff Phase
2 NADH2 ATP
2 ADP 2
2
2 NAD + 2 H
2 P i
3-Phospho-
glycerate1,3-Bisphospho-
glycerate
Triose
phosphate
dehydrogenase
Phospho-
glycerokinase
67
Figure 9.9d
Glycolysis: Energy Payoff Phase
2 ATP
2 ADP2222
2 H2O
PyruvatePhosphoenol-
pyruvate (PEP)2-Phospho-
glycerate
3-Phospho-
glycerate8
910
Phospho-
glyceromutaseEnolase Pyruvate
kinase
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
The Citric Acid Cycle
Figure 9.11
Pyruvate
NAD
NADH
+ H Acetyl CoA
CO2
CoA
CoA
CoA
2 CO2
ADP + P i
FADH2
FAD
ATP
3 NADH
3 NAD
Citric
acid
cycle
+ 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
© 2011 Pearson Education, Inc.
Figure 9.12-1
1
Acetyl CoA
Citrate
Citric
acid
cycle
CoA-SH
Oxaloacetate
Figure 9.12-2
1
Acetyl CoA
CitrateIsocitrate
Citric
acid
cycle
H2O
2
CoA-SH
Oxaloacetate
Figure 9.12-3
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
Citric
acid
cycle
NADH
+ H
NAD
H2O
3
2
CoA-SH
CO2
Oxaloacetate
Figure 9.12-4
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
Succinyl
CoA
Citric
acid
cycle
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
Succinyl
CoA
Succinate
Citric
acid
cycle
NADH
NADH
ATP
+ H
+ H
NAD
NAD
H2O
ADP
GTP GDP
P i
3
2
4
5
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
Figure 9.12-6
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
Succinyl
CoA
Succinate
Fumarate
Citric
acid
cycle
NADH
NADH
FADH2
ATP
+ H
+ H
NAD
NAD
H2O
ADP
GTP GDP
P 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
Succinyl
CoA
Succinate
Fumarate
Malate
Citric
acid
cycle
NADH
NADH
FADH2
ATP
+ H
+ H
NAD
NAD
H2O
H2O
ADP
GTP GDP
P i
FAD
3
2
4
5
6
7
CoA-SH
CO2
CoA-SH
CoA-SH
CO2
Oxaloacetate
Figure 9.12-8
NADH
1
Acetyl CoA
CitrateIsocitrate
-Ketoglutarate
Succinyl
CoA
Succinate
Fumarate
Malate
Citric
acid
cycle
NAD
NADH
NADH
FADH2
ATP
+ H
+ H
+ H
NAD
NAD
H2O
H2O
ADP
GTP GDP
P 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
Succinyl
CoA
NADH
NADH
NAD
NAD
+ H
CoA-SH
CO2
CO2
3
4
+ H
Figure 9.12c
Fumarate
FADH2
CoA-SH6
Succinate
Succinyl
CoA
FAD
ADP
GTP GDP
P 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
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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
© 2011 Pearson Education, Inc.
Figure 9.13
NADH
FADH2
2 H + 1/2 O2
2 e
2 e
2 e
H2O
NAD
Multiprotein
complexes
(originally from
NADH or FADH2)
III
III
IV
50
40
30
20
10
0
Fre
e e
ne
rgy (
G)
rela
tive
to
O2
(kc
al/
mo
l)
FMN
FeS FeS
FAD
Q
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
FeS
• Electrons are transferred from NADH or FADH2to 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 9.14
INTERMEMBRANE SPACE
Rotor
StatorH
Internal
rod
Catalytic
knob
ADP
+
P i ATP
MITOCHONDRIAL MATRIX
Figure 9.15
Proteincomplexof electroncarriers
(carrying electronsfrom food)
Electron transport chain
Oxidative phosphorylation
Chemiosmosis
ATPsynth-ase
I
II
III
IVQ
Cyt c
FADFADH2
NADH ADP P iNAD
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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 CoA
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
CYTOSOL
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
fermentation or anaerobic respiration to
produce ATP
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• 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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Animation: Fermentation Overview
09_18FermentationOverview_A.html
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
NAD
2 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
© 2011 Pearson Education, Inc.
(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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 9.18
Glucose
CYTOSOLGlycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
Ethanol,
lactate, or
other products
Acetyl CoA
MITOCHONDRION
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 9.19
CarbohydratesProteins
Fatty
acids
Amino
acids
Sugars
Fats
Glycerol
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
© 2011 Pearson Education, Inc.
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
© 2011 Pearson Education, Inc.
Figure 9.20
Phosphofructokinase
Glucose
GlycolysisAMP
Stimulates
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Inhibits Inhibits
ATP Citrate
Citric
acid
cycle
Oxidative
phosphorylation
Acetyl CoA
Figure 9.UN06
Inputs Outputs
Glucose
Glycolysis
2 Pyruvate 2 ATP 2 NADH
Figure 9.UN07
Inputs Outputs
2 Pyruvate 2 Acetyl CoA
2 OxaloacetateCitric
acid
cycle
2
26
8ATP NADH
FADH2CO2
Figure 9.UN08
Protein complex
of electron
carriers
(carrying electrons from food)
INTERMEMBRANE
SPACE
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-
MEMBRANE
SPACE
HADP + P i
MITO-
CHONDRIAL
MATRIX
ATP
synthase
H
ATP
Figure 9.UN10
Time
pH
dif
fere
nce
acro
ss m
em
bra
ne
Figure 9.UN11
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