Download NVC Bio 120 lect 9 cell respiration

9/25/2011
Chapter 9 – Cellular Respiration and
Fermentation
Overview: Life Is Work
 Living cells require energy from outside sources
 Some animals, 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
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Figure 9.2
Catabolic pathways yield energy by oxidizing organic fuels
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
CO2  H2O
Cellular respiration
in mitochondria
ATP
Organic
 O2
molecules
 Several processes are central to cellular
respiration and related pathways
ATP powers
most cellular work
Heat
energy
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Catabolic Pathways and Production of ATP
 The breakdown of organic molecules is exergonic
 Fermentation is a partial degradation of sugars
that occurs without O2
 Aerobic respiration consumes organic
molecules and O2 and yields ATP
 Anaerobic respiration is similar to aerobic
respiration but consumes compounds other than
O2
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Cellular Respiration
 Cellular respiration includes both aerobic and
anaerobic respiration but is often used to refer
to aerobic respiration
 Although carbohydrates, fats, and proteins are
all consumed as fuel, it is helpful to trace
cellular respiration with the sugar glucose
C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP +
heat)
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Redox Reactions: Oxidation and Reduction
 The transfer of electrons during chemical reactions
releases energy stored in organic molecules
 This released energy is ultimately used to
synthesize ATP
The Principle of Redox
 Chemical reactions that transfer electrons
between reactants are called oxidation-reduction
reactions, or redox reactions
• In oxidation, a substance loses electrons, or is
oxidized
 In reduction, a substance gains electrons, or is
reduced (the amount of positive charge is
reduced)
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Figure 9.UN01
 The electron donor is called the reducing agent
 The electron receptor is called the oxidizing
agent
becomes oxidized
(loses electron)
becomes reduced
(gains electron)
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Oxidation of Organic Fuel Molecules During Cellular
Respiration
Figure 9.UN03
 During cellular respiration, the fuel (such as
glucose) is oxidized, and O2 is reduced
becomes oxidized
becomes reduced
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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
Figure 9.4
NAD
NADH
Dehydrogenase
Reduction of NAD 
(from food)
 Electrons from organic compounds are usually first
transferred to NAD+, a coenzyme
Nicotinamide
(oxidized form)
Oxidation of NADH
Nicotinamide
(reduced form)
 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
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Figure 9.UN04
The Role of NADH in Cellular Respiration
 NADH passes the electrons to the electron
transport chain
Dehydrogenase
 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 energyyielding tumble
 The energy yielded is used to regenerate ATP
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Figure 9.5
The Stages of Cellular Respiration: A Preview
Free energy, G
Free energy, G
H2  1/2 O2
Explosive
release of
heat and light
energy
1/ O

2H
2
2
(from food via NADH)
Controlled
release of
2 H+  2 e
energy for
synthesis of
ATP
ATP
 Glycolysis (breaks down glucose into two
molecules of pyruvate)
ATP
 The pyruvate oxidation and citric acid cycle
(completes the breakdown of glucose)
ATP
2
e
1/
2
2 H+
H2 O
O2
H2 O
(a) Uncontrolled reaction
 Harvesting of energy from glucose has three stages
 Oxidative phosphorylation (accounts for most of
the ATP synthesis)
(b) Cellular respiration
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Figure 9.UN05
Figure 9.6-1
Electrons
carried
via NADH
1. Glycolysis (color-coded teal throughout the chapter)
2. Pyruvate oxidation and the citric acid cycle
(color-coded salmon)
3. Oxidative phosphorylation: electron transport and
chemiosmosis (color-coded violet)
Glycolysis
Glucose
Pyruvate
MITOCHONDRION
CYTOSOL
ATP
Substrate-level
phosphorylation
Figure 9.6-2
Figure 9.6-3
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
CYTOSOL
Pyruvate
oxidation
Acetyl CoA
Citric
acid
cycle
MITOCHONDRION
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
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
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Oxidative Phosphorylation
 The process that generates most of the ATP is
called oxidative phosphorylation because it is
powered by redox reactions
BioFlix: Cellular Respiration
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Substrate-level Phosphorylation
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Figure 9.7
 Oxidative phosphorylation accounts for almost
90% of the ATP generated by cellular
respiration
Enzyme
 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
Enzyme
ADP
P
Substrate
ATP
Product
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Glycolysis harvests chemical energy by oxidizing
glucose to pyruvate
Figure 9.8
Energy Investment Phase
Glucose
2 ADP  2 P
 Glycolysis (“splitting of sugar”) breaks down
glucose into two molecules of pyruvate
 Glycolysis occurs in the cytoplasm and has two
major phases
Energy Payoff Phase
4 ADP  4 P
 Energy investment phase
 Energy payoff phase
 Glycolysis occurs whether or not O2 is present
2 ATP used
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+
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Figure 9.9a
Figure 9.9b
Glycolysis: Energy Investment Phase
Fructose 6-phosphate
Glycolysis: Energy Investment Phase
Glucose
ATP
Glucose 6-phosphate
ADP
ATP
Fructose 1,6-bisphosphate
ADP
Phosphofructokinase
Fructose 6-phosphate
Aldolase
3
Hexokinase
Phosphoglucoisomerase
1
Dihydroxyacetone
phosphate
2
Glyceraldehyde
3-phosphate
Isomerase
Figure 9.9c
4
To
step 6
5
Figure 9.9d
Glycolysis: Energy Payoff Phase
Glycolysis: Energy Payoff Phase
2 ATP
2 NADH
2 NAD
+2
2 H2O
2 ADP
H
2
2
2
2 ATP
2 ADP
2
2
2
Triose
phosphate
dehydrogenase
6
Phosphoglyceromutase
Phosphoglycerokinase
2Pi
1,3-Bisphosphoglycerate
7
3-Phosphoglycerate
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
3-Phosphoglycerate
8
Enolase
2-Phosphoglycerate
9
Pyruvate
kinase
Phosphoenolpyruvate (PEP)
10
Pyruvate
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
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Coenzyme A
Figure 9.10
MITOCHONDRION
CYTOSOL
CO2
Coenzyme A
1
3
2
NADH + H
NAD
Pyruvate
Acetyl CoA
Transport protein
The Citric Acid Cycle
Figure 9.11
Pyruvate
CO2
NAD
CoA
 The citric acid cycle, also called the Krebs cycle,
completes the break down of pyruvate to CO2
NADH
+
H
Acetyl CoA
CoA
CoA
 The cycle oxidizes organic fuel derived from
pyruvate, generating 1 ATP, 3 NADH, and 1
FADH2 per turn, there will be two turns for every
glucose that went into glycolysis
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
+ 3 H
ADP + P i
ATP
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The Citric Acid Cycle
Figure 9.12-1
Acetyl CoA
• The citric acid cycle has eight steps, each
catalyzed by a specific enzyme
CoA-SH
1
Oxaloacetate
• 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
Citrate
Citric
acid
cycle
• The NADH and FADH2 produced by the cycle
relay electrons extracted from food to the electron
transport chain
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Figure 9.12-2
Figure 9.12-3
Acetyl CoA
Acetyl CoA
CoA-SH
CoA-SH
H2O
1
H2O
1
Oxaloacetate
Oxaloacetate
2
2
Citrate
Citrate
Isocitrate
Isocitrate
NAD
Citric
acid
cycle
Citric
acid
cycle
NADH
3
+ H
CO2
 -Ketoglutarate
Figure 9.12-4
Figure 9.12-5
Acetyl CoA
Acetyl CoA
CoA-SH
CoA-SH
H2O
1
H2O
1
Oxaloacetate
Oxaloacetate
2
2
Citrate
Citrate
Isocitrate
Isocitrate
NAD
Citric
acid
cycle
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
NADH
3
+ H
CO2
CoA-SH
CoA-SH
 -Ketoglutarate
 -Ketoglutarate
4
4
CoA-SH
5
CO2
NAD
Succinate
+ H
Succinyl
CoA
CO2
NAD
NADH
NADH
Pi
GTP GDP
+ H
Succinyl
CoA
ADP
ATP
Figure 9.12-6
Figure 9.12-7
Acetyl CoA
Acetyl CoA
CoA-SH
CoA-SH
H2O
1
H2O
1
Oxaloacetate
Oxaloacetate
2
2
Malate
Citrate
Citrate
Isocitrate
Isocitrate
NAD
Citric
acid
cycle
Fumarate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
7
H2O
Fumarate
CoA-SH
CoA-SH
 -Ketoglutarate
4
5
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
4
6
CoA-SH
FADH2
NADH
+ H
CO2
+ H
CO2
 -Ketoglutarate
6
NADH
3
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
Pi
Succinyl
CoA
CO2
NADH
+ H
ADP
ATP
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Figure 9.12-8
Figure 9.12a
Acetyl CoA
CoA-SH
NADH
H2O
1
+ H
Acetyl CoA
NAD
Oxaloacetate
8
2
Malate
CoA-SH
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
NADH
3
+ H
CO2
Fumarate
H2O
1
CoA-SH
 -Ketoglutarate
Oxaloacetate
4
6
CoA-SH
2
5
FADH2
NAD
FAD
Succinate
NADH
Pi
+ H
Succinyl
CoA
GTP GDP
CO2
Citrate
ADP
Isocitrate
ATP
Figure 9.12b
Figure 9.12c
Fumarate
Isocitrate
NAD
6
NADH
3
CoA-SH
+ H
CO2
5
FADH2
FAD
CoA-SH
-Ketoglutarate
Succinate
4
Pi
GTP GDP
CO2
NAD
Succinyl
CoA
ADP
NADH
ATP
+ H
Succinyl
CoA
Figure 9.12d
During oxidative phosphorylation, chemiosmosis
couples electron transport to ATP synthesis
NADH
+ H
NAD
8
Oxaloacetate
• NADH and FADH2 account for most of the energy
extracted from food
Malate
• These two electron carriers donate electrons to the
electron transport chain, which powers ATP
synthesis via oxidative phosphorylation
7
H2O
Fumarate
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Figure 9.13
The Pathway of Electron Transport
NADH
50
2 e
 The electron transport chain is in the inner
membrane (cristae) of the mitochondrion
NAD
FADH2
Free energy (G) relative to O2 (kcal/mol)
2 e
 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
40
Multiprotein
complexes
FAD
I
FMN
Fe  S
Fe  S
II
Q
III
Cyt b
Fe  S
30
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
20
2 e
10
(originally from
NADH or FADH2)
2 H + 1/2 O2
0
H2 O
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Chemiosmosis: The Energy-Coupling Mechanism
The Pathway of Electron Transport
 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
 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
 The electron transport chain generates no ATP
directly
 ATP synthase uses the exergonic flow of H+ to
drive phosphorylation of ATP
 It breaks the large free-energy drop from food to
O2 into smaller steps that release energy in
manageable amounts
 This is an example of chemiosmosis, the use of
energy in a H+ gradient to drive cellular work
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Figure 9.15
Figure 9.14
INTERMEMBRANE SPACE
H
Stator
H
H
Rotor

H
Protein
complex
of electron
carriers
Q
I
IV
III
II
FADH2 FAD
NADH
H
Cyt c
2 H + 1/2O2
ATP
synthase
H2O
NAD
ADP  P i
(carrying electrons
from food)
ATP
Internal
rod
Catalytic
knob
H
1 Electron transport chain
Oxidative phosphorylation
2 Chemiosmosis
ADP
+
Pi
ATP
MITOCHONDRIAL MATRIX
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 The energy stored in a H+ gradient across a
membrane couples the redox reactions of the
electron transport chain to ATP synthesis
 The H+ gradient is referred to as a proton-motive
force, emphasizing its capacity to do work
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An Accounting of ATP Production by Cellular
Respiration
Figure 9.16
Electron shuttles
span membrane
 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
2 NADH
Glycolysis
Glucose
2 Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
Pyruvate oxidation
2 Acetyl CoA
 2 ATP
Maximum per glucose:
 There are several reasons why the number of ATP
is not known exactly
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
CYTOSOL
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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 and Fermentation
Types of Fermentation
 Anaerobic respiration uses an electron
transport chain with a final electron acceptor
other than O2, for example sulfate
 Fermentation consists of glycolysis plus reactions
that regenerate NAD+, which can be reused by
glycolysis
 Fermentation uses substrate-level
phosphorylation instead of an electron transport
chain to generate ATP
 Two common types are alcohol fermentation and
lactic acid fermentation
 Which is used by yeast?
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Alcohol Fermentation
 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
Animation: Fermentation Overview
Right-click slide / select “Play”
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Figure 9.17a
Lactic Acid Fermentation
2 ADP  2 P i
Glucose
2 ATP
 In lactic acid fermentation, pyruvate is reduced
to NADH, forming lactate as an end product,
with no release of CO2
Glycolysis
2 Pyruvate
2 NAD 
2 NADH
 2 H
2 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 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
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Figure 9.17b
2 ADP  2 P i
Glucose
Comparing Fermentation with Anaerobic and
Aerobic Respiration
2 ATP
Glycolysis
2 NAD 
2 NADH
 2 H
2 Pyruvate
2 Lactate
 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
(b) Lactic acid fermentation
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Figure 9.18
 Obligate anaerobes carry out fermentation or
anaerobic respiration and cannot survive in the
presence of O2
Glucose
CYTOSOL
Pyruvate
No O2 present:
Fermentation
 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
Glycolysis
O2 present:
Aerobic cellular
respiration
MITOCHONDRION
Ethanol,
lactate, or
other products
Acetyl CoA
Citric
acid
cycle
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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 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
 Glycolysis is a very ancient process
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The Versatility of Catabolism
 Catabolic pathways funnel electrons from many
kinds of organic molecules into cellular
respiration
 Fats are digested to glycerol (used in glycolysis)
and fatty acids (used in generating acetyl CoA)
 Glycolysis accepts a wide range of
carbohydrates
 Fatty acids are broken down by oxidation and
yield acetyl CoA
 Proteins must be digested to amino acids;
amino groups can feed glycolysis or the citric
acid cycle
 An oxidized gram of fat produces more than
twice as much ATP as an oxidized gram of
carbohydrate
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Figure 9.19
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Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Biosynthesis (Anabolic Pathways)
Glycerol Fatty
acids
Glycolysis
Glucose
 The body uses small molecules to build other
substances
Glyceraldehyde 3- P
NH3
Pyruvate
Acetyl CoA
 These small molecules may come directly
from food, from glycolysis, or from the citric
acid cycle
Citric
acid
cycle
Oxidative
phosphorylation
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Regulation of Cellular Respiration via Feedback
Mechanisms
 Feedback inhibition is the most common
mechanism for control
Figure 9.20
Glucose
AMP
Glycolysis
Fructose 6-phosphate

Phosphofructokinase

Fructose 1,6-bisphosphate
Inhibits
Inhibits
 If ATP concentration begins to drop, respiration
speeds up; when there is plenty of ATP,
respiration slows down
Pyruvate
ATP
 Control of catabolism is based mainly on
regulating the activity of enzymes at strategic
points in the catabolic pathway
Stimulates

Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
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Figure 9.UN07
Oxidation
of Pyruvate to Acetyl CoA and Citric Acid Cycle
Glycolysis
Glycolysis
Outputs
Inputs
Inputs
Outputs
2 Pyruvate
2 Acetyl CoA
Glycolysis
Glucose
2 Pyruvate  2
ATP
 2 NADH
2 Oxaloacetate
2
ATP
8 NADH
6
CO2
2 FADH2
Citric
acid
cycle
Summary of Cellular Respiration
 VCAC: Cellular Processes: Electron
Transport Chain
 One molecule of glucose is broken down
and 32 - 38 ATP are generated.
 Oxygen is used by the electron transport
chain
 Carbon dioxide is produced by the Transition
Reaction Krebs cycle
Summary of Cellular Respiration
 Glycolysis: Starts the process by taking in
glucose. Produces 2 ATP
 The Pyruvate Oxidation produces CO2 and
NADH
 The Citric acid cycle: Gives 2 ATP but also
produces lots of NADH and FADH2. Produces
CO2.
Summary of Cellular Respiration
 Electron transport chain
 Takes electrons from NADH and FADH2
and uses them to produce ATP using the
ATP synthase molecule.
 Requires oxygen. Oxygen is the final
electron acceptor on the electron
transport chain
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Which stage produces CO2
Which stage uses O2
Tr
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Which stage produces the most ATP
1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Chain
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33% 33% 33%
or
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33% 33% 33%
ly
si
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Which stage produces the most NADHs
1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Chain
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1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Chain
or
t.
..
C
bs
ly
co
ly
si
s
yc
le
33% 33% 33%
G
1. Glycolysis
2. Krebs Cycle
3. Electron Transport
Chain
Which process requires oxygen?
Glucose is the only molecule that can be broken down for energy in
cellular respiration
at
io
en
t
sp
Fe
rm
re
bi
c
ce
llu
la
r
ce
llu
la
r
er
o
A
na
er
ob
ic
A
ls
e
Fa
ue
Tr
n
33% 33% 33%
1. Anaerobic cellular
respiration
2. Aerobic cellular
respiration
3. Fermentation
re
s.
..
50%
i..
.
50%
1. True
2. False
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9/25/2011
Important Concepts
 Know what Aerobic Cellular respiration, Anaerobic
cellular respiration and Anaerobic Fermentation
are and the differences between them.
 Know the overall reaction of aerobic cellular
respiration and what molecule is oxidized and what
is reduced
 Know the four steps of aerobic cellular respiration,
what happens in each step, what is the starting
molecules are, what comes out of each step,
where in the cell does each step occur. How many
ATP, NADH and FADH2 are produced in each step
Important Concepts
 What is the role of NADH and FADH2
 How is ATP made in the ETC, what is the role of
ATPsynthase?
 Know the overall picture of cellular respiration
 What is the role of oxygen in cellular respiration,
what steps produce carbon dioxide
 Know Anaerobic Fermentation, what happens,
what are the end products, when is it used, what
organisms use it and the different reactions
depending on the organisms (ie yeast vs
animals).
17