CHAPTER 7 HARVESTING
ENERGY:
GLYCOLYSIS AND
CELLULAR
RESPIRATION
AT A GLANCE
Case Study: When Athletes Boost Their Blood Counts: Do Cheaters Prosper?
7.1
What Is the Source of a Cell’s Energy?
A. Glucose Is a Key Energy-Storage Molecule
B. Photosynthesis Is the Ultimate Source of Cellular Energy
C. Glucose Metabolism and Photosynthesis Are Complementary Processes
â Lecture Activity 7.1: Modeling Cell Respiration
7.2
How Do Cells Harvest Energy from Glucose? (Figure 7-1)
A. First Stage Is Glycolysis—Does Not Require Oxygen
1. Glycolysis breaks down glucose into 2 pyruvate molecules
a. Pyruvate may enter mitochondria and, if oxygen available, aerobic respiration will continue to
release 34 or 36 ATP
b. If no oxygen available: pyruvate does not enter mitochondria and fermentation occurs
7.3
What Happens during Glycolysis? (Figure 7-2)
â BioFlix: Cellular Respiration
â Web Animation: Glucose Metabolism
A. Glucose Activation Consumes Energy
B. Energy Harvest Yields Energy-Carrier Molecules
1. Glucose is converted to fructose biphosphate (unstable)
a. Energy input (activation)—2 ATP needed to initiate glucose breakdown
2. Fructose biphosphate splits to 2 glyceraldehyde-3-phosphate molecules (G3P)
3. Each G3P molecule converted a pyruvate molecule and 2 ATP released (4 ATP total)
a. During conversion of each G3P to pyruvate, 1 NADH molecule produced (2 NADH total)
When Athletes Boost Their Blood Counts: Do Cheaters Prosper? Continued
C. Summing Up: Glycolysis
7.4
What Happens during Cellular Respiration? (Figure 7-3)
A. Overview—Cellular Respiration Is Series of Aerobic Reactions Where Pyruvate (from
Glycolysis) Is Broken Down to CO2 and H2O
1. Two molecules of pyruvate produced by glycolysis are transported into the mitochondrion
2. Each three-carbon pyruvate splits into CO2 and two-carbon molecule and enters Krebs cycle
a. Krebs cycle produces 1 ATP for each pyruvate and donates electrons
3. Electrons are donated to electron transport chain
4. Energy of electrons in electron transport chain used to transport H + from matrix to
intermembrane compartment
5. End of electron transport chain, electrons combine with O 2 and H+ to form H2O
6. H+ ions move back across membrane, along concentration gradient
7. H+ ion flow provides energy to produce ATP
8. ATP moves into fluid of cytoplasm
B. The Krebs Cycle Breaks Down Pyruvate in the Mitochondrial Matrix (Figure 7-4)
1. In the mitochondrial matrix, pyruvate reacts with a molecule of coenzyme A to produce
acetyl-CoA and one CO2 and one NADH
2. Each acetyl-CoA combines with a molecule of oxaloacetate to produce six-carbon citrate,
releasing coenzyme A
3. Citric acid goes through a series of reactions to regenerate oxaloacetate
4. End products of the Krebs cycle per molecule of pyruvate: 2 CO 2, 1 ATP, 1 FADH2, and 3
NADH
C. Summing Up: The Mitochondrial Matrix Reactions
1. Final end products of mitochondrial matrix reactions per molecule of glucose: 6 CO2, 2 ATP, 8
NADH, and 2 FADH2
D. Energetic Electrons Are Carried to Electron Transport Chains (Figure 7-5)
1. From glycolysis and the mitochondrial matrix reactions, the cell has accumulated 4 ATP, 10
NADH, and 2 FADH2
2. The electron carriers, NADH and FADH2, donate their electrons to the electron transport
chains located in the inner mitochondrial membrane
3. Energy released by these electrons is used to pump hydrogen ions from the matrix into the
intermembrane compartment to produce ATP by chemiosmosis
4. Oxygen is the final electron acceptor and combines with hydrogen ions to form water
5. Without oxygen, electrons would pile up and ATP synthesis would stop
When Athletes Boost Their Blood Counts: Do Cheaters Prosper? Continued
E. Energy from a Hydrogen-Ion Gradient Is Used to Produce ATP
1. During chemiosmosis, the flow of hydrogen ions provides enough energy to produce 32–34
ATP
2. The ATP diffuses out of the mitochondria to the cytoplasm through the outer membrane, which is
permeable to ATP
F. Summing Up: Electron Transport and Chemiosmosis
â Lecture Activity 7.2: Mitochondrial Disorders
â Lecture Activity 7.3: Production of Carbon Dioxide in Respiration
7.5
What Happens during Fermentation? (Figure 7-5)
A. Some Cells Ferment Pyruvate to Form Alcohol (Figure 7-6)
1. Reactions of fermentation generate no ATP
2. Pyruvate produced by glycolysis acts as electron acceptor for NADH
a. Pyruvate converted to ethanol or lactate and NADH converted to NAD+
3. Regenerates NAD+ molecules needed for glycolysis
B. Other Cells Ferment Pyruvate to Lactate (Figure 7-8)
1. Occurs in microorganisms
a. For example, bacteria that produce yogurt, sour cream, and cheese
C. Fermentation’s Effects Limit Human Muscle Performance
1. When muscles are deprived of O2
a. Glycolysis continues for a while in absence of O2
b. Muscle cells then need to perform lactate fermentation to regenerate NAD +
c. Lactate buildup causes muscle fatigue
â Lecture Activity 7.4: Demonstration of Fermentation