How Cells make ATP: Energy-Releasing Pathways How Cells make ATP: Energy-Releasing Pathways Chapter 8

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


• 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


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


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


• Aerobic respiration consists of four stages: glycolysis, formation of acetyl coenzyme A, the citric acid cycle, and the electron transport chain and chemiosmosis


• 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


Pyruvate

2 ATP 2 ATP 32 ATP


• 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


• 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


• 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.


• 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


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


• Nutrients other than glucose, including many carbohydrates, lipids, and amino acids, can be oxidized by aerobic respiration


• 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)


• 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


• 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


• 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


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.

8

9

10


• Conversion of pyruvate to acetyl CoA

2 pyruvate + 2 coenzyme A + 2 NAD+ →

2 acetyl CoA + 2 CO2 + 2 NADH


• 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


• Lactate fermentation

C6H12O6 → 2 lactate + energy (2 ATP)


• Alcohol fermentation

C6H12O6 → 2 CO2 + 2 ethyl alcohol + energy (2 ATP)

CLICKTO PLAY

The Overall Reactions of The Overall Reactions of GlycolysisGlycolysis

Documents

How Cells make ATP: Energy-Releasing Pathways How Cells make ATP: Energy-Releasing Pathways Chapter 8