CHAPTER 5

ESSENTIAL CONCEPTS OF METABOLISM

FChapter Overview

An important characteristic of all living organisms is their ability to produce energy from a wide variety of foodstuffs and to use this energy to synthesize necessary materials. When it was discovered that microbes could metabolize a wide variety of materials, many phenomena, such as the souring of milk, the production of alcohol in fruit juices, and the spoilage of meats, were explained. These metabolic characteristics of microbes led to other discoveries and ultimately to the use of microbes for industrial production of a wide variety of chemicals, byproducts, enzymes, and the like. An understanding of metabolic systems is essential for the development of industrial uses of microorganisms. This chapter provides an overview of the characteristics of the pathways that microbes use to accomplish their metabolic activities.

Glycolysis, the Krebs cycle, electron transport, and the chemiosmosis systems are described and illustrated with examples to show how they are involved in producing some important substances used in industry, in agriculture, and for human consumption.

The last section explains the importance and relationships of other metabolic processes seen in environmentally important microbes.

FChapter Objectives

  • Define: metabolism, autotrophy, heterotrophy, oxidation, reduction, photoautotrophy, photoheterotrophy, chemoautotrophy, hemoheterotrophy, glycolysis, fermentation, aerobic metabolism, and biosynthetic processes
  • List and describe the characteristics of enzymes and explain how these characteristics contribute to enzymatic function.
  • List and describe the characteristics of a coenzyme, noting especially its relationship to an enzyme.
  • List the basic steps of the glycolysis pathway, noting especially the location of energy production, the role of coenzymes, and the significance of pyruvic acid.
  • List several important characteristics of fermentation.
  • Describe the Krebs cycle, and explain its significance in energy capture.
  • Describe the electron transport chain, noting especially the processes of oxidative phosphorylation and chemiosmosis and their significance in energy capture.
  • Contrast the metabolic processes of fermentation and aerobic metabolism, noting especially the cycles involved, energy production, type of oxidation, and the end products.
  • Describe how microorganisms metabolize fats and proteins for energy.
  • Briefly describe the process of photosynthesis and explain its significance in photoheterotrophic and photoautotrophic microbes.
  • Contrast the processes of photoheterotrophy and chemo-autotrophy.
  • Describe how bacteria carry out biosynthetic activities and relate these activities to their amphibolic pathways.
  • List and describe several examples of how bacteria use energy for membrane transport and for movement.
  1. Animations and videos – online
  2. Cellular respiration
  3. Lew-Port’s Biology Place All About Enzymes animation
  4. Enzyme animation
  5. Enzyme animation from Wiley
  6. John Kryk’s website on glycolysis
  7. John Kryk’s website on Krebs citric acid cycle
  8. John Kryk’s website on the electron transport system
  9. Annenberg Foundation (registration required) video on metabolism -
  10. Graham Kent’s website from Smith College animations on the different steps involved in aerobic respiration and photosynthesis -

 Web Destinations

This site from the University of Texas provides an interactive link through the process of glycolysis.


  • On-line microbiology textbook

Energy, enzymes, and catalysis problem set from the University of Arizona’s Biology Project website.

Animations and video on the electron transport chain.

Glycolysis animation from Cornell

Cellular respiration and fermentation from the University of Cincinnati Clermont College

 Discussion Topics

  • Everyone knows you can eat a doughnut and gain energy. Where is the energy in the doughnut, and how is it converted to useable energy such as heat, motion, and electricity?
  • Why is it important for enzymes to have a high degree of specificity?

 Potential essay questions

  • New microbes have been genetically altered to "eat" very unusual substances, such as complex oils and oil sludge. How has this been accomplished?
  • How can phototrophic bacteria be of value to the environment even though they do not produce oxygen?
  • What importance does bioluminescence have to organisms that live in total darkness?

FChapter Outline

I.Metabolism: An Overview

A.Metabolism

1.Anabolism

2.Catabolism

B.Electron transfer

1.Oxidation

2.Reduction

C.Autotrophy

1.Photoautotrophy

2.Chemoautotrophy

D.Heterotrophy

1.Photoheterotrophs

2.Chemoheterotrophs

a.Glycolysis

b.Fermentation

c.Aerobic respiration

E.Relationship of respiration to photosynthesis

F.Metabolic pathways

1.Catabolic pathways

2.Anabolic pathways

II.Enzymes

A.General characteristics

B.Properties of enzymes

1.Activation energy

2.Reaction surface

a.Active site

b.Substrates

c.Enzyme-substrate complex

3.Specificity

4.Classification of enzymes

5.Location of action

a. Endoenzymes

b. Exoenzymes

C.Properties of coenzymes and cofactors

1.Apoenzymes

2.Holoenzymes

3.Coenzymes

a.NAD

b.FAD

4. Cofactors

D.Enzyme inhibition

1.Competitive inhibition

2.Noncompetitive inhibition

3.Allosteric site

4.Feedback inhibition

E.Factors that affect enzyme reactions

1.Temperature and pH

2.Concentration

III.Anaerobic Metabolism: Glycolysis and Fermentation

A.Glycolysis

1.Phosphorylation

2.Breakage of glucose

3.Role of NAD

4.Formation of ATP

B.Alternatives to glycolysis

C. Fermentation

1.Homolactic-acid fermentation

2.Alcoholic fermentation

3.Other kinds of fermentations

4.Special diagnostic tests

IV.Aerobic Metabolism: Respiration

A.Role of glycolysis

B.The Krebs cycle

1.Formation of acetyl-CoA

2.Removal of hydrogen atoms

3.Special events

C.Electron transport and oxidative phosphorylation

1.Electron transport chain

2.Oxidative phosphorylation

3.Chemiosmosis

4.Anaerobic respiration – a bacterial alternative

D.Significance of energy capture

V.Metabolism of Fats and Proteins

A.Fat metabolism

B.Protein metabolism

VI.Other Metabolic Processes

A.Photoautotrophy

1.Photosynthesis

a.Light reactions

b.Dark reactions

2.Photosynthetic bacteria

3.Eukaryote comparisons

B.Photoheterotrophy

C.Chemoautotrophy

1.Basic characteristics

2.Chemolithotrophic bacteria

VII.Uses of Energy

A.Biosynthetic activities

1.Amphibolic pathways

2.Other biosynthetic processes

B.Membrane transport and movement

1.Membrane transport

a.Active transport

b.Phosphotransferase system

2.Movement

C.Bioluminescence

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