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CAMPBELL
BIOLOGY
TENTH
EDITION
Reece • Urry • Cain • Wasserman • Minorsky • Jackson
9
Cellular
Respiration and
Fermentation
Lecture Presentation by
Nicole Tunbridge and
Kathleen Fitzpatrick
© 2014 Pearson Education, Inc.
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.
• Respiration has three key pathways: glycolysis,
the citric acid cycle, and oxidative
phosphorylation.
Figure 9.1
Overview: Life Is Work
• Living cells require energy
from outside sources.
• Energy enters most
ecosystems as sunlight and
leaves as heat.
• Photosynthesis generates
oxygen and organic
molecules that the
mitochondria of eukaryotes
(including plants and algae)
use as fuel for cellular
respiration.
• Cells harvest the chemical
energy stored in organic
molecules and use it to
regenerate ATP, the
molecule that drives most
cellular work.
Figure 9.2
© 2014 Pearson Education, Inc.
Catabolic pathways yield energy by
oxidizing organic fuels
• Catabolic metabolic pathways release the energy
stored in complex organic molecules represents
potential energy.
• Enzymes catalyze the systematic degradation of
organic molecules that are rich in energy to
simpler waste products that have less energy.
• Some of the released energy is used to do work;
the rest is dissipated as heat.
• Electron transfer plays a major role in these
pathways.
• Several processes are central to cellular
respiration and related pathways
© 2014 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
• Cellular respiration includes both aerobic and anaerobic
respiration but is often used to refer to aerobic respiration
– Aerobic respiration consumes organic molecules and
O2 and yields ATP is complete degradation of sugar.
– Anaerobic respiration is similar to aerobic respiration
but consumes compounds other than O2
• 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)
686kcal/mole
© 2014 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
• One mole ATP generate ∆G = −7.3 kcal/mol
The Principle of Redox
• Reactions that result in the transfer of one or more
electrons (e−) from one reactant to another are
oxidation-reduction reactions, or redox reactions.
• The loss of electrons from a substance is called
oxidation or is oxidized.
• The addition of electrons to another substance is
called reduction or is reduced (the amount of
positive charge is reduced).
• Adding electrons is called reduction because
negatively charged electrons added to an atom
reduce the amount of positive charge of that atom.
© 2014 Pearson Education, Inc.
Reducing
Agent
Oxidizing
Agent
Xe− + Y

X
+
Ye−
• The formation of table salt from sodium and chloride, Na +
Cl  Na+ + Cl−, is a redox reaction.
• Sodium is oxidized, and chlorine is reduced (its charge
drops from 0 to −1).
• More generally: Xe− + Y  X + Ye−.
• X, the electron donor, is the reducing agent and reduces
Y by donating an electron to it.
• Y, the electron recipient, is the oxidizing agent and
oxidizes X by removing its electron.
• Redox reactions require both a donor and an acceptor.
© 2014 Pearson Education, Inc.
The combustion of methane to form water and carbon dioxide:
Figure 9.3
•
•
•
•
•
When oxygen reacts with the hydrogen from methane to form water, the
electrons of the covalent bonds are drawn closer to the oxygen.
When oxygen reacts with the carbon from methane to form carbon dioxide,
electrons end up farther away from the carbon atom and closer to their new
covalent partners, the oxygen atoms, which are very electronegative.
In effect, the carbon atom has partially “lost” its shared electrons. Thus,
methane has been oxidized.
In effect, each oxygen atom has partially “gained” electrons, and so the
oxygen molecule has been reduced.
Oxygen is very electronegative and is one of the most potent of all oxidizing
agents.
© 2014 Pearson Education, Inc.
Organic fuel molecules are oxidized
during cellular respiration
• Respiration, the oxidation of glucose and other
molecules in food, is a redox process.
– In a series of reactions, glucose is oxidized and oxygen
is reduced.
– The electrons lose potential energy along the way, and
energy is released.
– As hydrogen is transferred from glucose to oxygen, the
energy state of the electron changes.
• In respiration, the oxidation of glucose transfers
electrons to a lower energy state, releasing energy
that becomes available for ATP synthesis.
© 2014 Pearson Education, Inc.
• The main energy foods, carbohydrates and fats,
are reservoirs of electrons associated with
hydrogen.
• These molecules are stable because of the
barrier of activation energy.
• Without this barrier, a food molecule like glucose
would combine almost instantaneously with O2.
• If activation energy is supplied by igniting
glucose, it burns in air, releasing 686 kcal
(2,870 kJ) of heat per mole of glucose (about
180 g).
• This reaction cannot happen at body
temperatures.
• Instead, enzymes within cells lower the barrier of
activation energy, allowing sugar to be oxidized
in a series of steps.
© 2014 Pearson Education, Inc.
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 the coenzyme NAD+ (nicotinamide
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
© 2014 Pearson Education, Inc.
NAD+ trap electrons from glucose
• NAD+ functions as the oxidizing agent in many of
the redox steps during the breakdown of glucose.
• Dehydrogenase enzymes strip two hydrogen
atoms from the substrate (glucose), thus oxidizing
it.
• The enzyme passes two electrons and one proton
to NAD+.
• The other proton is released as H+ to the
surrounding solution.
• By receiving two electrons and only one proton,
NAD+ has its charge neutralized when it is
reduced to NADH.
• Each NADH molecule formed during respiration
represents stored energy.
© 2011 Pearson Education, Inc.
Figure 9.4
2 e− + 2 H+
2 e− + H+
NAD+
Dehydrogenase
NADH
H+
Reduction of NAD+
2[H]
(from food) Oxidation of NADH
Nicotinamide
(oxidized form)
H+
Nicotinamide
(reduced form)
Figure 9.5
H2 + ½ O2
2H
Explosive
release
Free energy, G
Free energy, G
2 H+ + 2 e−
½ O2
+
Controlled
release of
energy
ATP
ATP
ATP
2 e−
½ O2
2 H+
H2O
(a) Uncontrolled reaction
H2O
(b) Cellular respiration
Electrons extracted from glucose and stored in
NADH transferred to oxygen
• Each NADH molecule formed
during respiration represents
stored energy. This energy is
tapped to synthesize ATP as
electrons “fall” down an energy
gradient from NADH to oxygen.
• Cellular respiration uses an
electron transport chain to
break the fall of electrons to
O2 into several steps.
• Electrons released from food
are shuttled by NADH to the
“top” higher-energy end of the
chain.
• At the “bottom” lower-energy
end, oxygen captures the
electrons along with H+ to
form water.
© 2014 Pearson Education, Inc.
The electron transport chain consists of several
molecules primarily proteins built into the inner
membrane of a mitochondrion of eukaryotic cells and
the plasma membrane of aerobically respiring
prokaryotes.
In summary, during cellular respiration, most electrons
travel the following “downhill” route: glucose 
NADH  electron transport chain  oxygen.
The cell uses the energy released from this stepwise electron “fall” to regenerate ATP
Electron transfer from NADH to oxygen is an
exergonic reaction: ∆G = −53 kcal/mol
© 2014 Pearson Education, Inc.
The Stages of Cellular Respiration:
A Preview
• Cellular respiration has three stages:• Glycolysis breaks down glucose into two
molecules of pyruvate. Glycolysis occurs in the
cytosol.
• The Citric Acid Cycle or Kreb’s cycle completes
the breakdown of glucose. The citric acid cycle
occurs in the mitochondrial matrix of eukaryotic
cells or in the cytoplasm of prokaryotes.
• Oxidative Phosphorylation the electron transport
chain accepts electrons from the first 2 stages and
accounts for most of the ATP synthesis because it
is powered by redox reactions. Oxidative
phosphorylation occurs at the inner membrane
of the mitochondrion.
© 2014 Pearson Education, Inc.
Cellular Respiration-3 stages
Electrons
via NADH
GLYCOLYSIS
Glucose
Electrons
via NADH
and FADH2
PYRUVATE
OXIDATION
CITRIC
ACID
CYCLE
Pyruvate
Acetyl CoA
CYTOSOL
MITOCHONDRION
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Figure 9.6
Substrate-level phosphorylation
Figure 9.7
• In substrate –level phosphorylation an enzyme
transfers a phosphate group from a substrate
molecule to ADP.
• Some ATP is also formed directly during glycolysis
and the citric acid cycle by substrate-level
phosphorylation, in which an enzyme transfers a
phosphate group from an organic substrate
molecule to ADP, forming only 4 ATP.
• 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
• For each molecule of glucose degraded to
CO2 and water by respiration, the cell makes
up to 32 molecules of ATP
© 2014 Pearson Education, Inc.
Glycolysis harvests chemical energy by
oxidizing glucose to pyruvate
•
•
Glycolysis (“splitting of sugar”) breaks down 6-carbon
glucose into two molecules of 3-carbon pyruvate
Glycolysisis a 10 step process that occurs in the
cytoplasm and has two major phases:
1. In the energy investment phase, the cell spends
ATP.
2. In the energy payoff phase, this investment is repaid
with interest. ATP is produced by substrate-level
phosphorylation, and NAD+ is reduced to NADH by
electrons released by the oxidation of glucose.
No CO2 is produced during glycolysis.
Glycolysis occurs +/- oxygen.
© 2014 Pearson Education, Inc.
Energy Investment Phase
Figure 9.8
Glucose
2
ATP used
2 ADP + 2 P
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 9.9a
Glycolysis: Energy Investment Phase
Glucose
ATP
Fructose 6-phosphate
Glucose 6-phosphate
ADP
Hexokinase
1
Phosphoglucoisomerase
2
Step 1
Glucose enters the cell and
is phosphorylated by
hexokinase, which
transfers a P group from
ATP to glucose to form
Glucose-6-P.
Step 2
Phosphoglucoisomerase
converts glucose-6phosphate
to its isomer,fructose-6phosphate
Figure 9.9b
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
ATP
Fructose 1,6-bisphosphate
ADP
Phosphofructokinase
3
Aldolase
4
Step 3
Dihydroxyacetone
Glyceraldehyde
Fructokinase
phosphate
3-phosphate
transfers a P group
from ATP tofructose-6phosphate. With P
groups on opposite
To
Isomerase 5
sides, fructose-1,6step 6
biphosphate is ready to
be split in half.
So far 2 molecules of ATP have been used.
Step 4
Aldose cleaves fructose 1,6-biphosphate into two
different 3 carbon sugars:
Dihydroxyacetone phosphate (DHAP) and
Glyceraldehyde-3-phosphate (G3-P)
Step 5
Isomerase catalyzes the reversible conversion between
the 3-carbon sugar isomers. This reaction never
reaches equilibrium because
glyceraldehyde-3-phosphate is used as quickly as it is
formed as a substrate in the subsequent step
in glycolysis.
Figure 9.9c
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
+ 2 H+
2 NAD+
2 ADP
2
2
Triose
phosphate
dehydrogenase
6
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
2 molecules of NADH have been produced and
2 molecules of ATP have been generated.
Step 6
Triose phosphate dehydrogenase catalyzes 2 sequential
reactions while holding glyceraldehyde-3-phosphate in its
active site.
The sugar is oxidized by the transfer of ℮- and H+ to
NAD+. This is a very exergonic redox reaction.
The enzyme uses the released energy to add a P group
to the oxidized substrate. The 2 1,3-bisphosphoglycerate
molecules produced have very high potential energy.
Step 7
Phosphoglycerokinase
The P group added to make 1,3-bisphosphoglycerate in
the previous step is transferred to ADP in an exergonic
reaction, with 2 ATP produced. So the energy made
available by oxidation in step 6 has been used to generate
ATP.
Figure 9.9d
2 more molecules of ATP have been generated
Pyruvate is the final product of the 10 step process of glycolysis
and the initial substrate of the citric acid cycle (if O2 is present)
Glycolysis: Energy Payoff Phase
2 H2O
2
2
Step 8
8
2 ADP
2
Phosphoglyceromutase
3-Phosphoglycerate
2 ATP
Pyruvate
kinase
Enolase
2-Phosphoglycerate
9
2
Phosphoenolpyruvate (PEP)
Step9
Enolase catalyzes a double bond
Phosphoglyceromutase formation in 2-phosphoglycerate
relocates the remaining
yielding phosphoenolpyruvate(PEP).
The electron arrangement of PEP
P group to change
allows it to have high potential
3-phosphoglycerate to
energy. This high potential energy
2-phosphoglycerate.
allows step 10 to occur.
10
Pyruvate
Step 10
Pyruvate Kinase Transfers
a P group from the 2 PEP
molecules formed in step 9
to generate 2 ATP from 2
ADP (substrate-level
phosphorylation).Glucose is
oxidized to Pyruvate
Energy Produced by Glycolysis
• 2 ATP invested in
energy investment
phase (1 and 3 steps)
4 ATP produced in
energy payoff phase (7
and 10 steps).
• Net gain 2 ATP
• Additional energy is
stored as 2 NADH (6
step) which can be
used to make ATP by
oxidative
phosphorylation if O2 is
present.
© 2014 Pearson Education, Inc.
The citric acid cycle completes the energyyielding 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 CoA,
which links the glycolysis to citric acid cycle
• This step is carried out by a multienzyme
complex that catalyses three reactions
© 2014 Pearson Education, Inc.
Pyruvate to Acetyl CoA is an intermediate step
process
Figure 9.10
• Pyruvate enters the mitochondrion via active transport.
• Pyruvate’s carboxyl group is removed and released as CO2 within
the mitochondrion.
• The remaining 2 carbon fragment is oxidized, forming acetate. The
extracted ℮- are transferred to NAD+, and energy is stored as
NADH.
• Coenzyme A (CoA), a sulfur containing compound derived from B
vitamins, is attached to acetate by an unstable bond form Acetyl
CoA. It enters the citric acid cycle.
© 2014 Pearson Education, Inc.
The Citric Acid Cycle
• The citric acid cycle, also called the Krebs cycle, takes
place within the mitochondrial matrix
• 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 cycle oxidizes organic fuel derived from pyruvate,
generating 1 ATP, 3 NADH, and 1 FADH2 per cycle but
it run twice so everything will be double in number.
• The NADH and FADH2 produced by the cycle relay
electrons extracted from food to the electron transport
chain
Copyright © 2014 Pearson Education, Inc.,
Figure 9.11
Pyruvate
CO2
NAD+
CoA
NADH
+ H+
Acetyl CoA
CoA
CoA
Citric
acid
cycle
The citric acid cycle
oxidizes organic fuel
derived from pyruvate
run twice, finally
generating 2 ATP, 6
NADH, and 2 FADH2.
The NADH and FADH2
produced by the cycle
relay electrons
extracted from food to
the electron transport
chain.
2 CO2
3 NAD+
FADH2
3 NADH
FAD
+ 3 H+
ADP + P i
ATP
Fig.9.12a
Acetyl CoA
CoA-SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
Step 1 -Acetyl CoA adds its acetyl group
to oxaloacetate to produce citrate.
Fig.9.12b
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Step 2 -Citrate is converted to its isomer,
isocitrate by the removal of one H2O molecule
and the addition of another H2O molecule.
Fig.9.12c
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
3
NADH
+ H+
CO2
α-Ketoglutarate
Step 3 -Isocitrate is oxidized (reducing NAD+ to NADH)
and the resulting compound loses a CO2 molecule
to form α-ketoglutarate.
Fig.9.12d
Acetyl CoA
CoA-SH
H2O
1
Step 4 -Another CO2 is
lost and the resulting
compound is oxidized.
This reduces NAD+ to
NADH. CoA is then
attached to the resulting
molecule by an unstable
bond to form
SuccinylCoA.
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
3
+ H+
CO2
CoA-SH
α-Ketoglutarate
4
NAD+
NADH
Succinyl
CoA
+ H+
CO2
Fig.9.12e
Step 5 -A P group
displaces the CoA. Then
the P group is transferred
to guanosine diphosphate
(GDP) forming GTP. GTP
can be used to make an
ATP molecule or GTP can
power cellular work.
Succinate is produced
when the P group is
transferred to GDP.
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
NADH
3
+ H+
CO2
CoA-SH
α-Ketoglutarate
4
CoA-SH
5
NAD+
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig.9.12f
Acetyl CoA
Step 6 - 2 hydrogens
are transferred
to FAD (flavin
dinucleotide),
forming FADH2 and
oxidizing
succinate to form
fumarate.
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD+
Citric
acid
cycle
Fumarate
NADH
3
+ H+
CO2
CoA-SH
α-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig.9.12g
Step 7- H2O is added,
converting fumarate
to malate.
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H+
CO2
CoA-SH
α-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
Fig.9.11h
Step 8- Malate is
oxidized to
oxaloacetate
which can reenter the cycle
for another
round. NAD+ is
reduced to
NADH.
Acetyl CoA
CoA-SH
NADH
+ H+
H2O
1
NAD+
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD+
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H+
CO2
CoA-SH
α-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD+
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H+
CO2
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
© 2014 Pearson Education, Inc.
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,
which combine with H of NADH or FADH2
to form H2O
© 2014 Pearson Education, Inc.
Figure 9.13
NADH
50
2 e−
NAD+
FADH2
Free energy (G) relative to O2 (kcal/mol)
2 e−
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
• 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
• 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
© 2014 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 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
© 2014 Pearson Education, Inc.
Figure 9.14
INTERMEMBRANE
H+
SPACE
Rotor
Stator
Internal rod
Catalytic
knob
ADP
+
Pi
MITOCHONDRIAL
MATRIX
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 protonmotive force, emphasizing its capacity to
do work
© 2014 Pearson Education, Inc.
Figure 9.15
Protein
complex
of electron
carriers
H+
H+
Cyt c
IV
Q
III
I
II
FADH2 FAD
NADH
(carrying
electrons
from
food)
ATP
synthase
H+
H+
2 H+ + ½ O2
NAD+
H2O
ADP + P i
ATP
H+
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
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 38 ATP
• There are several reasons why the number
of ATP is not known exactly
© 2014 Pearson Education, Inc.
Figure 9.16
Electron shuttles
span membrane
CYTOSOL
2 NADH
6 NADH
2 NADH
GLYCOLYSIS
Glucose
MITOCHONDRION
2 NADH
or
2 FADH2
2
Pyruvate
PYRUVATE
OXIDATION
2 Acetyl CoA
+ 2 ATP
Maximum per glucose:
2 FADH2
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron transport
and chemiosmosis)
+ 2 ATP
+ about 26 or 28 ATP
About
30 or 32 ATP
1NADH makes 3ATP and 1FADH2 makes 2ATP
10NADH = 10X3ATP=30ATP and 2FADH2 = 2X2ATP= 4ATP.
Finally 28ATP+4ATP= 32ATP in eukaryotes but prokaryotes has more 30+4ATP= 34ATP
by oxidative phosphorylation. Only 2ATP from glycolysis and 2ATP from citric acid cycle.
Total #ATP generate by eukaryotes 2+2+32 =36ATP and by prokaryote 2+2+34=38ATP.
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
• Anaerobic respiration uses an electron transport
chain with an electron acceptor other than O2, for
example sulfate or nitrate
• Fermentation uses substrate level phosphorylation
instead of an electron transport chain to generate ATP
© 2014 Pearson Education, Inc.
Two types of Fermentation
Fermentation consists of glycolysis plus reactions that
regenerate NAD+, which can be reused by glycolysis
Two common types areAlcohol fermentation and Lactic acid fermentation.
© 2014 Pearson Education, Inc.
In alcohol fermentation, pyruvate is
converted to ethanol in two steps
• The first step releases CO2
• The second step produces ethanol
Alcohol fermentation by yeast is used in
brewing, winemaking, and baking
© 2014 Pearson Education, Inc.
Figure 9-17a
2 ADP + 2 P
Glucose
i
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 NADH
2 CO2
+ 2 H+
2 Ethanol
(a) Alcohol fermentation
2 Acetaldehyde
• 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
© 2014 Pearson Education, Inc.
Figure 9-17 b
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
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 36 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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Figure 9.18
Glucose
CYTOSOL
Glycolysis
Pyruvate
No O2 present:
Fermentation
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
CITRIC
ACID
CYCLE
The Evolutionary Significance of Glycolysis
• Ancient prokaryotes are thought to have
used glycolysis long before there was
oxygen in the atmosphere
• Very little O2 was available in the
atmosphere until about 2.7 billion years
ago, so early prokaryotes likely used
only glycolysis to generate ATP
• Glycolysis is a very ancient process
• Glycolysis occurs in nearly all organisms
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Glycolysis and the citric acid cycle
connect to many other metabolic pathways
• Gycolysis and the citric acid cycle are major
intersections to various catabolic and
anabolic pathways
The Versatility of Catabolism
• Catabolic pathways funnel electrons from
many kinds of organic molecules into
cellular respiration
• Glycolysis accepts a wide range of
carbohydrates
• Proteins must be digested to amino
acids; amino groups can feed glycolysis
or the citric acid cycle
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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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Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Fatty
acids
GLYCOLYSIS
Glucose
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
CITRIC
ACID
CYCLE
Figure 9.19
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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Figure 9.20
Glucose
GLYCOLYSIS
Fructose 6-phosphate
AMP
Stimulates
Phosphofructokinase
Fructose 1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
CITRIC
ACID
CYCLE
Oxidative
phosphorylation
Outputs
Inputs
Glycolysis
Glucose
2 Pyruvate + 2
+ 2 NADH
ATP
Outputs
Inputs
2 Pyruvate
2 Acetyl CoA
2 Oxaloacetate
Citric
acid
cycle
NADH
2
ATP
8
6
CO2
2 FADH2
Overview Cellular Respiration