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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 9
Cellular Respiration and
Fermentation
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Life Is Work
• living cells require energy from outside sources
• some animals obtain energy by eating plants
• some animals feed on other organisms that eat
plants
• energy flows into an ecosystem as
sunlight and leaves as heat
• photosynthesis generates O2 and
organic molecules - used in cellular
respiration
• cells use chemical energy stored in
organic molecules to regenerate
ATP - powers work
Light
energy
ECOSYSTEM
CO2  H2O
Photosynthesis
in chloroplasts
Organic  O
2
molecules
Cellular respiration
in mitochondria
ATP ATP powers
most cellular work
Heat
energy
Catabolic Pathways and Production of ATP
• catabolism - the breakdown of organic molecules is exergonic
– potential energy is stored in chemical bonds
– result of the arrangement of electrons in these bonds
– breaking of these bonds releases this potential energy
• catabolic processes – anaerobic, fermentation & aerobic
• Fermentation = partial degradation of sugars that occurs
without O2
• Aerobic respiration consumes organic molecules (fuel) and O2
to yield ATP
– most prevalent and efficient catabolic process
– carried out by eukaryotic cells and most prokaryotic
• Anaerobic respiration - similar to aerobic respiration but
consumes compounds other than O2
– prokaryotic cells
• Cellular respiration includes both aerobic and
anaerobic respiration
– glycolysis, Kreb’s cycle and electron transport chain
– is often used to refer to aerobic respiration
• uses carbohydrates, fats, and proteins
• most cellular respiration starts with the sugar glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP +
heat)
• breakdown of glucose is exergonic
– ΔG = -686 kcal/mol
• creates ATP – powers the work of endergonic
processes
Redox Reactions: Oxidation and Reduction
• How do catabolic pathways decompose glucose and
yield energy
• through the transfer of electrons = oxidationreduction reactions or Redox reactions
– relocation of electrons releases stored potential energy
• this released energy is ultimately used to synthesize
ATP
The Principle of Redox
• redox reactions = chemical reactions that transfer electrons
between reactants
• oxidation = a substance loses electrons, or is oxidized
• reduction = a substance gains electrons, or is reduced (the amount
of positive charge is reduced)
becomes oxidized
becomes reduced
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
• the electron donor is
called the reducing
agent
– e.g. Xe- = reduces Y
• the electron receptor
is called the oxidizing
agent
– e.g. Y = oxidizes Xe by
removing its electrons
Reactants
becomes oxidized
Products
Energy
becomes reduced
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
• the problem becomes when you have covalent bonds
• i.e. not all redox reactions involve the complete transfer of electrons from one
substance to another
– but change the degree of electron sharing in covalent bonds
• an example is the reaction between methane and O2
–
–
–
–
in methane – covalent electrons are shared equally between the C and the Hs of methane
and the two Os of O2 - they are equally electronegative
BUT - O is a very electronegative element – one of the most potent oxidizing agents
when CO2 is formed - electrons are shared less equally between C and O – the O “pulls”
on the electrons harder – so the carbon has lost electrons (becomes oxidized)
the electrons are also shared less equally in the water – O has gained electrons & become
reduced
Reactants
becomes oxidized
Products
Energy
becomes reduced
Methane
(reducing
agent)
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
• energy must be added to pull an electron away from an atom
• the more electronegative an atom is – the more energy will be required for it to
become oxidized
– like rolling a ball uphill
– methane is not very electronegative – little energy is required for it to become
oxidized
• an electron loses potential energy as it shifts from a less electronegative atom to a
more electronegative atom
– just as a ball loses potential energy when it rolls downhill
– it releases this loss of potential energy as chemical energy - used for work
• an electron loses potential energy as it shifts from a
less electronegative atom to a more electronegative
atom
• a redox reaction that moves electrons closer to
oxygen – releases chemical energy
– e.g. form CO2 from methane – electrons move
from the Carbon (when in methane) closer to the
Oxygen of CO2 = ENERGY
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
• the carbon atoms of glucose are not very electronegative
• lose their potential energy when they combine with O2 to form CO2 –
move away from C and closer to O (more electronegative)
• in general – molecules with carbons are good sources of potential energy
– electrons will shift toward more electronegative atoms like oxygen
Oxidation of Organic Fuel Molecules During
Cellular Respiration
becomes oxidized
becomes reduced
• in respiration – the oxidation of glucose (loss of electrons)
transfers electrons to a lower energy state (lower G)
– as electrons move from a less electronegative compound (sugar) to a
more electronegative compound (CO2)
– this liberates energy – used to make ATP
• only the activation energy barrier prevents the transfer of electrons to
the lower energy state
• body temperature is not high enough to reach this activation energy barrier
– done by enzymes
• main sources of ATP in cells – carbohydrates and fats
Stepwise Energy Harvest via NAD+ and the
Electron Transport Chain
• so oxidizing glucose produces more electronegative compounds
and releases energy
• if you release this energy all at once – not very efficient
• in cellular respiration - glucose and other organic molecules are
broken down to these electronegative compounds in a series of
steps
– at key steps – electrons are stripped from glucose and
eventually transferred to O2
– in typical oxidation reactions - electrons that are transferred
travel with a proton (H+)
NAD+
• BUT electrons are not transferred directly
– first transferred to NAD+ - functions as a coenzyme
• NAD = nicotinamine adenine dinucleotide
• 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
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Nicotinamide
(oxidized form)
Oxidation of NADH
Nicotinamide
(reduced form)
• How does NAD+ trap electrons?
• transfer is dependent upon a kind of
enzyme called a Dehydrogenase
• dehydrogenases remove a pair of
hydrogen atoms and a pair of electrons
• ACTUALLY – dehydrogenase removes a
hydride ion/H- (two electrons and a
proton) and a proton (H+)
Figure 9.UN04
NAD
NADH
Dehydrogenase
Reduction of NAD
(from food)
Oxidation of NADH
Nicotinamide
(oxidized form)
Nicotinamide
(reduced form)
• one electron gets transferred onto the N+ of
NAD  N
• the second electron gets attached to the C4
carbon directly across from the N
• this is REDUCTION and produces a reduced
form of NAD (NAD-)
• one proton attaches to the nicotinamide ring 
NADH
• the other is released into the surroundings
Dehydrogenase
• the electrons lose very little of their potential energy
when they are transferred to NAD+
• each NADH represents stored energy that can be tapped
to make ATP when the electrons “fall” down an energy
gradient to oxygen

2H
1/
2
O2
1/
2
O2
(from food via NADH)
Explosive
release of
heat and light
energy
Free energy, G
2 H+  2 e
Free energy, G
• cellular respiration uses an
Electron Transport Chain to
break this fall into several
energy releasing steps
• NADH shuttles the
electrons to the top of the
hill
• O2 captures these
electrons along with H+ to
form water
H2  1/2 O2
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e
2 H+
H2O
(a) Uncontrolled reaction
H2O
(b) Cellular respiration
• electron transfer from NADH to O2 = -53 kcal/mol
• use of several redox reactions to allow electrons to fall
from one carrier to another

2H
1/
2
O2
1/
2
O2
(from food via NADH)
Explosive
release of
heat and light
energy
Free energy, G
2 H+  2 e
Free energy, G
• each “downhill” carrier is
more electronegative than
its “uphill” carrier &
capable of oxidizing it
• electrons eventually fall
down the ETC to a far more
stable location in an oxygen
atom
H2  1/2 O2
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e
2 H+
H2O
(a) Uncontrolled reaction
H2O
(b) Cellular respiration
BioFlix: Cellular Respiration
© 2011 Pearson Education, Inc.
The Stages of Cellular Respiration
• Harvesting of energy from glucose has three stages:
– Glycolysis –anaerobic process that breaks down glucose into two molecules
of pyruvate
• cytosol
– the citric acid cycle (Kreb’s Cycle) - completes the breakdown of glucose
• starting material = acetyl CoA (derived from pyruvate)
• matrix of the mitochondria (cytosol in prokaryotes)
– Oxidative phosphorylation = ETC and chemiosmosis
• generates most of the ATP
• powered by redox reactions
• inner mitochondrial membrane
(plasma membrane in prokaryotes)
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
• 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
• ALSO = some of the steps of Glycolysis and Citric Acid Cycle
are redox reactions involving dehydrogenases removing
protons and electrons and creating NADH
• for each molecule of glucose degraded to CO2 and water by
respiration- the cell makes up to 32 molecules of ATP
Enzyme
Enzyme
ADP
P
Substrate
ATP
Product
Glycolysis harvests chemical energy by oxidizing glucose to
pyruvate
Energy Investment Phase
• Glycolysis (“splitting of
sugar”) breaks down
glucose into two molecules
of pyruvate
• Glycolysis has two major
phases
– Energy investment
phase
– Energy payoff phase
• Glycolysis occurs whether
or not O2 is present
Glucose
2 ADP  2 P
2 ATP used
Energy Payoff Phase
4 ADP  4 P
2 NAD+  4 e  4 H+
4 ATP formed
2 NADH  2 H+
2 Pyruvate  2 H2O
Net
Glucose
4 ATP formed  2 ATP used
2 NAD+  4 e  4 H+
2 Pyruvate  2 H2O
2 ATP
2 NADH  2 H+
Figure 9.9-1
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
ADP
Hexokinase
1
1. Hexokinase – transfers a phosphate group from ATP
to glucose  glucose-6-phosphate
- makes the glucose it more chemically reactive
Figure 9.9-2
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ADP
Hexokinase
1
Phosphoglucoisomerase
2
2. Phosphoglucoisomerase – enzyme that catalyzes
the rearrangement of G6P into fructose-6-phosphate
Figure 9.9-3
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
Fructose 1,6-bisphosphate
ADP
ADP
Hexokinase
1
Phosphoglucoisomerase
Phosphofructokinase
2
3
3. Phosphofructokinase – transfers a phosphate group from
ATP to the opposite end of F6P  fructose-1,6-bisphosphate
-phosphofructokinase is the rate-limiting enzyme for the
glycolytic portion of cellular respiration
Figure 9.9-3
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
Fructose 1,6-bisphosphate
ADP
ADP
Hexokinase
1
Phosphoglucoisomerase
Phosphofructokinase
2
3
-phosphofructokinase catalyzes an irreversible step in glycolysis
-same is true for hexokinase and pyruvate kinase
-its activity is regulated by the reversible binding of an allosteric
effector
-inhibited by high levels of ATP – acts to lower its affinity for
fructose-6-phosphate
-ATP binds to the enzyme at a regulatory site – changes the shape of
the enzyme’s catalytic site
-reduced binding to F6P results
-enzyme can also can be inhibited through a drop in pH
Figure 9.9-4
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
ADP
ADP
Hexokinase
1
Fructose 1,6-bisphosphate
Phosphoglucoisomerase
Phosphofructokinase
2
3
Aldolase
Dihydroxyacetone
phosphate
4
Glyceraldehyde
3-phosphate
Isomerase
5
4. Aldolase – cleaves the 6 carbon F-1,6-BP into two 3-Carbon
sugars  dihydroxyacetone phosphate and glyceraldehyde-3phosphate - are isomers of each other
-DHAP is a aldose, G3P is a ketose
-if this could reach equilibrium – 96% would be DHAP
-BUT G3P is used as soon as it is formed – never reaches Eq.
To
step 6
Figure 9.9-4
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
Fructose 6-phosphate
ATP
ADP
ADP
Hexokinase
1
Fructose 1,6-bisphosphate
Phosphoglucoisomerase
Phosphofructokinase
2
3
Aldolase
Dihydroxyacetone
phosphate
4
Glyceraldehyde
3-phosphate
Isomerase
5
To
step 6
5. Triose phosphate Isomerase – converts DAHP  G3P
immediately after G3P is used
-G3P forms the main glycolytic pathway so the isomerase funnels
DHAP into this pathway by converting it into G3P
-the following reactions actually run twice!!! (two molecules of
G3P are produced)
Figure 9.9-5
Glycolysis: Energy Payoff Phase
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2Pi
6. Triose phosphate Dehydrogenase
-also known as Glyceraldehyde-3-phosphate
dehydrogenase (GAPDH)
-first step: removes 2 electrons and 2 protons from
1,3-Bisphosphoglycerate
G3P and transfers them to NAD+ to make NADH
-so G3P is oxidized and NAD+ is reduced
-transfer of electrons to a more electronegative
compound (NAD+) releases energy
-second step: energy released by this redox reaction
is used for phosphorylation of G3P  1,3bisphosphoglycerate
Figure 9.9-6
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
7. Phosphoglycerokinase:
– 1,3-BPG is unstable and has a high energy potential
-allows for the transfer of the phosphate group from C1 to ADP 
ATP is made via Substrate level Phosphorylation
-1,3-BPG is oxidized  3-phosphoglycerate
(when the phosphate group is bound to 1,3-BPG - one electron is pulled closer to
the O of the sugar – O is more electronegative than P
– when the P group is released, it takes it’s electron & the sugar loses it – i.e.
oxidized)
Figure 9.9-7
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
2
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
8
2-Phosphoglycerate
8. Phosphoglyceromutase:
transfer of the remaining
phosphate group from C3 to
C2  2-phosphoglycerate
Figure 9.9-8
Glycolysis: Energy Payoff Phase
2 ATP
2 H2O
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
2
1,3-Bisphosphoglycerate
7
Enolase
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
2
9
3-Phosphoglycerate
8
2-Phosphoglycerate
Phosphoenolpyruvate (PEP)
9. Enolase: extracts a water molecule from the sugar
and forms a double bond between C2 and C3 
phosphoenolpyruvate (PEP)
Figure 9.9-9
Glycolysis: Energy Payoff Phase
2 ATP
2 ATP
2 H2O
2 NADH
2 NAD
Triose
phosphate
dehydrogenase
6
+ 2 H
2 ADP
2
2
1,3-Bisphosphoglycerate
7
Enolase
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
9
3-Phosphoglycerate
8
2 ADP
2
2-Phosphoglycerate
Pyruvate
kinase
Phosphoenolpyruvate (PEP)
10
Pyruvate
10. Pyrvuate kinase: PEP is unstable and has a high
energy potential
-allows the transfer of the remaining P group to ADP
for the second round of Substrate Level
Phosphorylation  ATP is made
-this final step of glycolysis produces Pyruvate
Glycolysis Energy Tally
• 2 NADH from glycolysis = 4 ATP from ETC
• 4 ATP made through substrate
phosphorylation
• 2 ATP consumed
After pyruvate is oxidized, the citric acid cycle completes
the energy-yielding oxidation of organic molecules
• glycolysis releases less than a quarter of the chemical
energy in glucose
• most energy is still contained in pyruvate
• oxidation of pyruvate releases the remaining energy
• in eukaryotes and in the presence of O2- pyruvate
enters the mitochondrion - the oxidation of glucose is
completed
• takes place in the cytosol in prokaryotes
Transition Phase: Oxidation of Pyruvate to
Acetyl CoA
• before the citric acid cycle can begin- pyruvate must be converted to acetyl
Coenzyme A (acetyl CoA)
– links glycolysis to the citric acid cycle
• this transition step is carried out by a multienzyme complex in the matrix that
catalyzes three reactions = pyruvate dehydrogenase complex
• requires a transport pump to bring pyruvate into the matrix of the mitochondria
– powered by the H+ gradient of the electron transport chain
1. removal of the carboxyl
group as a molecule of
CO2  2 carbon
compound
2. oxidation into acetate &
transfer of electrons to
NAD+
3. coenzyme A attached via
its sulfur atom  acetyl
coA
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A
3
1
2
Pyruvate
Transport protein
NAD NADH + H
Acetyl CoA
Transition Phase Energy Tally
• 2 NADH from pyruvate oxidation = 6 ATP
from ETC
•
•
•
•
•
1. ethanol
2. lactate
3. acetyl coA
4. PEP  glucose
5. amino acids
•
the production of
lactate or ethanol is a
reduction reaction and
regenerates NAD+
this sustains glycolysis
by replenshing NAD+
•
The Citric Acid Cycle
Pyruvate
• citric acid cycle- also called the
Krebs cycle
• completes the break down of
pyruvate to CO2
CO2
NAD
CoA
NADH
+ H
Acetyl CoA
CoA
CoA
– two more CO2 produced per
pyruvate
– 6 total (including 2 from transition)
• generates 1 GTP/ATP, 3 NADH,
and 1 FADH2 per turn
• turns once for every pyruvate
made
• 2 pyruvates are made for each
glucose
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
+ 3 H
ADP + P i
ATP
The Citric Acid Cycle
• The citric acid cycle has eight steps, each catalyzed by a
specific enzyme
• two carbons (red) enter in the reduced form as an acetyl
group
• two different carbons (blue) leave as the oxidized form of CO2
• 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
Acetyl CoA
CoA-SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
1. Addition of Acetyl coA to oxaloacetate to produce
citrate
-catalyzed by Citrate synthase or CoA Synthase
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
2. Isomerization of citrate to iso-citrate: dehydration
reaction, followed by a hydration step creates this
isomer of citrate
-intermediate step creates cis-Aconitate (unstable)
Figure 9.12-3
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
3
NADH
+ H
CO2
-Ketoglutarate
3. Oxidation of isocitrate alpha-ketoglutarate: : 1st of the 4 redox reactions in
the citric acid cycle
-creates an unstable intermediate that loses a CO2 (oxidation)
-coupled to the reduction of NAD+ to NADH
- catalyzed by isocitrate dehydrogenase
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
4. Oxidation of -ketoglutarate 
succinyl coA: 2nd of the 4 redox
reactions in the citric acid cycle
-loss of another CO2 in the
oxidation reaction
-reduction of NAD+ to NADH
-CoA is added through an unstable
bond – ΔG is -8kcal/mol
-catalyzed by -ketoglutarate
dehydrogenase
-3 enzyme complex
-reactions similar to the creation of
acetyl coA
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
Acetyl CoA
CoA-SH
5. Conversion to succinate:
the energy released by the
cleavage of the CoA powers
the phosphorylation of GDP
 GTP
-the GTP can be used to
generate another ATP
through phosphate transfer
-catalyzed by Succinyl CoA
synthase (similar enzyme as
that added CoA to
oxaloacetate)
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
CoA-SH
5
NAD
Succinate
GTP GDP
CO2
NADH
Pi
Succinyl
CoA
+ H
ADP
ATP
-in other cells – ATP is made at this step
-bacteria, plants & some animal cells
Acetyl CoA
CoA-SH
6  8: Oxidation of succinate
to oxaloacetate: regeneration
of oxaloacetate is done in three
steps
6. Oxidation to Fumarate –
reduction of a FAD  FADH2
-FAD is used because the free
energy change is not enough to
reduce NAD+
7. Hydration to Malate –
addition of water rearranges
fumarate into malate
8. Oxidation to oxaloacetate –
coupled to reduction of
another NAD+  NADH
NADH
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Acetyl CoA
CoA-SH
NADH
CITRIC ACID CYCLE TALLY
-for each acetyl coA entering
the cycle
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
1.3 NAD+ reduced to NADH (6
total = 18 ATP)
2.1 FAD reduced to FADH2 (2
total = 4 ATP)
3.production of 1 GTP (2 total
= 2 ATP in some cells)
4.generation of 2 CO2 (4 total)
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Cellular Respiration = Theoretical Energy
• Glucose contains 686 kcal/mol
• ATP contains 7.3 kcal/mol
• 36 ATP harvested from each molecule of glucose
• 2 from glycolysis – substrate level phosphorylation
• 2 from Kreb’s cycle – converted from GTP (not done by all cells)
• 32 from the ETC & NADH/FADH2
• 2 NADH – glycolysis
• 8 NADH – transition + Kreb’s
• 2 FADH2 – Kreb’s
• note: NADH in the cytosol is only worth 2ATP; NADH in the mitochondria are
worth 3 ATP
• 36 moles of ATP x 7.3 kcal/mol = 263 kcal trapped as ATP
• efficiency : 263/720 = 36% efficiency in converting the potential
energy of glucose into chemical energy
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 their electrons to the electron transport chain
- powers ATP synthesis via oxidative phosphorylation
• donation of electrons to O2 powers the phosphorylation of ADP  ATP
• enzyme of the electron transport chain is in the inner mitochodrial membrane
(cristae)
• most of the chain’s components are multiprotein complexes associated with
carriers
– 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
– the release free energy is broken
up into smaller steps through the
development of separate protein
complexes
• the “fall” is spontaneous as the
uphill complex has a higher G
value vs. the downhill
• as the electrons fall they reduce
the next downhill complex
• eventually O2 is reduced
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• the electron transport chain
generates no ATP directly
• ATP is generated as a result in
the drop of free energy as the
electrons “fall” from one protein
complex to the next
NADH
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• the ETC couples electron
transfer to the generation of
a proton-motive force for
ATP synthesis
NADH
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
– flavoprotein
• Complex II – Succinate
dehydrogenase
– adds additional electrons to the ETC
from succinate via FADH2
• Complex III – Cytochrome bc1
– also know as cytochrome c
reductase
• Complex IV – Cytochrome c
oxidase
• complexes I, II and III have ironsulfur groups (heme groups) that
are critical to their function
NADH
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• four protein complexes coupled
to specific prosthetic groups:
• Complex I – NADH
dehydrogenase
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
NADH
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• Complex I – NADH dehydrogenase
– flavoprotein because one of its
prosthetic groups is flavin
mononucleotide (FMN)
– 4H+ pumped into intermembrane
space
– 1. 2 electrons transferred to FMN 
FMNH2 (reduction in one step)
– 2. Oxidation of FMNH2 (in 2 steps)
 QH2 (ubiquinol)
• the two electrons moved via a FeS group  Q (ubiquinone)
• step A: 1st electron converts Q
 semiquinone
• step B: 2nd electron converts
semiquinone into ubiquinol
(QH2)
• QH2 is lipid soluble and diffuses
through the membrane to
Complex III
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
2 e
10
(originally from
NADH or FADH2)
2 H + 1/2 O2
0
QH2 carries 2
electrons
H2O
•
Complex III – Cytochrome bc1
– transfers its electrons via Q-Cycle
• 4H+ pumped as a result
– QH2 binds to the Qo site on the complex – two electrons
take two pathways:
– path 1. one electron move to Fe-S group and then to a c1
site
• electron then reduces the cytochrome c1 carrier and
then a cytochrome c
– path 2. 2nd electron moves to a cytochrome bL site  a bH
site –> the Qi site of the complex
• a molecule of Q has bound the Qi site – accepts the
electron from bH  becomes the unstable
semiquinone/Q- (not pictured)
• ANOTHER CYCLE IS NEEDED – another QH2 binds the
Qi site – 1st electron reduces the 2nd cyto c and the 2nd
electron travels via bL/bH to reduce semiquinone to
QH2
• this QH2 can cycle back to deliver its electrons to Qo –
continuous cycle
• so 2 cytochrome c’s are reduced and transferred to
Complex IV
This complex can “leak”
electrons to O2 and
create superoxide radicals
(water-soluble &
found in the
intermembrane
space)
THIS PROTEIN COMPLEX
NEEDS 2 MOLECULES OF
QH2 TO RUN (4 electrons)
-moves 4H+
NADH
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• Complex IV – Cytochrome c
Oxidase
– 4 molecules of cyto c deliver
their electrons to this
complex
– 4 electrons are transferred
to cyto a group  cyto a3
group  O2 to create two
molecules of water
– 2 H+ are pumped by this
complex
– water production:
– 2e- + 2H+ + ½ O2  H20
– 4e- + 4H+ + O2  2H20
– this complex can be inhibited
by cyanide
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
NADH
50
2 e
NAD
FADH2
2 e
Free energy (G) relative to O2 (kcal/mol)
• Complex II –Succinate
Dehydrogenase
– transfers the electrons
produced through the
reduction of FAD  FADH2
– 2 electrons moved to Q to
create QH2
40
FMN
FeS
FeS
II
Q
III
Cyt b
30
Multiprotein
complexes
FAD
I
FeS
Cyt c1
IV
Cyt c
Cyt a
20
10
0
Cyt a3
2 e
(originally from
NADH or FADH2)
2 H + 1/2 O2
H2O
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
• 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
H
H
H
Protein
complex
of electron
carriers
Q
I
IV
III
II
FADH2
NADH
H
Cyt c
FAD
2 H + 1/2O2
NAD
ATP
synthase
H2O
ADP  P i
(carrying electrons
from food)
ATP
H
1
Electron transport chain
Oxidative phosphorylation
2
Chemiosmosis
ATP-synthase – comprised of a:
1.stator – two “½ channels” for H+ binding
2.rotor – multiple H+ binding sites
3.internal rod
4.catalytic knob
INTERMEMBRANE SPACE
H
Stator
Rotor
1. H+ ion flowing down its gradient
enters the 1st half-channel in the stator
2. H+ ions enter binding sites within the
rotor
-binding of the H+ ions changes the rotors
Internal
rod
shape so it rotates
3. each H+ ion makes one complete turn
Catalytic
knob
before leaving the rotor and passing through
the second half-channel within the stator
4. spinning of the rotor, rotates the rod and then the
ADP
knob below it
+
5. rotation of the knob activates catalytic sites that
Pi
add a P group to ADP
ATP
MITOCHONDRIAL MATRIX
http://www.youtube.com/watch?v=3y1dO4nNaKY
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
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
An Accounting of ATP Production by Cellular Respiration
• There are several reasons why the number of ATP is not known
exactly
– 1. the ratio of NADH molecules to ATP is not a whole number – phosphorylation and
redox are not directly coupled to each other
– 2. NADH made in the cytosol cannot enter the mitochondria
• must use a “shuttle” to take these electrons into the matrix
• number of ATP made depends on whether FAD or NAD+ is used as that shuttle
– 3. use of the proton-motive force can be used for other mitochondrial work
• powers the uptake of pyruvate from the cytosol
• if this motive force was used exclusively for oxidative phosphorylation = 30 to 32 ATP made
Electron shuttles
span membrane
2 NADH
Glycolysis
2 Pyruvate
Glucose
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
6 NADH
2 FADH2
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
 2 ATP
 about 26 or 28 ATP
About
30 or 32 ATP
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
Animation: Fermentation Overview
Right-click slide / select “Play”
© 2011 Pearson Education, Inc.
• 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
– acetylaldehyde  ethanol is catalyzed by Alcohol Dehydrogenase 1
– Alcohol fermentation by yeast is used in brewing, winemaking, and baking
– humans can take the ethanol and convert it back into a sugar using Alcohol
Dehydrogenase  Acetylaldehyde
2 ADP  2 P
Glucose
i
2 ADP 2 P
2 ATP
Glycolysis
Glucose
2 ATP
i
Glycolysis
2 Pyruvate
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 NAD
2 CO2
2 Acetaldehyde
2 NADH
 2 H
2 Lactate
(b) Lactic acid fermentation
2 Pyruvate
• 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
2 ADP  2 P
Glucose
i
2 ADP 2 P
2 ATP
Glycolysis
Glucose
2 ATP
i
Glycolysis
2 Pyruvate
2 NAD
2 Ethanol
(a) Alcohol fermentation
2 NADH
 2 H
2 NAD
2 CO2
2 Acetaldehyde
2 NADH
 2 H
2 Lactate
(b) Lactic acid fermentation
2 Pyruvate
Comparing Fermentation with Anaerobic
and Aerobic Respiration
• all three pathways 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 (i.e. that gets reduced)
• BUT these processes have different final electron
acceptors:
– aerobic respiration – O2
– anaerobic respiration – other atoms
– fermentation - pyruvate or acetaldehyde
• 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 Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
Ethanol,
lactate, or
other products
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Acetyl CoA
Citric
acid
cycle
Glycolysis and the citric acid cycle connect to
many other metabolic pathways
Proteins
Amino
acids
Carbohydrates
Sugars
Fats
GlycerolFatty
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
• about 10 of the 20 amino acids can be made by
converting substrates from the citric acid cycle
– rest are called essential amino acids
• glucose can be made from pyruvate –
gluconeogenesis
• fatty acids can be made from acetyl coA
Regulation of Cellular Respiration via
Feedback Mechanisms
Glucose
• feedback inhibition is the most
common mechanism for control
• if ATP concentration begins to
drop, respiration speeds up
• control of catabolism is based
mainly on regulating the activity
of enzymes at strategic points
in the catabolic pathway
• key point of regulation:
– phosphofructokinase and ATP/AMP +
citrate
– hexokinase
– pyruvate kinase

Inhibits
AMP
Glycolysis
Fructose 6-phosphate Stimulates

Phosphofructokinase

Fructose 1,6-bisphosphate
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation