Chapter 6
Cellular Respiration: Obtaining Energy from Food
Laua Coronado
Chap 6
Bio 10
Biology and :
Marathoners versuSocietys Sprinters
– Sprinters do not
usually compete at
short and long
distances.
– Natural differences in
the muscles of these
athletes favor
sprinting or longdistance running.
Laua Coronado
Chap 6
Bio 10
Muscle Fibers
–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
Laua Coronado
Chap 6
Bio 10
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.
Laua Coronado
Chap 6
Bio 10
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.
– Autotrophs are producers because ecosystems
depend upon them for food.
– Heterotrophs are consumers because they eat
plants or other animals.
Laua Coronado
Chap 6
Bio 10
Laua Coronado
Chap 6
Bio 10
Figure 6.1
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
Laua Coronado
Chap 6
Bio 10
Cellular Respiration
– 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
Laua Coronado
Chap 6
Bio 10
Cellular Respiration
– Animals perform only cellular respiration.
– Plants perform:
• Photosynthesis and
• Cellular respiration
Laua Coronado
Chap 6
Bio 10
Sunlight energy
enters ecosystem
C6H12O6
Photosynthesis
CO2
Glucose
Carbon dioxide
O2
Oxygen
H2O
Water
Cellular respiration
ATP drives cellular work
Heat energy exits ecosystem
Laua Coronado
Chap 6
Bio 10
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
Laua Coronado
Chap 6
Bio 10
CELLULAR RESPIRATION:
AEROBIC HARVEST OF FOOD ENERGY
–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.
Laua Coronado
Chap 6
Bio 10
CO2
O2
Breathing
Lungs
CO2
O2
Cellular
respiration
Laua Coronado
Chap 6
Bio 10
Muscle
cells
Figure 6.3
Oxidation
Glucose loses electrons
(and hydrogens)
C6H12O6
Glucose
 6
O2
6
Oxygen
CO2
 6
Carbon
dioxide
Reduction
Oxygen gains electrons (and hydrogens)
Laua Coronado
Chap 6
Bio 10
Figure 6.UN02
H2O
Water
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.
Laua Coronado
Chap 6
Bio 10
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.
Laua Coronado
Chap 6
Bio 10
Glycolysis
Citric
Acid
Cycle
ATP
ATP
Laua Coronado
Chap 6
Electron
Transport
ATP
Bio 10
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
Laua Coronado
Chap 6
Bio 10
1
O2
2
H2
Release
of heat
energy
H2O
Laua Coronado
Chap 6
Bio 10
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
Laua Coronado
Chap 6
Bio 10
e e Electrons from food
e e
NADH
NAD
2
H
Stepwise release
of energy used
to make
ATP
2 e
2 e
1
2
2 H
Hydrogen, electrons,
and oxygen combine
to produce water
Laua Coronado
Chap 6
O2
H2O
Bio 10
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
Laua Coronado
Chap 6
Bio 10
Mitochondrion
Cytoplasm
Cytoplasm
Animal cell
Plant cell
Cytoplasm
Mitochondrion
High-energy
electrons
carried
by NADH
Glycolysis
Glucose
High-energy
electrons carried
mainly by
NADH
Citric
Acid
Cycle
2
Pyruvic
acid
ATP
Electron
Transport
ATP
ATP
Laua Coronado
Chap 6
Bio 10
Figure 6.6
The Three Stages of Cellular Respiration
– 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.
• Three steps
– Uses two ATP molecules per glucose to split the sixcarbon glucose
– Makes four additional ATP directly when enzymes
transfer phosphate groups from fuel molecules to ADP
• Produces a net of two molecules of ATP per glucose
molecule.
Laua Coronado
Chap 6
Bio 10
INPUT
OUTPUT
2 ATP
2 ADP
Glucose
Key
Carbon atom
Phosphate
group
High-energy
electron
Energy investment phase
Laua Coronado
Chap 6
Bio 10
Figure 6.7-1
INPUT
OUTPUT
NADH
NAD
2 ATP
2 ADP
Glucose
Key
Carbon atom
Phosphate
group
High-energy
electron
NAD
NADH
Energy investment phase
Laua Coronado
Energy harvest phase
Chap 6
Bio 10
Figure 6.7-2
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
Laua Coronado
Energy harvest phase
Chap 6
Bio 10
Figure 6.7-3
Enzyme
P
ADP
ATP
P
P
Laua Coronado
Chap 6
Bio 10
Figure 6.8
Stage 2: The Citric Acid Cycle
– Completes the breakdown of sugar.
– In the citric acid cycle, pyruvic acid from
glycolysis is first “prepped.”
– 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
Laua Coronado
Chap 6
Bio 10
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
Laua Coronado
Coenzyme A
Chap 6
Bio 10
Acetic acid
attaches to
coenzyme A
Figure 6.9
Acetyl CoA
INPUT
OUTPUT
Citric
acid
Acetic
acid
2 CO2
ADP  P
ATP
Citric
Acid
Cycle
3 NAD
3 NADH
FAD
FADH2
Acceptor
molecule
Laua Coronado
Chap 6
Bio 10
Figure 6.10
Stage 3: 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.
Laua Coronado
Chap 6
Bio 10
Stage 3: Electron Transport
– 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
Laua Coronado
Chap 6
Bio 10
Space between
membranes
H
H
Electron
carrier
Protein
complex
Inner
mitochondrial
membrane
Electron
flow
Matrix
H
H
FADH2
FAD
H
H
H
H
H
H
NAD
H
H
H
1
2
NADH
H
H
H

O2  2 H
H2O
ADP 
H
H
H
ATP synthase
Electron transport chain
Laua Coronado
ATP
P
Chap 6
Bio 10
Figure 6.11
ETC Inhibitor
– 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
Laua Coronado
Chap 6
Bio 10
The Versatility of Cellular Respiration
– In addition to glucose, cellular respiration can
“burn”:
• Diverse types of carbohydrates
• Fats
• Proteins
Laua Coronado
Chap 6
Bio 10
Food
Polysaccharides
Fats
Proteins
Sugars
Fatty acids
Amino acids
Glycerol
Glycolysis
Citric
Acid
Cycle
Acetyl
CoA
Electron
Transport
ATP
Laua Coronado
Chap 6
Bio 10
Figure 6.12
Cytoplasm
Mitochondrion
NADH
2
2
Glycolysis
2
Pyruvic
acid
NADH
6
NADH
2
FADH2
2
Acetyl
CoA
Citric
Acid
Cycle
Electron
Transport
2
ATP
2
ATP
About
34 ATP
by direct
synthesis
by direct
synthesis
Glucose
Laua Coronado
Chap 6
Maximum
per
glucose:
by ATP
synthase
Bio 10
Figure 6.13
About
38 ATP
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.
Laua Coronado
Chap 6
Bio 10
Laua Coronado
Chap 6
Bio 10
FERMENTATION: ANAEROBIC HARVEST
OF FOOD ENERGY
– 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 byproduct.
Laua Coronado
Chap 6
Bio 10
INPUT
2 ADP
2 P
OUTPUT
2 ATP
Glycolysis
2 NAD
2 NADH
Glucose
Laua Coronado
Chap 6
Bio 10

2 NADH 2 NAD
2 Pyruvic
 2 H
acid
Figure 6.14
2 Lactic acid
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.
Laua Coronado
Chap 6
Bio 10
Battery
Battery
Force
measured
Force
measured
Frog muscle
stimulated by
electric current
Solution allows
diffusion of lactic acid;
muscle can work for
twice as long
Solution prevents
diffusion of lactic acid
Laua Coronado
Chap 6
Bio 10
Figure 6.15
The Process of Science:
Does Lactic Acid Buildup Cause Muscle Burn?
– 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.
Laua Coronado
Chap 6
Bio 10
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
Laua Coronado
Chap 6
Bio 10
Fermentation in Microorganisms
– 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
• Breads
Laua Coronado
Chap 6
Bio 10
INPUT
2 ADP
2 P
OUTPUT
2 ATP
2 CO2 released
Glycolysis
2 NAD
Glucose
2 NADH
2 NADH
2 NAD
2 Pyruvic

2 H
acid
Laua Coronado
Chap 6
Bio 10
2 Ethyl alcohol
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
Laua Coronado
Chap 6
Bio 10
Billions of years ago
2.1
2.2
2.7
O2 present in
Earth’s atmosphere
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
Laua Coronado
Chap 6
Bio 10
Figure 6.17
Heat
C6H12O6
Sunlight
O2
ATP
Cellular
respiration
Photosynthesis
H2O
CO2
Laua Coronado
Chap 6
Bio 10
Figure 6.UN06
C6H12O6
6
O2
6
Laua Coronado
Chap 6
CO2
Bio 10
6
H2 O
 Approx. 38
Figure 6.UN07
ATP
Oxidation
Glucose loses electrons
(and hydrogens)
CO2
C6H12O6
Electrons
(and hydrogens)
ATP
H2O
O2
Reduction
Oxygen gains
electrons (and
hydrogens)
Laua Coronado
Chap 6
Bio 10
Figure 6.UN08
Mitochondrion
O2
NADH
2
2
NADH
Glycolysis
NADH
2
FADH2
2
Acetyl
CoA
2
Pyruvic
acid
Glucose
6
Citric
Acid
Cycle
4 CO2
2 CO2
2
ATP
by direct
synthesis
Electron
Transport
by direct
synthesis
2
ATP
H2O
About
34 ATP
by ATP
synthase
About
38 ATP
Laua Coronado
Chap 6
Bio 10
Figure 6.UN09