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Chapter 6
Cellular Respiration: Obtaining
Energy from Food
PowerPoint® Lectures for
Campbell Essential Biology, Fourth Edition
– Eric Simon, Jane Reece, and Jean Dickey
Campbell Essential Biology with Physiology, Third Edition
– Eric Simon, Jane Reece, and Jean Dickey
Lectures by Chris C. Romero, updated by Edward J. Zalisko
© 2010 Pearson Education, Inc.
Biology and Society:
Marathoners versus Sprinters
• Sprinters do not usually compete at short and long distances.
• Natural differences in the muscles of these athletes favor sprinting
or long-distance running.
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• The muscles that move our legs contain two main types of muscle
fibers:
• Slow-twitch fibers:
– Generate less power
– Last longer
– Generate ATP using oxygen
• Fast-twitch fibers:
– Generate more power
– Fatigue much more quickly
– Can generate ATP without using oxygen
• All human muscles contain both types of fibers but in different ratios.
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ENERGY FLOW AND CHEMICAL CYCLING
IN THE BIOSPHERE
• Animals depend on plants to convert solar energy to:
– Chemical energy of sugars
– Other molecules we consume as food
• Photosynthesis:
– Uses light energy from the sun to power a chemical process that makes
organic molecules.
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Producers and Consumers
• Plants and other autotrophs (self-feeders):
– Make their own organic matter from inorganic nutrients.
• Heterotrophs (other-feeders):
– Include humans and other animals that cannot make organic molecules
from inorganic ones.
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Chemical Cycling between Photosynthesis and
Cellular Respiration
• The ingredients for photosynthesis are carbon dioxide and water.
– CO2 is obtained from the air by a plant’s leaves.
– H2O is obtained from the damp soil by a plant’s roots.
• Chloroplasts in the cells of leaves:
– Use light energy to rearrange the atoms of CO2 and H2O, which produces
–
Sugars (such as glucose)
–
Other organic molecules
–
Oxygen
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• Plant and animal cells perform cellular respiration, a chemical
process that:
– Primarily occurs in mitochondria
– Harvests energy stored in organic molecules
– Uses oxygen
– Generates ATP
• The waste products of cellular respiration are:
– CO2 and H2O
– Used in photosynthesis
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• Animals perform only cellular respiration.
• Plants perform:
– Photosynthesis and
– Cellular respiration
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Sunlight energy
enters ecosystem
C6H12O6
Photosynthesis
CO2
Glucose
Carbon dioxide
O2
Oxygen
H2O
Water
Cellular respiration
ATP drives cellular work
Heat energy exits ecosystem
Figure 6.2
CELLULAR RESPIRATION:
AEROBIC HARVEST OF FOOD ENERGY
• Cellular respiration is:
– The main way that chemical energy is harvested from food and converted
to ATP
– An aerobic process—it requires oxygen
• Cellular respiration and breathing are closely related.
– Cellular respiration requires a cell to exchange gases with its
surroundings.
–
Cells take in oxygen gas.
–
Cells release waste carbon dioxide gas.
– Breathing exchanges these same gases between the blood and outside air.
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O2
CO2
Breathing
Lungs
CO2
O2
Cellular
respiration
Muscle
cells
Figure 6.3
O2
CO2
Breathing
Lungs
CO2
O2
Cellular
respiration
Muscle
cells
Figure 6.3a
The Overall Equation for Cellular Respiration
• A common fuel molecule for cellular respiration is glucose.
• The overall equation for what happens to glucose during cellular
respiration:
Oxidation
Glucose loses electrons
(and hydrogens)
C6H12O6
Glucose
 6
O2
Oxygen
6
CO2
Carbon
dioxide
 6
H 2O
Water
Reduction
Oxygen gains electrons (and hydrogens)
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The Role of Oxygen in Cellular Respiration
• Cellular respiration can produce up to 38 ATP molecules for each
glucose molecule consumed.
• During cellular respiration, hydrogen and its bonding electrons
change partners.
– Hydrogen and its electrons go from sugar to oxygen, forming water.
– This hydrogen transfer is why oxygen is so vital to cellular respiration.
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Redox Reactions
• Chemical reactions that transfer electrons from one substance to
another are called:
– Oxidation-reduction reactions or Redox reactions for short
• The loss of electrons during a redox reaction is called oxidation.
• The acceptance of electrons during a redox reaction is called
reduction.
• During cellular respiration glucose is oxidized while oxygen is
reduced.
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Glycolysis
Citric
Acid
Cycle
ATP
ATP
Electron
Transport
ATP
Figure 6.UN03
• Why does electron transfer to oxygen release energy?
– When electrons move from glucose to oxygen, it is as though the
electrons were falling.
– This “fall” of electrons releases energy during cellular respiration.
• Cellular respiration is:
– A controlled fall of electrons
– A stepwise cascade much like going down a staircase
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1
2 O2
H2
Release
of heat
energy
H 2O
Figure 6.4
NADH and Electron Transport Chains
• The path that electrons take on their way down from glucose to
oxygen involves many steps.
• The first step is an electron acceptor called NAD+.
– The transfer of electrons from organic fuel to NAD+ reduces it to NADH.
• The rest of the path consists of an electron transport chain,
which:
– Involves a series of redox reactions
– Ultimately leads to the production of large amounts of ATP
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e e Electrons from food
e e
NADH
NAD
2 H
Stepwise release
of energy used
to make
ATP
2 e
2 e
2 H
1
2
O2
Hydrogen, electrons, H2O
and oxygen combine
to produce water
Figure 6.5
An Overview of Cellular Respiration
• Cellular respiration:
– Is an example of a metabolic pathway, which is a series of chemical
reactions in cells
• All of the reactions involved in cellular respiration can be
grouped into three main stages:
– Glycolysis
– The citric acid cycle
– Electron transport
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Cytoplasm
Mitochondrion
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
2
Pyruvic
acid
ATP
High-energy
electrons carried
mainly by
NADH
Citric
Acid
Cycle
Electron
Transport
ATP
ATP
Figure 6.6a
The Three Stages of Cellular Respiration
• With the big-picture view of cellular respiration in mind, let’s
examine the process in more detail.
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Stage 1: Glycolysis
• A six-carbon glucose molecule is split in half to form two
molecules of pyruvic acid.
• These two molecules then donate high energy electrons to NAD+,
forming NADH.
• Glycolysis:
– Uses two ATP molecules per glucose to split the six-carbon glucose
– Makes four additional ATP directly when enzymes transfer phosphate
groups from fuel molecules to ADP
• Thus, glycolysis produces a net of two molecules of ATP per
glucose molecule.
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INPUT
OUTPUT
NADH
NAD
2 ATP
2 ADP
2 ATP
2 ADP
2 Pyruvic acid
Glucose
Key
Carbon atom
Phosphate
group
High-energy
electron
2 ADP
NAD
2 ATP
NADH
Energy investment phase
Energy harvest phase
Figure 6.7-3
Enzyme
P
P
ADP
ATP
P
Figure 6.8
Stage 2: The Citric Acid Cycle
• The citric acid cycle completes the breakdown of sugar.
• In the citric acid cycle, pyruvic acid from glycolysis is first
“prepped.”
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INPUT
OUTPUT
Oxidation of the fuel
generates NADH
(from glycolysis)
NAD
(to citric acid cycle)
NADH
CoA
Pyruvic acid
Pyruvic acid
loses a carbon
as CO2
Acetic acid
CO2
Coenzyme A
Acetic acid
attaches to
coenzyme A
Acetyl CoA
Figure 6.9
• The citric acid cycle:
– Extracts the energy of sugar by breaking the acetic acid molecules all the
way down to CO2
– Uses some of this energy to make ATP
– Forms NADH and FADH2
© 2010 Pearson Education, Inc.
INPUT
OUTPUT
Citric
acid
Acetic
acid
2 CO2
ADP  P
ATP
Citric
Acid
Cycle
3
NAD
3
FAD
NADH
FADH2
Acceptor
molecule
Figure 6.10
Stage 3: Electron Transport
• Electron transport releases the energy your cells need to make the
most of their ATP.
• The molecules of the electron transport chain are built into the
inner membranes of mitochondria.
– The chain functions as a chemical machine that uses energy released by
the “fall” of electrons to pump hydrogen ions across the inner
mitochondrial membrane.
– These ions store potential energy.
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• When the hydrogen ions flow back through the membrane, they
release energy.
– The hydrogen ions flow through ATP synthase.
– ATP synthase:
–
Takes the energy from this flow
–
Synthesizes ATP
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Space
between
H
membranes
Electron
carrier
Protein
complex
H
H
H
H
H
FADH2
FAD
H
H
H
H
H
H
H
Inner
mitochondrial
membrane
Electron
flow
1
2
NADH
H
Matrix
H
NAD
H
O2  2 H
H2O
ADP  P
H
Electron transport chain
H
ATP
H
ATP synthase
Figure 6.11a
• Cyanide is a deadly poison that:
– Binds to one of the protein complexes in the electron transport chain
– Prevents the passage of electrons to oxygen
– Stops the production of ATP
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The Versatility of Cellular Respiration
• In addition to glucose, cellular respiration can “burn”:
– Diverse types of carbohydrates
– Fats
– Proteins
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Food
Polysaccharides
Sugars
Fats
Glycerol Fatty acids
Glycolysis
Acetyl
CoA
Proteins
Amino acids
Citric
Acid
Cycle
Electron
Transport
ATP
Figure 6.12
Cytoplasm
Mitochondrion
2
NADH
Glycolysis
Glucose
2
Pyruvic
acid
2
NADH
2
Acetyl
CoA
6
NADH
2
FADH2
Citric
Acid
Cycle
2
ATP
2
ATP
by direct
synthesis
by direct
synthesis
Electron
Transport
Maximum
per
glucose:
About
34 ATP
About
38 ATP
by ATP
synthase
Figure 6.13
FERMENTATION: ANAEROBIC HARVEST
OF FOOD ENERGY
• Some of your cells can actually work for short periods without
oxygen.
• Fermentation is the anaerobic (without oxygen) harvest of food
energy.
• After functioning anaerobically for about 15 seconds:
– Muscle cells will begin to generate ATP by the process of fermentation
• Fermentation relies on glycolysis to produce ATP.
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• Glycolysis:
– Does not require oxygen
– Produces two ATP molecules for each glucose broken down to pyruvic
acid
• Pyruvic acid, produced by glycolysis, is
– Reduced by NADH, producing NAD+, which keeps glycolysis going.
• In human muscle cells, lactic acid is a by-product.
© 2010 Pearson Education, Inc.
INPUT
2 ADP
2 P
OUTPUT
2 ATP
Glycolysis
2 NAD 2 NADH
Glucose
2 NADH 2 NAD
2 Pyruvic
H

2
acid
2 Lactic acid
Figure 6.14a
The Process of Science:
Does Lactic Acid Buildup Cause Muscle Burn?
• Observation: Muscles produce lactic acid under anaerobic
conditions.
• Question: Does the buildup of lactic acid cause muscle fatigue?
• Hypothesis: The buildup of lactic acid would cause muscle
activity to stop.
• Experiment: Tested frog muscles under conditions when lactic
acid could and could not diffuse away.
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Battery
Battery
Force
measured
Force
measured
Frog muscle
stimulated by
electric current
Solution prevents
diffusion of lactic acid
Solution allows
diffusion of lactic acid;
muscle can work for
twice as long
Figure 6.15
• Results: When lactic acid could diffuse away, performance
improved greatly.
• Conclusion: Lactic acid accumulation is the primary cause of
failure in muscle tissue.
• However, recent evidence suggests that the role of lactic acid in
muscle function remains unclear.
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Fermentation in Microorganisms
• Fermentation alone is able to sustain many types of
microorganisms.
• The lactic acid produced by microbes using fermentation is used
to produce:
– Cheese, sour cream, and yogurt dairy products
– Soy sauce, pickles, olives
– Sausage meat products
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• Yeast are a type of microscopic fungus that:
– Use a different type of fermentation
– Produce CO2 and ethyl alcohol instead of lactic acid
• This type of fermentation, called alcoholic fermentation, is used
to produce beer, wine, and breads
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INPUT
2 ADP
2 P
OUTPUT
2 ATP
2 CO2 released
Glycolysis
2 NAD 2 NADH
Glucose
2 NADH 2 NAD
2 Pyruvic
 2 H
2 Ethyl alcohol
acid
Figure 6.16a
Evolution Connection:
Life before and after Oxygen
• Glycolysis could be used by ancient bacteria to make ATP when
little oxygen was available, and before organelles evolved.
• Today, glycolysis:
– Occurs in almost all organisms
– Is a metabolic heirloom of the first stage in the breakdown of organic
molecules
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2.1
2.2
2.7
O2 present in
Earth’s atmosphere
Billions of years ago
0
First eukaryotic organisms
Atmospheric oxygen reaches 10% of modern levels
Atmospheric oxygen
first appears
3.5
Oldest prokaryotic
fossils
4.5
Origin of Earth
Figure 6.17
2.1
2.2
2.7
O2 present in
Earth’s atmosphere
Billions of years ago
0
First eukaryotic organisms
Atmospheric oxygen reaches 10% of modern levels
Atmospheric oxygen
first appears
3.5
Oldest prokaryotic
fossils
4.5
Origin of Earth
Figure 6.17a
Figure 6.17b
Oxidation
Glucose loses electrons
(and hydrogens)
C6H12O6
Glucose
 6
O2
Oxygen
6
CO2
Carbon
dioxide
 6
H 2O
Water
Reduction
Oxygen gains electrons (and hydrogens)
Figure 6.UN02
C6H12O6
Glucose
6
O2
Oxygen
6
CO2
Carbon
dioxide
6
H 2O
Water

ATP
Energy
Figure 6.UN01