This document outlines chapters and sections from a textbook on cell biology and cellular respiration. It describes glycolysis, the breakdown of glucose into pyruvate that occurs in the cytoplasm. Glycolysis has an energy-investment phase that uses ATP and an energy-harvesting phase that produces ATP. It also describes fermentation, which takes over under anaerobic conditions, converting pyruvate into lactate or ethanol. Fermentation allows glycolysis to continue but yields much less ATP than aerobic respiration.

2. UNIT A: Cell Biology
Chapter 2: The Molecules of Cells
Chapter 3: Cell Structure and Function
Chapter 4: DNA Structure and Gene
Expression
Chapter 5: Metabolism: Energy and
Enzymes
Chapter 6: Cellular Respiration:
Sections 6.2, 6.3
Chapter 7: Photosynthesis

3. UNIT A Chapter 6: Cellular Respiration
Chapter 6: Cellular Respiration
In this chapter you will learn about the many chemical reactions,
known as cellular respiration, that break down molecules such as
glucose to produce the ATP that fuels physical activities.
Why are there differences
between the aerobic and
anaerobic pathways?
How is the energy of a
glucose molecule harvested by
a cell?
How are other organic
nutrients, such as proteins and
fats, used as energy?
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4. UNIT A Chapter 6: Cellular Respiration Section 6.2
6.2 Outside the Mitochondria: Glycolysis
Glycolysis is the breakdown of glucose to pyruvate in the
cytoplasm.
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5. UNIT A Chapter 6: Cellular Respiration
Section 6.2
Energy-Investment Steps
At the beginning of glycolysis
•two ATP are used to activate glucose
•the phosphorylated glucose molecule splits into two C3
molecules, which are often referred to G3P
•After this point, each G3P molecule undergoes the same
reactions
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6. UNIT A Chapter 6: Cellular Respiration
Section 6.2
Energy-Harvesting Steps
Once G3P is formed:
•G3P is oxidized and NAD+ is reduced to NADH + H+ (will
pass e− to transport chain)
•Oxidation of G3P and subsequent substrates results in four
high-energy phosphate groups
•The high-energy phosphate groups are used to synthesize
four ATP made by substrate-level ATP synthesis
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7. UNIT A Chapter 6: Cellular Respiration
Section 6.2
Figure 6.6
Glycolysis
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8. UNIT A Chapter 6: Cellular Respiration
Section 6.3
Inputs and Outputs of Glycolysis
Each glucose that
enters glycolysis
forms
•two ATP
•two NADH + H+
•two pyruvate
• When oxygen is available, pyruvate enters the
mitochondria for further breakdown
• When oxygen is limited, fermentation occurs
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9. UNIT A Chapter 6: Cellular Respiration
Section 6.2
Check Your Progress
1. Explain why there is an energy-investment phase
and an energy-harvesting phase to glycolysis.
2. Summarize the inputs and outputs of glycolysis
and state the net number of ATP that are produced.
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10. UNIT A Chapter 6: Cellular Respiration
Section 6.2
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11. UNIT A Chapter 6: Cellular Respiration
Section 6.3
6.3 Outside the Mitochondria:
Fermentation
When oxygen is limited, anaerobic pathways such as
fermentation are used.
•In humans and other animals, pyruvate is reduced to
lactate in a process called lactic acid fermentation
•In other organisms, such as yeast, pyruvate undergoes
reduction and loss of CO2, to produce alcohol in a process
called alcoholic fermentation
•The NAD+ produced from reduction of pyruvate can be
used in glycolysis
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12. UNIT A Chapter 6: Cellular Respiration
Section 6.3
Fermentation
Figure 6.7 Fermentation.
Fermentation consists of
glycolysis followed by a
reduction of pyruvate by
NADH + H+. The resulting
NAD+ returns to the
glycolytic pathway to pick
up more hydrogen atoms.
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13. UNIT A Section 6.3
Advantages and Disadvantages of Fermentation
Advantages:
•Provides a rapid burst of ATP and is especially useful in
muscle cells during exertion when oxygen is in limited supply
Disadvantages:
•Lactate is toxic to cells. Its build-up in tissues changes the
pH and causes muscles to “burn.” Recovery is only complete
when the lactate has been transported to the liver where it is
converted to pyruvate, which is broken down
•There is a low yield of ATP
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Chapter 6: Cellular Respiration

14. UNIT A Section 6.3
Energy Yield of Fermentation
Fermentation produces two ATP per glucose molecule.
This represents a small fraction of the potential 30-32 ATP
that can be produced from complete breakdown of glucose by
cellular respiration.
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Chapter 6: Cellular Respiration

15. UNIT A Section 6.3
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Chapter 6: Cellular Respiration
Check Your Progress
1. Describe the environmental conditions that
would cause a muscle cell to undergo
fermentation.
2. Explain how fermentation acts as a NAD+
recycling system.

16. UNIT A Section 6.3
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Chapter 6: Cellular Respiration