Chapter 7: Cellular Pathways That Harvest Chemical Energy CHAPTER 7 Cellular Pathways That Harvest Chemical Energy

Chapter 7: Cellular Pathways That Harvest Chemical Energy

CHAPTER 7Cellular Pathways That

Harvest Chemical Energy


Chapter 7: Cellular Pathways That Harvest Chemical EnergyObtaining Energy and Electrons from GluObtaining Energy and Electrons from Glucosecose

An Overview: Releasing Energy from GluAn Overview: Releasing Energy from Glucosecose

GlycolysisGlycolysis: From Glucose to : From Glucose to PyruvatePyruvate

PyruvatePyruvate Oxidation Oxidation

The Citric Acid CycleThe Citric Acid Cycle


Chapter 7: Cellular Pathways That Harvest Chemical EnergyThe Respiratory Chain: Electrons, Proton The Respiratory Chain: Electrons, Proton Pumping, and ATPPumping, and ATP

Fermentation: ATP from Glucose, withoutFermentation: ATP from Glucose, without O O

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Contrasting Energy YieldsContrasting Energy Yields

Metabolic PathwaysMetabolic Pathways

Regulating Energy PathwaysRegulating Energy Pathways


Cellular Pathways

• Metabolic pathways occur in small Metabolic pathways occur in small steps, each catalyzed by a specific steps, each catalyzed by a specific enzyme.enzyme.

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Cellular Pathways

• Metabolic pathways are often Metabolic pathways are often compartmentalized and are highly compartmentalized and are highly regulated.regulated.

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Obtaining Energy and Electrons from Glucose• When glucose burns, energy is When glucose burns, energy is

released as heat and light:released as heat and light:

CC66HH1212OO66 + 6 O + 6 O22 6 CO 6 CO22 + 6 H + 6 H220 + energy0 + energy

The same equation applies to the The same equation applies to the metabolism of glucose by cells, but the metabolism of glucose by cells, but the

reaction is accomplished in many reaction is accomplished in many separate steps so that the energy can separate steps so that the energy can

be captured as ATP. be captured as ATP.

Review Figure 7.1Review Figure 7.166


Figure 7.1

Figure 7.1Figure 7.1

figure 07-01.jpg


Obtaining Energy and Electrons from Glucose • As a material is oxidized, the electrons it As a material is oxidized, the electrons it

loses transfer to another material, which is loses transfer to another material, which is thereby reduced. thereby reduced.

• Such redox reactions transfer a lot of energy. Such redox reactions transfer a lot of energy.

• Much of the energy liberated by the oxidation Much of the energy liberated by the oxidation of the reducing agent is captured in the of the reducing agent is captured in the reduction of the oxidizing agent. reduction of the oxidizing agent.

• Review Figure Review Figure 7.27.2

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Figure 7.2


figure 07-02.jpg


Obtaining Energy and Electrons from Glucose

• The coenzyme NAD is a key electron The coenzyme NAD is a key electron carrier in biological redox reactions. carrier in biological redox reactions.

• It exists in two forms, one oxidized It exists in two forms, one oxidized (NAD(NAD++) and the other reduced (NADH ) and the other reduced (NADH + H+ H++). ).

Review Figures Review Figures 7.37.3, , 7.47.4

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Figure 7.3


figure 07-03.jpg


Figure 7.4


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An Overview: Releasing Energy from Glucose

• Glycolysis operates in the presence or Glycolysis operates in the presence or absence of Oabsence of O22. .

• Under aerobic conditions, cellular Under aerobic conditions, cellular respiration continues the breakdown respiration continues the breakdown process. process.

Review Figure Review Figure 7.57.5

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Figure 7.5 – Part 1

Figure 7.5 – Part 1Figure 7.5 – Part 1

figure 07-05a.jpg




figure 07-05b.jpg



• Pyruvate oxidation and the citric acid Pyruvate oxidation and the citric acid cycle produce COcycle produce CO22 and hydrogen and hydrogen atoms carried by NADH and FADHatoms carried by NADH and FADH22. .

• The respiratory chain combines the The respiratory chain combines the hydrogens with Ohydrogens with O22, releasing enough , releasing enough energy for ATP synthesis. energy for ATP synthesis.

Review Figure 7.5aReview Figure 7.5a1616



• In some cells under anaerobic In some cells under anaerobic conditions, pyruvate can be reduced conditions, pyruvate can be reduced by NADH to form lactate and by NADH to form lactate and regenerate the NAD needed to sustain regenerate the NAD needed to sustain glycolysis. glycolysis.

Review Figure 7.5bReview Figure 7.5b

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An Overview: Releasing Energy from Glucose • In eukaryotes, glycolysis and In eukaryotes, glycolysis and

fermentation occur in the cytoplasm fermentation occur in the cytoplasm outside of the mitochondria; pyruvate outside of the mitochondria; pyruvate oxidation, the citric acid cycle, and the oxidation, the citric acid cycle, and the respiratory chain operate in association respiratory chain operate in association with mitochondria. with mitochondria.

• In prokaryotes, glycolysis, fermentation, In prokaryotes, glycolysis, fermentation, and the citric acid cycle take place in and the citric acid cycle take place in the cytoplasm; and pyruvate oxidation the cytoplasm; and pyruvate oxidation and the respiratory chain operate in and the respiratory chain operate in association with the plasma membrane. association with the plasma membrane.

Review Table 7.1Review Table 7.11818


Table 7.1

Table 7.1Table 7.1

table 07-01.jpg


Glycolysis: From Glucose to Pyruvate

• Glycolysis is a pathway of ten enzyme-Glycolysis is a pathway of ten enzyme-catalyzed reactions located in the catalyzed reactions located in the cytoplasm. cytoplasm.

• It provides starting materials for both It provides starting materials for both cellular respiration and fermentation. cellular respiration and fermentation.


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Figure 7.6


figure 07-06.jpg


Glycolysis: From Glucose to Pyruvate • Glycolysis uses two ATPs for activation Glycolysis uses two ATPs for activation

energy & yields two PGAL’s. energy & yields two PGAL’s. • Two NADH molecules are produced, Two NADH molecules are produced,

and four ATP molecules are generated. and four ATP molecules are generated. • Two pyruvates are produced for each Two pyruvates are produced for each

glucose molecule. glucose molecule.

Review Figures 7.6, 7.7Review Figures 7.6, 7.7

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figure 07-07a.jpg




figure 07-07b.jpg




figure 07-07c.jpg


Pyruvate Oxidation

• The pyruvate dehydrogenase complex The pyruvate dehydrogenase complex catalyzes three reactions: catalyzes three reactions: Pyruvate is oxidized to the acetyl Pyruvate is oxidized to the acetyl

group, releasing one COgroup, releasing one CO22 molecule molecule and energy;and energy;

Some of this energy is captured when Some of this energy is captured when NADNAD++ is reduced to NADH + H is reduced to NADH + H++;;

The remaining energy is captured The remaining energy is captured when the acetyl group combines with when the acetyl group combines with coenzyme A, yielding acetyl CoA. coenzyme A, yielding acetyl CoA.

Review Figure 7.8Review Figure 7.8, 7.9a, 7.9a2626


Figure 7.8


figure 07-08.jpg


The Citric Acid Cycle

• The energy in acetyl CoA drives the The energy in acetyl CoA drives the reaction of acetate with oxaloacetate reaction of acetate with oxaloacetate to produce citrate. to produce citrate.

• The citric acid cycle is a series of The citric acid cycle is a series of reactions in which citrate is oxidized reactions in which citrate is oxidized and oxaloacetate regenerated. and oxaloacetate regenerated.

• It produces two COIt produces two CO22 , one FADH , one FADH22, three , three NADH, and one ATP for each acetyl NADH, and one ATP for each acetyl CoA. CoA.

Review Figures 7.9Review Figures 7.9bb, 7.10, 7.102828




figure 07-09a.jpg




figure 07-09b.jpg


Figure 7.10


figure 07-10.jpg


The Respiratory Chain: Electrons, Proton Pumping, and ATP• NADH + HNADH + H++ and FADH and FADH22 are oxidized by are oxidized by

the respiratory chain, regenerating the respiratory chain, regenerating NADNAD++ and FAD. and FAD.

• The enzymes and electron carriers of The enzymes and electron carriers of the chain are part of the inner the chain are part of the inner mitochondrial membrane. mitochondrial membrane.

• OO22 is the final acceptor of electrons is the final acceptor of electrons and protons, forming Hand protons, forming H22O. O.



Figure 7.11


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Figure 7.12


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The Respiratory Chain: Electrons, Proton Pumping, and ATP • The chemiosmotic mechanism couples The chemiosmotic mechanism couples

proton transport to ADP oxidative proton transport to ADP oxidative phosphorylation. phosphorylation.

• As electrons move along the As electrons move along the cytochromes, they lose energy cytochromes, they lose energy

• Proton pumps actively transport HProton pumps actively transport H++ out out of the mitochondrial matrix, establishing of the mitochondrial matrix, establishing a gradient of proton concentration and a gradient of proton concentration and electric charge—the proton-motive electric charge—the proton-motive force. force.





figure 07-13a.jpg




figure 07-13b.jpg


The Respiratory Chain: Electrons, Proton Pumping, and ATP • The proton-motive force causes The proton-motive force causes

protons to diffuse back into the protons to diffuse back into the mitochondrial interior through the mitochondrial interior through the membrane channel protein ATP membrane channel protein ATP synthase, which couples that diffusion synthase, which couples that diffusion to the production of ATP. to the production of ATP.


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Figure 7.14 – Part Figure 7.14 – Part 11

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Fermentation: ATP from Glucose, without O2• Many organisms and some cells live Many organisms and some cells live

without Owithout O22, deriving energy from , deriving energy from glycolysis and fermentation. glycolysis and fermentation.

• Together, these pathways partly Together, these pathways partly oxidize glucose and generate energy-oxidize glucose and generate energy-containing products. containing products.

• Fermentation reactions anaerobically Fermentation reactions anaerobically oxidize the NADH + Hoxidize the NADH + H++ produced in produced in glycolysis. glycolysis.



Figure 7.15


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Figure 7.16


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Contrasting Energy Yields

• For each molecule of glucose used, For each molecule of glucose used, fermentation yields 2 molecules of fermentation yields 2 molecules of ATP. ATP.

• In contrast, aerobic respiration yields In contrast, aerobic respiration yields up to 36. up to 36.


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figure 07-17a.jpg




figure 07-17b.jpg


Metabolic Pathways• Catabolic pathways feed into the Catabolic pathways feed into the

respiratory pathways. respiratory pathways. • Polysaccharides are broken down into Polysaccharides are broken down into

glucose, which enters glycolysis. glucose, which enters glycolysis. • Glycerol from fats also enters Glycerol from fats also enters

glycolysis, and acetyl CoA from fatty glycolysis, and acetyl CoA from fatty acids enters the citric acid cycle. acids enters the citric acid cycle.

• Proteins enter glycolysis and the citric Proteins enter glycolysis and the citric acid cycle via amino acids. acid cycle via amino acids.



Figure 7.18


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Figure 7.19


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Metabolic Pathways

• Anabolic pathways use intermediate Anabolic pathways use intermediate components of respiratory metabolism components of respiratory metabolism to synthesize fats, amino acids, and to synthesize fats, amino acids, and other molecules. other molecules.


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Regulating Energy Pathways• The rates of glycolysis and the citric The rates of glycolysis and the citric

acid cycle are regulated by the actions acid cycle are regulated by the actions of ATP, ADP, NADof ATP, ADP, NAD++, or NADH + H, or NADH + H++ on on allosteric enzymes.allosteric enzymes.

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Regulating Energy Pathways • Inhibition of the glycolytic enzyme Inhibition of the glycolytic enzyme

phosphofructokinase by abundant ATP phosphofructokinase by abundant ATP slows glycolysis. slows glycolysis.

• ADP activates this enzyme.ADP activates this enzyme.• The citric acid cycle enzyme isocitrate The citric acid cycle enzyme isocitrate

dehydrogenase is inhibited by ATP and dehydrogenase is inhibited by ATP and NADH and activated by ADP and NADNADH and activated by ADP and NAD++. .


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Figure 7.20


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Documents

Chapter 7: Cellular Pathways That Harvest Chemical Energy CHAPTER 7 Cellular Pathways That Harvest Chemical Energy