Biology 12 - Cellular Respiration - Section 6-1

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

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?

6.1 Overview of Cellular RespirationIn 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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Cellular RespirationEnergy 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.

Oxidation and ReductionOxidation: an atom or molecule loses an electronReduction: 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.

NAD+ and FADSome 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

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Figure 6.3 The NAD+ cycle.

Phases of Cellular RespirationThe four phases of cellular respiration: glycolysis, preparatory reaction, citric acid cycle, and electron transport chain.

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Figure 6.4 The four phases of complete glucose breakdown.

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

2. 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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Phases of Cellular Respiration

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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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 byO2, then H+ reacts to form H2O.

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Figure 6.5 Electron transport chain.


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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.

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Science

Biology 12 - Cellular Respiration - Section 6-1