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Chapter 9: Cellular Respiration
How Cells Make ATP:
Energy-Releasing Pathways
Summary:
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Cellular respiration - the process by which
your cells transfer the energy in organic
compounds to ATP.
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The byproduct of this reaction is water and carbon
dioxide.
It occurs in the cells mitochondria, which are the
energy producers for the cell.
Summary:
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Each cell converts the energy in the chemical
bonds of nutrients to chemical energy stored
in ATP
May be aerobic or anaerobic
Most cells use aerobic respiration
3 pathways that are exergonic and release
energy:
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Aerobic respiration
Anaerobic respiration
Fermentation
Aerobic Respiration
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Most eukaryotes and prokaryotes
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To obtain energy from glucose
Requires oxygen
Nutrients are catabolized to CO2 and H2O
Glucose + Oxygen
Carbon Dioxide + Water
+ Energy (in bonds of ATP)
Aerobic Respiration
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A redox process
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Glucose is oxidized to form Carbon Dioxide
Oxygen is reduced, forming water
The electrons produced are used to form
ATP
Aerobic Respiration
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3 stages:
1.
2.
3.
Glycolysis
Citric Acid (Krebs) Cycle
Electron Transport Chain and Chemiosmosis
Aerobic Respiration
*In eukaryotes, glycolysis occurs in cytosol and
remaining 2 steps occur in mitochondria.
* In bacteria, all stages occur in cytosol working
with plasma membrane.
Mitochondrion Structure
Glycolysis
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Occurs in cytosol
Glucose converted to two 3-carbon
molecules of pyruvic acid
ATP and NADH are formed
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NADH - temporarily stores large amounts of free
energy
Energy from NADH ultimately participates in
reactions that form ATP
Net production of 2 ATP
Animation of Glycolysis
Advantages of Glycolysis
The process of glycolysis is so fast that cells can
produce thousands of ATP molecules in a few
milliseconds.
Glycolysis does not require oxygen.
Citric Acid Cycle (Krebs Cycle)
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Pyruvic Acid from Glycolysis moves into
mitochondria.
Pyruvic acid breaks apart
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1 molecule of CO2 is produced
2 other Carbon atoms form acetyl CoA
Acetyl CoA combines with 4 carbon
molecules to produce citric acid.
Citric Acid Cycle (Krebs Cycle)
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Citric Acid is broken down
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CO2 released
Electrons transferred to energy carriers.
Carbon Dioxide is a waste product
ATP, NADH and FADH2 are produced
2 ATP are produced/glucose
Electron Transport Chain and
Chemiosmosis
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Electrons from Krebs cycle are passed to
NADH and FADH2 in Electron Transport
Chain
Enzymes present in mitochondrial membrane
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As NADH and FADH2 pass along enzymes, they
give up electrons (energy) = chemiosmosis
H+ ions are transported across membrane and
come in contact with ATP synthase
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ADP + Pi = ATP
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End of chain – electrons combined with
oxygen and hydrogen to form water
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Via chemiosmosis, 34 ATP produced.
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ATP synthesis continues until ADP stores are
depleted
Equation
C6H12O6 + 6O2 -->6 CO2 + 6H2O + 38 ATP
Aerobic Respiration – End Results
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One glucose gives maximum of 36-38 ATP’s
Glycolysis produces 2 ATP molecules
2 ATP molecules are produced in the citric
acid cycle
Remainder of ATP is produced in the electron
transport system (32 or 34)
Efficiency is about 40%; remaining energy is
disseminated as heat
Other nutrients (besides glucose) provide
energy
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More energy is gained from burning fats than
glucose
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Lipids contain 9 kcal/gram
Lipids are broken down and glycerol enters
glycolysis
Fatty acids are converted to acetyl CoA and enter
the citric acid cycle
Proteins are broken down to amino acids
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Proteins contain 4 kcal/gram
Anaerobic Respiration and Fermentation
do not Require Oxygen
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Anaerobic Respiration
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Various inorganic substances serve as the final
electron acceptor
Yield is only the 2 ATP molecules from glycolysis
Types of Fermentation
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Alcohol
Lactate
Alcoholic Fermentation
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Alcoholoic fermentation
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Alcoholic fermentation produces ethanol
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Pyruvate is converted to ethanol
Ethanol is a potentially toxic waste product
Yeast carry out alcoholic fermentation when
oxygen deprived
Pyruvic acid + NADH -> alcohol + CO2 + NAD+
Lactate Fermentation
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Bacteria and some fungi carry out lactate
fermentation
Strenuous exercise in mammals results in
lactate fermentation as well
Yields only the 2 ATP molecules from
glycolysis
Pyruvic acid + NADH -> lactic acid + NAD+
Fermentation
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