CHAPTER 5
ESSENTIAL CONCEPTS OF METABOLISM
CHAPTER 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.
CHAPTER OBJECTIVES
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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.
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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.
CHAPTER 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.
Chemical reactions
1.
Metabolic pathways
2.
Catabolic pathways
3.
Anabolic pathways
II.
Enzymes
A.
General characteristics
B.
Properties of enzymes
1.
Activation energy
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2.
C.
D.
E.
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
Properties of coenzymes and cofactors
1.
Apoenzymes
2.
Holoenzymes
3.
Coenzymes
a.
NAD
b.
FAD
4. Cofactors
Enzyme inhibition
1.
Competitive inhibition
2.
Noncompetitive inhibition
3.
Allosteric site
4.
Feedback inhibition
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.
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
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D.
4. Anaerobic respiration – a bacterial alternative
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
Teaching Tips
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Video:
Enzymes: Regulators of Body Chemistry (40 min, C, VHS)
Examines mechanics of enzyme-substrate interactions. (BN96, IM)
Obtain or or have students make a simple model of an enzyme and a
substrate molecule to illustrate the lock-and-key feature.
Obtain photos of or draw the molecules NAD and FAD and note how
they are involved in oxidation and reduction. Reiterate the
ability of the molecules to exist in both oxidized and reduced
forms. Note the vitamin portion of the mollecules.
Video: Cellular Respiration (IBM) Reviews anaerobic and aerobic
processes. (L39211041B, PLP)
Video: Cellular Respiration (30 min, C, VHS) Computer animation
of glycolysis, the Krebs cycle, and ATP production. (BN491, IM)
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Have students bring various foods to class and have them try to
figure out how and where they contain energy.
Web Destinations
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http://www.liunet.edu/cwis/bklyn/acadres/facdev/FacultyProjects/W
ebClass/micro-web/html-files/ChapterC-1.html
Long Island University site covers bacterial metabolism
http://www.people.virginia.edu/~rjh9u/enrgysum.html
Robert J. Huskey site covers glycolysis and the Krebs cycle
http://biotech.icmb.utexas.edu/glycolysis/glycohome.html
This
site from the University of Texas provides an interactive link
through the process of glycolysis.
http://www.bact.wisc.edu/Microtextbook/TOC.html
On-line microbiology textbook
Discussion Topics
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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?
Track It Down
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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?
Additional Resources
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The Magic of Enzymes (30 min., C, 1996, VHS).
This video
explains the vital role of enzymes in human biology. (BZ 1141,
IM)
Cellular Respiration: Energy for Life (30 min., C, 1994, VHS).
The program examines the complex process by which cells convert
nutrients into energy. (BZ 491, IM)
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Cellular Respiration (60 min., C, VHS).
This six part series
examines the essential fuels and machinery used by living forms
to sustain themselves. (EXP3668, FFH)
Unseen Life on Earth: An Introduction to Microbiology Part 3 Metabolism (30 min., C, 1999, VHS). A 12-part series produced in
part by the American Society for Microbiology which explains
basic microbial principles and how microbes affect everything
from medicine to environmental issues to global politics.
(CA00125-ULSVE, CPB)
Enzymes (1996, CD-ROM).
This program describes the biological
importance of enzymes and how they work to sustain life.
(AAZ
31311, EDU)
Enzymes: Thoroughbred Workhorses of the Cell (24 min, C, VHS,
1994).
Explores phosphor fructose kinase action, specificity,
and catalysis. (99734, MG)
Energy (25 min, C, VHS).
Discusses the types, characteristics,
and role of energy in our lives. (99663, MG)
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