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How Cells make ATP:How Cells make ATP:Energy-Releasing PathwaysEnergy-Releasing Pathways
Chapter 8
Learning Objective 1Learning Objective 1
• In aerobic respiration, which reactant is oxidized and which is reduced?
Aerobic RespirationAerobic Respiration
• A catabolic process• fuel (glucose) broken down to carbon
dioxide and water
• Redox reactions • transfer electrons from glucose (oxidized)• to oxygen (reduced)
• Energy released • produces 36 to 38 ATP per glucose
KEY CONCEPTSKEY CONCEPTS
• Aerobic respiration is an exergonic redox process in which glucose becomes oxidized, oxygen becomes reduced, and energy is captured to make ATP
Learning Objective 2Learning Objective 2
• What are the four stages of aerobic respiration?
4 Stages of 4 Stages of Aerobic Respiration Aerobic Respiration
1. Glycolysis
2. Formation of acetyl CoA
3. Citric acid cycle
4. Electron transport chain and chemiosmosis
GlycolysisGlycolysis
• 1 molecule of glucose degraded• to 2 molecules pyruvate
• 2 ATP molecules (net) produced• by substrate-level phosphorylation
• 4 hydrogen atoms removed• to produce 2 NADH
GlycolysisGlycolysis
Fig. 8-3, p. 175
32 ATP
Glycolysis
Glucose
Pyruvate
2 ATP
Formationof acetyl
coenzyme A
Citric acidcycle
2 ATP
Electron transportand
chemiosmosis
Fig. 8-3, p. 175
GLYCOLYSIS
Energy investment phase and splitting of glucose
Two ATPs invested per glucose
Glucose
3steps
2 ATP
2 ADP
Fructose-1,6-bisphosphate
PP
PP
Glyceraldehydephosphate
(G3P)
Glyceraldehydephosphate
(G3P)
Fig. 8-3, p. 175
Energy capture phaseFour ATPs and two NADH
produced per glucose
P P
(G3P) (G3P)
NAD+ NAD+
NADH
2 ADP
2 ATP
Pyruvate
5steps
NADH
2 ADP
2 ATP
Net yield per glucose:Two ATPs and two NADH
Pyruvate
Formation of Acetyl CoAFormation of Acetyl CoA
• 1 pyruvate molecule• loses 1 molecule of carbon dioxide
• Acetyl group + coenzyme A• produce acetyl CoA
• 1 NADH produced per pyruvate
Formation of Acetyl CoAFormation of Acetyl CoA
Fig. 8-5, p. 178
Electron transportand
chemiosmosis
Glycolysis
Glucose
Pyruvate
2 ATP
Formationof acetyl
coenzyme A
2 ATP 32 ATP
Citric acidcycle
Fig. 8-5, p. 178
NAD+
Coenzyme A
Acetyl coenzyme A
Pyruvate
Carbondioxide
CO2
NADH
Citric Acid CycleCitric Acid Cycle
• 1 acetyl CoA enters cycle• combines with 4-C oxaloacetate• forms 6-C citrate
• 2 C enter as acetyl CoA• 2 leave as CO2
• 1 acetyl CoA • transfers H atoms to 3 NAD+
, 1 FAD• 1 ATP produced
Citric Acid CycleCitric Acid Cycle
Fig. 8-6, p. 179
Electron transportand
chemiosmosis
Glycolysis
Glucose
Pyruvate
2 ATP
Formationof acetyl
coenzyme A
2 ATP 32 ATP
Citric acidcycle
Fig. 8-6, p. 179
Oxaloacetate
NADH
NAD+
H2O
FADH2
FAD
GTPGDP
ADPATP
C I T R I CA C I D
C Y C L E
4-carbon compound
Acetyl coenzyme A Coenzyme A
Citrate
NAD+
NADH
CO2
CO2
NADH
5-carbon compound
Electron Transport Chain Electron Transport Chain
• H atoms (or electrons) transfer• from one electron acceptor to another• in mitochondrial inner membrane
• Electrons reduce molecular oxygen• forming water
Electron Transport ChainElectron Transport Chain
Fig. 8-8, p. 181
Cytosol
Outer mitochondrial membrane
Intermembrane space
Complex I: NADH–ubiquinone
oxidoreductaseComplex II: Succinate– ubiquinone reductase
Complex III: Ubiquinone– cytochrome c oxidoreductase
Complex IV: Cytochrome c oxidaseInner
mitochondrial membrane
Matrix of mitochondrion FADH2
FAD 2 H+
H2O
NAD+ 1/2 O2
NADH
Oxidative Phosphorylation Oxidative Phosphorylation
• Redox reactions in ETC are coupled to ATP synthesis through chemiosmosis
KEY CONCEPTSKEY CONCEPTS
• Aerobic respiration consists of four stages: glycolysis, formation of acetyl coenzyme A, the citric acid cycle, and the electron transport chain and chemiosmosis
Learning Objective 3Learning Objective 3
• Where in a eukaryotic cell does each stage of aerobic respiration take place?
Aerobic RespirationAerobic Respiration
• Glycolysis occurs in the cytosol
• All other stages in the mitochondria
Fig. 8-2, p. 173
1 2 3 4Glycolysis Formation of
acetyl coenzyme A
Citric acid cycle
Electron transport and chemiosmosis
Glucose
Mitochondrion
Acetyl coenzyme
A
Citric acid cycle
Electron transport and chemiosmosis
Pyruvate
2 ATP 2 ATP 32 ATP
Learning Objective 4Learning Objective 4
• Add up the energy captured (as ATP, NADH, and FADH2) in each stage of aerobic respiration
Energy CaptureEnergy Capture
• Glycolysis• 1 glucose: 2 NADH, 2 ATP (net)
• Conversion of 2 pyruvates to acetyl CoA• 2 NADH
• Citric acid cycle• 2 acetyl CoA: 6 NADH, 2 FADH2, 2 ATP
• Total: 4 ATP, 10 NADH, 2 FADH2
Energy TransferEnergy Transfer
• Electron transport chain (ETC)• 10 NADH and 2 FADH2 produce 32 to 34
ATP by chemiosmosis
• 1 glucose molecule yields 36 to 38 ATP
Energy from GlucoseEnergy from Glucose
Fig. 8-11, p. 185
Substrate-level phosphorylation Glycolysis
Oxidative phosphorylation
Pyruvate
Acetyl coenzyme
A
Citric acid cycle
Total ATP from substrate-level
phosphorylation
Total ATP from oxidative
phosphorylation
Glucose
Learning Objective 5Learning Objective 5
• Define chemiosmosis
• How is a gradient of protons established across the inner mitochondrial membrane?
ChemiosmosisChemiosmosis
• Energy of electrons in ETC• pumps H+ across inner mitochondrial
membrane• into intermembrane space
• Protons (H+) accumulate in intermembrane space• lowering pH
Proton GradientProton Gradient
Fig. 8-9, p. 183
Outer mitochondrial membrane
Inner mitochondrial membrane
Matrix — higher pH
Intermembrane space — low pH
Cytosol
Learning Objective 6Learning Objective 6
• How does the proton gradient drive ATP synthesis in chemiosmosis?
ATP SynthaseATP Synthase
• Enzyme ATP synthase• forms channels through inner mitochondrial
membrane
• Diffusion of protons through channels provides energy to synthesize ATP
ETC and ChemiosmosisETC and Chemiosmosis
Fig. 8-10a, p. 184
Intermembranespace
Cytosol
Outer mitochondrial
membrane
Matrix ofmitochondrion
Innermitochondrial
membrane
Complex I
NADH
NAD+
FADH2
ComplexII
ComplexIII
ComplexIV
12
ADP PiATP
Complex V:ATP
synthase
Fig. 8-10b, p. 184
Projections of ATP synthase
250 nm
(b) This TEM shows hundreds of projections of ATP synthase complexes along the surface of the inner mitochondrial membrane.
Learning Objective 7Learning Objective 7
• How do the products of protein and lipid catabolism enter the same metabolic pathway that oxidizes glucose?
Amino AcidsAmino Acids
• Undergo deamination
• Carbon skeletons converted• to intermediates of aerobic respiration
LipidsLipids
• Glycerol and fatty acids • both oxidized as fuel
• Fatty acids• converted to acetyl CoA by β-oxidation
Catabolic PathwaysCatabolic Pathways
Fig. 8-12, p. 186
PROTEINS CARBOHYDRATES FATS
Amino acids
Glucose
Glycolysis Fatty acids
Glycerol
G3P
PyruvateCO2
Acetyl coenzyme
A
Citric acid cycle
Electron transport and chemiosmosis
End products: NH3 H2O CO2
Citric acid cycle
CO2
CARBOHYDRATES
Glucose
Glycolysis
G3P
Pyruvate
Stepped Art
Fig. 8-12, p. 186
PROTEINS
Amino acids
Fatty acids
FATS
Glycerol
CO2
Acetyl coenzyme
A
End products: NH3
Electrontransport and chemiosmosis
H2O
KEY CONCEPTSKEY CONCEPTS
• Nutrients other than glucose, including many carbohydrates, lipids, and amino acids, can be oxidized by aerobic respiration
Learning Objective 8Learning Objective 8
• Compare the mechanism of ATP formation, final electron acceptor, and end products of anaerobic respiration and fermentation
Anaerobic RespirationAnaerobic Respiration
• Electrons transferred• from fuel molecules to ETC • coupled to ATP synthesis (chemiosmosis)
• Final electron acceptor• inorganic substance• nitrate or sulfate (not molecular oxygen)
KEY CONCEPTSKEY CONCEPTS
• In anaerobic respiration carried out by some bacteria, ATP is formed during a redox process in which glucose becomes oxidized and an inorganic substance becomes reduced
FermentationFermentation
• Anaerobic process• no ETC
• Net energy gain only 2 ATP per glucose• produced by substrate-level
phosphorylation during glycolysis
• NAD+
• produced by transferring H from NADH to organic compound from nutrient
FermentationFermentation
• Alcohol fermentation • in yeast cells• waste products: ethyl alcohol, CO2
• Lactate (lactic acid) fermentation• some fungi, prokaryotes, animal cells• H atoms added to pyruvate• waste product: lactate
KEY CONCEPTSKEY CONCEPTS
• Fermentation is an inefficient anaerobic redox process in which glucose becomes oxidized and an organic substance becomes reduced
• Some fungi and bacteria, as well as muscle cells under conditions of low oxygen, obtain low yields of ATP through fermentation
FermentationFermentation
Fig. 8-13, p. 187
Fig. 8-13a, p. 187
25 μm
Fig. 8-13b, p. 187
Glycolysis
Glucose
2 NAD+ 2 NADH
2 ATP
2 Pyruvate
CO2
2 Ethyl alcohol
(b) Alcohol fermentation
Fig. 8-13c, p. 187
Glycolysis
Glucose
2 NAD+ 2 NADH
2 ATP
2 Pyruvate
2 Lactate
(c) Lactate fermentation
Summary Reaction Summary Reaction
• Complete oxidation of glucose
C6H12O6 + 6 O2 + 6 H2O →
6 CO2 + 12 H2O + energy (36 to 38 ATP)
Summary ReactionSummary Reaction
• Glycolysis
C6H12O6 + 2 ATP + 2 ADP + 2 Pi + 2 NAD+
→ 2 pyruvate + 4 ATP + 2 NADH + H2O
Glycolysis in DetailGlycolysis in Detail
Fig. 8-4a, p. 176
Energy investment phase and splitting of glucose
Two ATPs invested per glucose
GlucoseGlycolysis begins with preparation reaction in which glucose receives phosphate group from ATP molecule. ATP serves as source of both phosphate and energy needed to attach phosphate to glucose molecule. (Once ATP is spent, it becomes ADP and joins ADPpool of cell until turned into ATP again.) Phosphorylated glucose is known as glucose-6-phosphate. (Note phosphate attached to its carbon atom 6.) Phosphorylation of glucose makes it more chemically reactive.
ATP
ADP
Glucose-6-phosphate
Hexokinase
Phosphoglucoisomerase
1
Fig. 8-4a, p. 176
Glucose-6-phosphate undergoes another preparation reaction, rearrangement of its hydrogen and oxygen atoms. In this reaction glucose-6-phosphate is converted to its isomer, fructose-6-phosphate.
Next, another ATP donates phosphate to molecule, forming fructose-1,6-bisphosphate. So far, two ATP molecules have been invested in process without any being produced. Phosphate groups are now bound at carbons 1 and 6, and molecule is ready to be split.
Fructose-1,6-bisphosphate is then split into two 3-carbon sugars, glyceraldehyde-3- phosphate (G3P) and dihydroxyacetone phosphate.
Dihydroxyacetone phosphate is enzymatically converted to its isomer, glyceraldehyde-3- phosphate, for further metabolism in glycolysis.
Fructose-6-phosphate
PhosphofructokinaseATP
ADP
Fructose-1,6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate (G3P)
2
3
4
5
Fig. 8-4b, p. 177
Energy capture phaseFour ATPs and two NADH produced per
glucose
Two glyceraldehyde-3-phosphate (G3P)from bottom of previous page
2 NAD+
2 NADH
Glyceraldehyde-3-phosphate dehydrogenase
Phosphoglycerokinase
Two 1,3-bisphosphoglycerate
2 ADP
2 ATP
Each glyceraldehyde-3-phosphate undergoes dehydrogenationwith NAD+ as hydrogen acceptor. Productof this very exergonic reaction is phosphoglycerate,which reacts with inorganic phosphate present incytosol to yield 1,3-bisphosphoglycerate.
One of phosphates of 1,3-bisphosphoglycerate reactswith ADP to form ATP. This transfer of phosphate fromphosphorylated intermediate to ATP is referred to assubstrate-level phosphorylation.
Two 3-phosphoglycerate
Phosphoglyceromutase
6
7
Fig. 8-4b, p. 177
Two 2-phosphoglycerate
Enolase
Pyruvate kinase
Two pyruvate
2 H2O
Two phosphoenolpyruvate2 ADP
2 ATP
3-phosphoglycerate is rearranged to 2-phosphoglycerateby enzymatic shift of position of phosphate group.This is a preparation reaction.
Next, molecule of water is removed, which results information of double bond. The product, phosphoenolpyruvate (PEP), has phosphate group attached by an unstable bond (wavy line).
Each of two PEP molecules transfers its phosphate groupto ADP to yield ATP and pyruvate. This is substrate-levelphosphorylation reaction.
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9
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Summary ReactionSummary Reaction
• Conversion of pyruvate to acetyl CoA
2 pyruvate + 2 coenzyme A + 2 NAD+ →
2 acetyl CoA + 2 CO2 + 2 NADH
Summary ReactionSummary Reaction
• Citric acid cycle
2 acetyl CoA + 6 NAD+ + 2 FAD + 2 ADP
+ 2 Pi + 2 H2O → 4 CO2 + 6 NADH +
2 FADH2 + 2 ATP + 2 CoA
Citric Acid Cycle in DetailCitric Acid Cycle in Detail
Summary ReactionsSummary Reactions
• Hydrogen atoms in ETC
NADH + 3 ADP + 3 Pi + 12 O2 → NAD+ +
3 ATP + H2O
FADH2 + 2 ADP + 2 Pi + 12 O2 → FAD + 2 ATP + H2O
Summary ReactionSummary Reaction
• Lactate fermentation
C6H12O6 → 2 lactate + energy (2 ATP)
Summary ReactionSummary Reaction
• Alcohol fermentation
C6H12O6 → 2 CO2 + 2 ethyl alcohol + energy (2 ATP)
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The Overall Reactions of The Overall Reactions of GlycolysisGlycolysis