Transcript Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration:
Harvesting Chemical
Energy
Chapter 9
Biology – Campbell • Reece
Harvesting Energy

Release stored energy by breaking down
complex molecules in catabolic
processes
– Fermentation – break down sugars
without oxygen
– Aerobic (Cellular) Respiration – break
down of organic compounds
(carbohydrates, fats, and proteins) with
oxygen
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C6H12O6 + 6O2 → 6CO2 + 6H2O + energy
Redox Reactions
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A.K.A. oxidation-reduction reactions
Oxidation – the loss of electrons
Reduction – the addition of electrons
The Stages of Cellular
Respiration
1.
Glycolysis
– Occurs in the cytosol
2.
The citric acid cycle (Krebs Cycle)
– Occurs in the mitochondrial matrix
3.
Oxidative phosphorylation: electron
transport and chemiosmosis
– Occurs on the inner membrane of the
mitochondrion
Substrate-level
Phosphorylation
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ATP synthesis in glycolysis and the
citric acid cycle occurs when an
enzyme transfers a phosphate from a
substrate molecule to ADP
Glycolysis
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“sugar splitting”
Glucose is split into two three-carbon
sugars, which are converted to
pyruvate
Two phases:
– Energy investment – 2 ATP are used
– Energy payoff – 4 ATP produced + 2
NADH
Glycolysis
Glycolysis Overview
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Inputs:
– Glucose
– 2 ATP
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Outputs:
– Pyruvate
– 4 ATP
– 2 NADH
After Glycolysis
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If oxygen is present, the pyruvate
enters the mitochondrion
In prokaryotic cells, the next step
occurs in the cytosol
If oxygen is not present…
Citric Acid Cycle
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A.K.A. Krebs Cycle
Pyruvate is converted to acetyl
coenzyme A (acetyl CoA)
– CO2 is released
– NADH is produced
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The acetyl CoA enters the citric acid
cycle
The cycle runs twice for each glucose
molecule
Citric Acid Cycle Overview
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Inputs:
– 2 pyruvate/
acetyl CoA
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Outputs:
–6
–8
–2
–2
CO2
NADH
FADH2
ATP
Electron Transport Chain
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A collection of molecules imbedded in the
inner membrane of the mitochondrion
(bound in multiprotein complexes I through
IV)
Electrons are transferred from the NADH to
the first molecule in the chain
The electrons are passed from complex I to
complex II and then continue down the
chain
Electron Transport Chain
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At the end of the chain, the electrons are
passed to oxygen which then picks up a pair of
hydrogen ions, forming water
FADH2 adds electrons to the chain starting at
complex II
Complexes I, III, and IV pump H+ from the
mitochondrial matrix into the intermembrane
space resulting in a higher concentration on
one side
Electron Transport Chain
Chemiosmosis
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The energy released by the electron
transport chain is used to power the process
of ATP synthesis (energy coupling)
Chemiosmosis uses energy stored in the
form of a hydrogen ion gradient across a
membrane to synthesize ATP
ATP synthase is an enzyme embedded in
the inner membrane of the mitochondria
that makes ATP from ADP and inorganic
phosphate
ATP Synthase and the ETC
ATP Synthase
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When the rotor of the ATP synthase
turns in one direction, ATP is
hydrolyzed
When it turns the other direction, ATP
is synthesized
The H+ ions pass through the ATP
synthase providing energy to power
ATP synthesis
Electron Transport Chain
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Inputs:
– 10 NADH
– 2 FADH2
– 6 O2
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Outputs:
– ~32 ATP
– 6 H2O
How much ATP?
Anaerobic Respiration
and Fermentation
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Generate ATP without oxygen
Certain prokaryotes that live in environments
without oxygen use anaerobic respiration
(some use a sulfate ion as the final electron
acceptor)
Fermentation lacks any electron transport
chain
– Consists of glycolysis plus reactions that
regenerate NAD+
Types of Fermentation
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Alcohol fermentation – pyruvate is
converted to ethanol, producing 2 ATP and
2 CO2
– Used in brewing, winemaking, baking
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Lactic acid fermentation – pyruvate is
converted to lactic acid, producing 2 ATP
– Used to make cheese and yogurt
– Human muscle cells use LAF when oxygen is
scarce
Types of Fermentation