This document summarizes a chapter on cellular respiration. It describes the four phases of cellular respiration: (1) glycolysis breaks down glucose to pyruvate, producing a small amount of ATP; (2) pyruvate is further oxidized to acetyl CoA, releasing carbon dioxide; (3) the citric acid cycle completely breaks down acetyl CoA, producing ATP and carbon dioxide; (4) the electron transport chain uses oxygen to release energy from electrons and produce most of the ATP through chemiosmosis. NAD+ and FAD act as electron carriers to shuttle electrons between reactions. Cellular respiration aerobically breaks down glucose and other nutrients to carbon dioxide and water, harvesting energy to produce large amounts of

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:
Section 6.1
Chapter 7: Photosynthesis

3. UNIT A 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.
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Chapter 6: Cellular Respiration
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?

4. UNIT A Chapter 6: Cellular Respiration Section 6.1
6.1 Overview of Cellular Respiration
In cellular respiration, molecules such as glucose are broken
down to release energy that is used to synthesize ATP.
•It is an aerobic process (requires oxygen) and produces
carbon dioxide
•Glucose (a high-energy molecule) is broken down to carbon
dioxide and water, which are low-energy molecules
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5. UNIT A Chapter 6: Cellular Respiration Section 6.1
Cellular Respiration
Energy from the
breakdown of glucose is
released in incremental
steps, and used to
synthesize ATP.
The energy in ATP is
used for many cell
reactions. The energy is
released by the breaking
of a bond and release of a
phosphate group.
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Figure 6.1 The breakdown of ATP releases energy,
which is used by cells to do work.

6. UNIT A Chapter 6: Cellular Respiration
Section 6.1
Oxidation and Reduction
Oxidation: an atom or molecule loses an electron
Reduction: an atom or molecule gains an electron
• The substance being oxidized is donating electrons and is
called the reducing agent. The substance being reduced is
accepting electrons and is called the oxidizing agent.
• Compounds or atoms contain more energy in their reduced
form than in their oxidized form.
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Figure 6.2 Oxidation and
reduction reactions take
place at the same time.

7. UNIT A Chapter 6: Cellular Respiration
Section 6.1
NAD+ and FAD
Some enzymes use the coenzymes NAD+ (nicotinamide
adenine dinucleotide) or FAD (flavin adenine dinucleotide),
which act as electron carriers in reactions.
•NAD+ receives two electrons and two H+, forming
NADH + H+
•FAD receives two electrons and two H+, forming FADH2
Figure 6.3 The
NAD+ cycle.
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8. UNIT A Chapter 6: Cellular Respiration
Section 6.1
Phases of Cellular Respiration
The four phases of cellular respiration: glycolysis, preparatory
reaction, citric acid cycle, and electron transport chain.
Figure 6.4 The four phases
of complete glucose
breakdown.
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9. UNIT A Chapter 6: Cellular Respiration
Section 6.1
Phases of Cellular Respiration
1. Glycolysis: breakdown of glucose (C6) to two molecules
of pyruvate (C3).
• There is a net gain of 2 ATP for every glucose
molecule broken down to pyruvate
• It is anaerobic, therefore oxygen is not required
1. Preparatory reaction: oxidation of pyruvate to a C2 acetyl
group with coenzyme A attached.
• Carbon dioxide is released
• It occurs twice per glucose molecule
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10. UNIT A Section 6.1
3. Citric acid cycle: a cyclical set of oxidation reactions that
break down pyruvate.
• The cycle produces carbon dioxide and one ATP per
turn of the cycle
• It turns twice since two acetyl-CoA molecules enter
per glucose molecule
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Chapter 6: Cellular Respiration
Phases of Cellular Respiration

11. UNIT A Section 6.1
Phases of Cellular Respiration
4. Electron transport chain: membrane-bound electron
carriers
• electrons pass between carriers
• energy is released, and the electrons become lower in
energy
• low-energy electrons are received by
O2, then H+ reacts to form H2O.
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Chapter 6: Cellular Respiration
Figure 6.5 Electron
transport chain.

12. UNIT A Section 6.1
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Chapter 6: Cellular Respiration
Check Your Progress
1. Explain the role of NAD+ and FAD in cellular
respiration.
2. Distinguish between the aerobic and anaerobic
phases of cellular respiration.
3. Summarize the location and function of each
phase of cellular respiration.

13. UNIT A Section 6.1
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Chapter 6: Cellular Respiration