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7.1 Cellular Respiration
Essentials of
Biology
•
•
Produces ATP molecules
Requires O2; CO2 a waste product
•
Sylvia S. Mader
Chapter 7
Cellular Respiration—Energy
for Cells
Lecture Outline
The reason we breath!
•
Essentially the reverse of photosynthesis
•
BioFlix Cellular Respiration:
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Figure 7.1 Cellular Respiration
Figure 7.2 The four phases of complete glucose breakdown
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Cytoplasm
NADH and
FADH2
Glycolysis
glucose
2
1.
2.
e–
pyruvate
ATP
Preparatory reaction
Citric acid
cycle
2
ATP
Electron
transport
chain
34
ATP
Glycolysis
3. Citric acid cycle
Preparatory reaction 4. Electron transport chain
Key Terms
• Oxidation = removal of hydrogen atoms
 Hydrogens removed from glucose, C6H12O6
 Produces CO2 as a waste product
• Reduction = addition of hydrogen atoms
 Oxygen accepts hydrogens
 Produces H2O as a waste product
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Figure 7.3
Glycolysis
• Energyinvestment steps
 2 ATP transfer
phosphates to
glucose
 Activates them
for next steps
1. Glycolysis
•
•
Takes place in the cytoplasm
Glucose (6 carbons) broken down into two molecules of
pyruvate (3 carbon)
Divided into…
•
–
–
Figure 7.3 Glycolysis
- Glucose broken down gradually in steps
- Allows energy to be captured and used to make ATP
Energy-investment steps
Energy-harvesting steps
• Energy-harvestingsteps
 Substrate-level ATP
synthesis produces 4
ATP
 Net gain of 2 ATP
 2 NADH made
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Figure 7.4
Figure 7.3 Glycolysis
Glycolysis Totals
• Next step depends on
oxygen availability
 With oxygen…
• pyruvate enters mitochondria
 Without oxygen…
7.3 Inside the Mitochondria
Cytoplasm
location of glycolysis
• Other 3 phases take
place inside the
mitochondria
outer membrane
• pyruvate undergoes reduction
matrix
cristae
Matrix
location of the prep
reaction and the citric
acid cycle
NADH and
FADH2
e–
Glycolysis
Preparatory reaction
Citric acid
cycle
inner membrane
forms cristae
Intermembrane
space
Electron
transport
chain
Cristae
location of the electron
transport chain
2
ATP
matrix
2
ATP
Figure 7.6
34
ATP
Figure 7.5 Mitochondrion
structure and function
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2. Preparatory Reaction
•
Occurs in mitochondrial
matrix
Only occurs if O2 present
Occurs twice per glucose
molecule
Produces
•
•
•


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CO2 (waste product)
NADH
•
•
•

H—Carrier
Goes to ETC
3 ATP per NADH
Acetyl CoA
•
•
2-Carbon sugar
Enters citric acid cycle or
converted to fatty acids
Fig. 7.6
3. Citric Acid Cycle
Citric Acid Cycle
-
Acetyl CoA    2 CO2+ 2 ATP + 6 NADH + 2 FADH2

Step by step breakdown of acetyl CoA to CO2

8 steps in all, each catalyzed by a different enzyme
- Occurs in the matrix of mitochondria
- Aerobic: will only occur if oxygen is available
Citric acid cycle
4. Electron Transport Chain
4.
Electron Transport Chain



Series of carrier proteins on inner membrane
Electrons passed from one protein carrier to another
NADH and FADH2 deliver electrons
•
•

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Hydrogen atoms attached consist of e- and H+
Carriers accept only e- not H +
O2 is the final electron acceptor
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4. Electron Transport Chain
• High-energy electrons
enter, low-energy
electrons leave
• As pair of electrons
passed from one
carrier to the next,
energy is released
• Will be captured as
ATP
• Final electron acceptor
is oxygen – forms
water
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Figure 7.7
ATP yield per glucose molecule
4. Electron Transport Chain
• Electrons pass from carrier to carrier of the E.T.C.
 What is the final electron acceptor?
• Energy used to pump H + from matrix into intermembrane space –
creates H+ gradient
• H+ diffuse back into matrix through ATP synthase
 Activates ATP synthase to make _____???________
Figure 7.8
• Maximum of 38 ATP
made
• Some cells make only 36
ATPs or less
• 40% of available energy in
a glucose molecule
captured as ATP
 Rest is lost as…
____????_____
Figure 7.9
Electron Transport Chain
Alternate Metabolic Pathways
ATP Synthesis
Alternate Metabolic Pathways
• Cells use other energy
sources
• Fatty acids have longer
carbon chains – yields more
ATP
• Intermediates can also be
used to make other
products
• Extra food made into fat for
storage 
Figure 7.10
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7.4 Fermentation
• O2 is required for the complete breakdown of glucose
• Fermentation:
 anaerobic breakdown of glucose
 Generates only 2 ATP 
• Animal & Bacteria: Lactic Acid Fermentation
 Pyruvate reduced to lactate (lactic acid)
• Lactate is toxic to cells—why make it?
 Brief burst of energy for muscle cells
 Recovery from oxygen deficit complete when enough oxygen is
present to completely break down glucose
Lactic Acid Fermentation
 Pyruvate reduced to lactate
 Brief burst of energy for muscle
cells
• Only produces 2 ATP
 Recovery from O2 deficit when
enough O2 available to
completely break down glucose
• Lactate converted back to pyruvate
or glucose
• Lactate is toxic to cells—why
make it
• Lactate converted back to pyruvate or glucose
Figure 7.11
Fermentation
Lactic Acid Fermentation (animals & bacteria)
Regenerates NAD+ to keep glycolysis going under anaerobic conditions
Similar to Fig. 7.11
Microorganisms &
Fermentation
• Bacteria
 Fermentation produces
Lactate or other acids
 Yoghurt
• Yeast
 Fermentation produces
alcohol & CO2
• CO2 makes bread rise
• Ethanol made in wine and
beer
Alcoholic Fermentation (yeast)
Regenerates NAD+ to keep glycolysis going under anaerobic conditions
Similar to Fig. 7.11
Oxygen Free Radical Theory of Aging
• Oxygen is slowly killing us!
• Raj Sohal’s (Southern Methodist University)
– Has tripled the life span of house flies if he restricts
there movement and hence the amount of oxygen
they consume.
– Used Gene therapy to double lifespan of house fly!
– Inserted genes that encode enzymes that deactivate
free radicals
• SOD (superoxide dismutase) and Catalase
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Superoxide radical, O2 , formation
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Oxygen Free Radical Theory of Aging
O2 generated constantly as part of normal aerobic life
O2 formed in mitochondria when O2 is reduced along the electron transport chain
• SOD and catalase levels increase when humans
exercise, thus protecting us from the extra free
radicals produced as a consequence of increased
oxygen consumption.
• House flies do not have the genes to produce
SOD and catalase consequences?
Oxygen Free Radical Theory of Aging
1. Vitamin C (water-soluble) and Vitamin E (fatsoluble) are vitamins that deactivate free
radicals.
2. Why might it be beneficial to take both of them,
rather than just one or the other?
Glucose Cross-linking with Proteins
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Diabetics
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Higher than normal blood levels of glucose.
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Causes diabetics to age ~one-third faster
Glucose is Slowly Killing Us!! 
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Glucose reacts with proteins to form cross-links
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Results in irreversible damage to sensitive
proteins (e.g. collagen, hemoglobin, receptors,
cell structures)
Glucose Cross-linking with Proteins
•
Cross-linking makes
proteins less flexible
–
makes body parts less
flexible and stiffer
–
major cause of aging in
many tissues:
•
Glucose Cross-link
skin, bones, lungs,
eyes, joints, and
blood vessels.
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