1. How Cells Harvest Chemical Energy
Chapter 6
How Cells Harvest Chemical Energy

2. How Is a Marathoner Different from a Sprinter?
How Is a Marathoner Different from a Sprinter?
Human muscles contain two different types of muscle fibers
That perform differently under different conditions

3. The different types of muscle fibers
Function either aerobically, with oxygen, or anaerobically, without oxygen
Cellular respiration
Is the process by which cells produce energy aerobically

4. INTRODUCTION TO CELLULAR RESPIRATION
6.1 Photosynthesis and cellular respiration provide energy for life
Cellular respiration makes ATP and consumes O2
During the oxidation of glucose to CO2 and H2O

5. Photosynthesis uses solar energy
Photosynthesis uses solar energy
To produce glucose and O2 from CO2 and H2O
CO2
H2O
Glucose O2
ATP
ECOSYSTEM
Sunlight energy
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
(for cellular work)
Heat energy +
Figure 6.1

6. 6.2 Breathing supplies oxygen to our cells and removes carbon dioxide
6.2 Breathing supplies oxygen to our cells and removes carbon dioxide
Breathing provides for the exchange of O2 and CO2
Between an organism and its environment
CO2 O2
Bloodstream
Muscle cells carrying out
Cellular Respiration
Breathing
Glucose + O2
CO2 +H2O +ATP
Lungs
Figure 6.2

7. 6.3 Cellular respiration banks energy in ATP molecules
6.3 Cellular respiration banks energy in ATP molecules
Cellular respiration breaks down glucose molecules
And banks their energy in ATP
C6H12O6
CO2 6
H2O
ATPs
Glucose
Oxygen gas
Carbon dioxide
Water
Energy O2 +
Figure 6.3

8. 6.4 The human body uses energy from ATP for all its activities
CONNECTION
6.4 The human body uses energy from ATP for all its activities
ATP powers almost all cellular and body activities
Table 6.4

9. Table 6.4 Energy Consumed by Various Activities (in kcal).

10. 6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen
Electrons lose potential energy
During their transfer from organic compounds to oxygen

11. When glucose is converted to carbon dioxide
When glucose is converted to carbon dioxide
It loses hydrogen atoms, which are added to oxygen, producing water
C6H12O6
6 O2
6 CO2
6 H2O
Loss of hydrogen atoms (oxidation)
Gain of hydrogen atoms (reduction)
Energy
(ATP)
Glucose +
Figure 6.5A

12. And transfers them to NAD+ (reduction)
Dehydrogenase removes electrons (in hydrogen atoms) from fuel molecules (oxidation)
And transfers them to NAD+ (reduction) O H 2H
Reduction
Dehydrogenase
(carries
2 electrons)
NAD+
2H+
2e
NADH H+
Oxidation +
Figure 6.5B

13. Electron transport chain
NADH passes electrons
To an electron transport chain
As electrons “fall” from carrier to carrier and finally to O2
Energy is released in small quantities
H2O
NAD+
NADH
ATP H+
Controlled release of energy for synthesis of ATP
Electron transport chain 2 O2
2e + 1
Figure 6.5C

14. STAGES OF CELLULAR RESPIRATION AND FERMENTATION
6.6 Overview: Cellular respiration occurs in three main stages
Cellular respiration
Occurs in three main stages

15. Stage 1: Glycolysis
Occurs in the cytoplasm
Breaks down glucose into pyruvate, producing a small amount of ATP

16. Stage 2: The citric acid cycle
Takes place in the mitochondria
Completes the breakdown of glucose, producing a small amount of ATP
Supplies the third stage of cellular respiration with electrons

17. Stage 3: Oxidative phosphorylation
Occurs in the mitochondria
Uses the energy released by “falling” electrons to pump H+ across a membrane
Harnesses the energy of the H+ gradient through chemiosmosis, producing ATP

18. An overview of cellular respiration
An overview of cellular respiration
NADH
FADH2
GLYCOLYSIS
Glucose
Pyruvate
CITRIC ACID CYCLE
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Substrate-level phosphorylation
Oxidative phosphorylation
Mitochondrion
and
High-energy electrons carried by NADH
ATP
CO2
Cytoplasm
Figure 6.6

19. 6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
In glycolysis, ATP is used to prime a glucose molecule
Which is split into two molecules of pyruvate
NAD+
NADH H+
Glucose
2 Pyruvate
ATP 2 P
2 ADP +
Figure 6.7A

20. Organic molecule (substrate)
Glycolysis produces ATP by substrate-level phosphorylation
In which a phosphate group is transferred from an organic molecule to ADP
Enzyme
Adenosine
Organic molecule (substrate)
ADP
ATP P
Figure 6.7B

21. Acetyl CoA (acetyl coenzyme A)
6.8 Pyruvate is chemically groomed for the citric acid cycle
Prior to the citric acid cycle
Enzymes process pyruvate, releasing CO2 and producing NADH and acetyl CoA
CO2
Pyruvate
NAD+
NADH
+ H+
CoA
Acetyl CoA (acetyl coenzyme A)
Coenzyme A
Figure 6.8 2 1 3

22. 6.9 The citric acid cycle completes the oxidation of organic fuel, generating many NADH and FADH2 molecules
In the citric acid cycle
The two-carbon acetyl part of acetyl CoA is oxidized
CoA
CO2
NAD+
NADH
FAD
FADH2
ATP P
CITRIC ACID CYCLE
ADP + 3 +
3 H+
Acetyl CoA 2
Figure 6.9A

23. The two carbons are added to a four-carbon compound, forming citrate
Which is then degraded back to the starting compound

24. For each turn of the cycle Two CO2 molecules are released
The energy yield is one ATP, three NADH, and one FADH2
and
Steps
CITRIC ACID CYCLE
Oxaloacetate
CoA
2 carbons enter cycle
Acetyl CoA
Citrate
leaves cycle
+ H+
NAD+
NADH
CO2
Alpha-ketoglutarate
ADP P
ATP +
Succinate
FAD
FADH2
Malate
Step
Acetyl CoA stokes the furnace.
NADH, ATP, and CO2 are generated during redox reactions.
Redox reactions generate FADH2 and NADH.
Figure 6.9B 1 5 2 4 3

25. 6.10 Most ATP production occurs by oxidative phosphorylation
6.10 Most ATP production occurs by oxidative phosphorylation
Electrons from NADH and FADH2
Travel down the electron transport chain to oxygen, which picks up H+ to form water
Energy released by the redox reactions
Is used to pump H+ into the space between the mitochondrial membranes

26. Driving the synthesis of ATP
In chemiosmosis, the H+ diffuses back through the inner membrane through ATP synthase complexes
Driving the synthesis of ATP
Intermembrane space
Inner mitochondrial membrane
Mitochondrial matrix
Protein complex
Electron flow
Electron carrier
NADH
NAD+
FADH2
FAD
H2O
ATP
ADP
ATP synthase H+ + P O2
Electron Transport Chain
Chemiosmosis .
OXIDATIVE PHOSPHORYLATION
+ 2 1 2
Figure 6.10

27. Cyanide, carbon monoxide
CONNECTION
6.11 Certain poisons interrupt critical events in cellular respiration
Various poisons
Block the movement of electrons
Block the flow of H+ through ATP synthase
Allow H+ to leak through the membrane H+ O2
H2O P
ATP
NADH
NAD+
FADH2
FAD
Rotenone
Cyanide, carbon monoxide
Oligomycin
DNP
ATP Synthase + 2
ADP
Electron Transport Chain
Chemiosmosis 1
Figure 6.11

28. Cyanide, carbon monoxide Oligomycin
Rotenone
Cyanide,
carbon monoxide
Oligomycin H+ H+
ATP
synthase H+ H+ H+ H+ H+
DNP
FADH2
FAD
Figure 6.11 The effects of five poisons on the electron transport chain and chemiosmosis. 1  2 O2
+ 2 H+
NADH
NAD+ H+
ADP + P
ATP H+
H2O H+
Electron Transport Chain
Chemiosmosis

29. OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
6.12 Review: Each molecule of glucose yields many molecules of ATP
Oxidative phosphorylation, using electron transport and chemiosmosis
Produces up to 38 ATP molecules for each glucose molecule that enters cellular respiration
Electron shuttle across membrane
Mitochondrion
Cytoplasm 2
NADH 2
NADH
(or 2 FADH2) 2
NADH 6
NADH 2
FADH2
GLYCOLYSIS
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Glucose 2
2 Acetyl CoA
CITRIC ACID CYCLE
Pyruvate
+ 2 ATP
+ 2 ATP
+ about 34 ATP
by substrate-level phosphorylation
by substrate-level phosphorylation
by oxidative phosphorylation
About 38 ATP
Maximum per glucose:
Figure 6.12

30. 6.13 Fermentation is an anaerobic alternative to cellular respiration
6.13 Fermentation is an anaerobic alternative to cellular respiration
Under anaerobic conditions, many kinds of cells
Can use glycolysis alone to produce small amounts of ATP

31. In lactic acid fermentation
In lactic acid fermentation
NADH is oxidized to NAD+ as pyruvate is reduced to lactate
2 Lactate
NAD+
NADH 2
ATP
2 ADP + 2
2 Pyruvate
GLYCOLYSIS P
Glucose
Figure 6.13A

32. In alcohol fermentation
In alcohol fermentation
NADH is oxidized to NAD+ while converting pyruvate to CO2 and ethanol
NAD+
NADH 2
GLYCOLYSIS
2 ADP + 2 P
ATP
Glucose
2 Pyruvate
released
CO2
2 Ethanol
Figure 6.13B
Figure 6.13C

33. INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN AND SYNTHESIS
6.14 Cells use many kinds of organic molecules as fuel for cellular respiration

34. OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Carbohydrates, fats, and proteins can all fuel cellular respiration
When they are converted to molecules that enter glycolysis or the citric acid cycle
OXIDATIVE PHOSPHORYLATION (Electron Transport and Chemiosmosis)
Food, such as peanuts
Carbohydrates
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
Glucose
G3P
Pyruvate
Acetyl CoA
CITRIC ACID CYCLE
ATP
GLYCOLYSIS
Figure 6.14

35. 6.15 Food molecules provide raw materials for biosynthesis
6.15 Food molecules provide raw materials for biosynthesis
Cells use some food molecules and intermediates from glycolysis and the citric acid cycle as raw materials
This process of biosynthesis
Consumes ATP
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
G3P
Glucose
Amino
groups
Amino acids
Fatty
acids
Glycerol
Sugars
Carbohydrates
Fats
Proteins
Cells, tissues, organisms
Figure 6.15

36. 6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth
Glycolysis is the universal energy-harvesting process of living organisms
So, all cells can use glycolysis for the energy necessary for viability
The fact that glycolysis has such a widespread distribution is good evidence for evolution
Ancient prokaryotes probably used glycolysis to make ATP long before oxygen was present in Earth’s atmosphere.
Student Misconceptions and Concerns
1. Perhaps more than anywhere else in general biology, students studying aerobic metabolism may fail to see the forest for the trees. Students may focus on the details of each stage of aerobic metabolism and devote little attention to the overall process and products. Consider emphasizing the products and energy yields associated with glycolysis, the citric acid cycle, and oxidative phosphorylation before detailing the specifics of each reaction.
2. The location within a cell in which each reaction takes place is often forgotten in the details of the chemical processes, but it is important to emphasize. Consider using Figure 6.12 as a common reference to locate each stage as you discuss the details of cellular respiration.
3. Students frequently think that plants have chloroplasts instead of mitochondria. Take care to point out the need for mitochondria in plants when photosynthesis is not efficient or possible (such as during the night).
Teaching Tips
1. The widespread occurrence of glycolysis, which takes place in the cytosol and independent of organelles, suggests that this process had an early evolutionary origin. Since atmospheric oxygen was not available in significant amounts during the early stages of Earth’s history, and glycolysis does not require oxygen, it is likely that this chemical pathway was used by the prokaryotes in existence at that time. Students focused on the evolution of large, readily apparent structures such as wings and teeth may have never considered the evolution of cellular chemistry.
Copyright © 2009 Pearson Education, Inc.

37. 6.16 The fuel for respiration ultimately comes from photosynthesis
6.16 The fuel for respiration ultimately comes from photosynthesis
All organisms
Can harvest energy from organic molecules
Plants, but not animals
Can also make these molecules from inorganic sources by the process of photosynthesis
Figure 6.16

38. You should now be able to
Explain how photosynthesis and cellular respiration are necessary to provide energy that is required to sustain your life
Explain why breathing is necessary to support cellular respiration
Describe how cellular respiration produces energy that can be stored in ATP
Explain why ATP is required for human activities
Copyright © 2009 Pearson Education, Inc.

39. You should now be able to
Describe the process of energy production from movement of electrons
List and describe the three main stages of cellular respiration
Describe the major steps of glycolysis and explain why glycolysis is considered to be a metabolic pathway
Copyright © 2009 Pearson Education, Inc.

40. You should now be able to
Describe the citric acid cycle as a metabolic pathway designed for generating additional energy from glucose
Discuss the importance of oxidative phosphorylation in producing ATP
Describe useful applications of poisons that interrupt critical steps in cellular respiration
Copyright © 2009 Pearson Education, Inc.

41. You should now be able to
Compare respiration and fermentation
Provide evidence that glycolysis evolved early in the history of life on Earth
Discuss the mechanisms that cells use to biosynthesize cell components from food
Copyright © 2009 Pearson Education, Inc.