Biology 12 - Glycolysis and Fermentation - Section 6-2 and 6-3

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

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.

UNIT A Chapter 6: Cellular Respiration

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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?

6.2 Outside the Mitochondria: GlycolysisGlycolysis is the breakdown of glucose to pyruvate in the cytoplasm.

UNIT A Chapter 6: Cellular Respiration Section 6.2

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UNIT A Section 6.2

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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

Energy-Investment Steps

UNIT A Section 6.2

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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

Energy-Harvesting Steps

UNIT A Section 6.2

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Figure 6.6 Glycolysis

Inputs and Outputs of Glycolysis

• When oxygen is available, pyruvate enters the mitochondria for further breakdown

• When oxygen is limited, fermentation occurs

UNIT A Section 6.3

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Each glucose that enters glycolysis forms•two ATP•two NADH + H+ •two pyruvate

UNIT A Section 6.2

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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.

UNIT A Section 6.2

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6.3 Outside the Mitochondria: FermentationWhen 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

UNIT A Section 6.3

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Fermentation

UNIT A Section 6.3

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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.

Advantages and Disadvantages of FermentationAdvantages: •Provides a rapid burst of ATP and is especially useful in muscle cells during exertion when oxygen is in limited supplyDisadvantages: •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

UNIT A Section 6.3

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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.

UNIT A Section 6.3

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UNIT A Section 6.3

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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.

UNIT A Section 6.3

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Science

Biology 12 - Glycolysis and Fermentation - Section 6-2 and 6-3