chapter 9 cellular respiration: harvesting chemical energy
TRANSCRIPT
Chapter 9
Cellular Respiration: Harvesting Chemical Energy
Energy flows into an ecosystem as sunlight and leaves as heat
Photosynthesis generates O2 and organic molecules, which are used in cellular respiration
Cellular respiration: Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work
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Fig. 9-2
Lightenergy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2 + H2O
Cellular respirationin mitochondria
Organicmolecules+ O2
ATP powers most cellular work
Heatenergy
ATP
Catabolic Pathways and Production of ATP
Fermentation is a partial degradation of sugars that occurs without O2 (no oxygen)
Aerobic respiration consumes organic molecules and O2 and yields ATP (requires O2)
Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 (does not require oxygen)
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Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)
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Redox Reactions: Oxidation and Reduction
The transfer of electrons during chemical reactions releases energy stored in organic molecules
This released energy is ultimately used to synthesize ATP
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The Principle of Redox
In oxidation, a substance loses electrons, or is oxidized- The electron donor is called the reducing agent
In reduction, a substance gains electrons, or is reduced - The electron receptor is called the oxidizing agent
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becomes oxidized(loses electron)
becomes reduced(gains electron)
becomes oxidized
becomes reduced
The Stages of Cellular Respiration: A Preview
Cellular respiration has three stages: Glycolysis (breaks down glucose into two
molecules of pyruvate) The citric acid cycle (completes the breakdown of
glucose) Oxidative phosphorylation (accounts for most of
the ATP synthesis)
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Fig. 9-6-3
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Oxidativephosphorylation
ATP
Citricacidcycle
Oxidativephosphorylation:electron transport
andchemiosmosis
The process that generates most of the ATP is called oxidative phosphorylation because it is powered by redox reactions
Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration
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Glycolysis
Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate
Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase (input 2 ATP) Energy payoff phase (produces 4 ATP)
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Fig. 9-8
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
2 Pyruvate + 2 H2O
2 Pyruvate + 2 H2OGlucoseNet
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+
The citric acid cycle (Kreb Cycle)
In the presence of O2, pyruvate enters the mitochondrion (matrix)
Pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis
Generates 1 ATP, 3 NADH, and 1 FADH2 per turn
The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain
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Animation: MitochondriaAnimation: Mitochondria
Fig. 9-10
CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Pyruvate
Transport protein
CO2Coenzyme A
Acetyl CoA
Fig. 9-11
Pyruvate
NAD+
NADH
+ H+Acetyl CoA
CO2
CoA
CoA
CoA
Citricacidcycle
FADH2
FAD
CO22
3
3 NAD+
+ 3 H+
ADP + P i
ATP
NADH
The Pathway of Electron Transport
The electron transport chain is in the cristae of the mitochondrion
NADH and FADH2 donate electrons to the electron transport chain
Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O
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Electrons are passed through a number of proteins
The electron transport chain generates no ATP
The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts
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Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
H+ then moves back across the membrane, passing through channels in ATP synthase
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VCAC: Cellular Processes: Electron Transport Chain: First LookVCAC: Cellular Processes: Electron Transport Chain: First Look
VCAC: Cellular Processes: ATP Synthase: The MovieTransport VCAC: Cellular Processes: ATP Synthase: The MovieTransport
Fig. 9-14INTERMEMBRANE SPACE
Rotor
H+
Stator
Internalrod
Cata-lyticknob
ADP+P ATP
i
MITOCHONDRIAL MATRIX
ATP Production by Cellular Respiration
Glycolysis- 2 ATP Citric Acid cycle- 2 ATP ATP Synthase- 32 or 34 Total- 38 ATP
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Fermentation and anaerobic respiration
• Most cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP
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Types of Fermentation
Two common types are alcohol fermentation and lactic acid fermentation
In alcohol fermentation pyruvate is converted to ethanol Yeast - in brewing, winemaking, and baking
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In lactic acid fermentation, lactate is the end product
Fungi and bacteria - make cheese and yogurt Human muscle cells use lactic acid
fermentation to generate ATP when O2 is scarce
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Fig. 9-19Glucose
Glycolysis
Pyruvate
CYTOSOL
No O2 present:Fermentation
O2 present:
Aerobic cellular respiration
MITOCHONDRION
Acetyl CoAEthanolor
lactateCitricacidcycle