Chapter 5: Microbial Metabolism
What is Metabolism?
Metabolism = all chemical reactions that occur in a
cell/organism; catabolism + anabolism.
Catabolism = breakdown of food molecules to produce energy
and molecular subunits (example: amino acids from proteins)
Anabolism = building of macromolecules that the organism
needs (proteins from amino acid subunits or DNA from
nucleotides)
Metabolic (also called biochemical) pathways
http://www.expasy.ch/cgi-bin/show_thumbnails.pl
e1
A
e2
B
e3
C
D
Feedback inhibition = shutting off of biochemical pathway;
product in pathway binds to e1 which changes its shape and
stops its work
Enzymes
Type of molecule – usually proteins; a few RNA molecules
called ribozymes too.
Words ending with –ase are enzymes
Shape determines function
Active site
E = enzyme, S = substrate, P = product
E+S
ES
E+P
Enzyme catalyzed reactions
Enzyme-substrate complexes
What affects enzyme activity?




Temperature
pH
Concentration of substrate
Inhibitors
Ex. Folic acid pathway
Sulfanilamide competes with PABA;
no folic acid made
Ex. Fluoride in drinking water and toothpaste
inhibit cavity-causing bacteria
Denaturation of proteins
How temperature, pH, and substrate concentration affect enzyme activity --
How inhibitors work --
Energy molecules in cells
ATP  ADP + Pi
NADH  NAD+ + H+ + 2eFADH2  FAD + 2H+ + 2e-
Catabolism of Glucose
Aerobic respiration – efficient energy production (1
glucose converted to 38 ATP)
2. Anaerobic respiration – less efficient (less than 38 ATP); no oxygen
3. Fermentation – least efficient (2 ATP produced); usually without
oxygen
1.
Aerobic Respiration
Process:
Start molecule
End molecule
Energy molecules
produced
Waste
Glycolysis
Glucose
Pyruvate
2 NADH
2 ATP
--
Oxidation of pyruvate
Pyruvate
Acetyl-CoA
2 NADH
2 CO2
Krebs cycle
(citric acid cycle)
Acetyl-CoA
--
6 NADH
2 ATP
2 FADH2
4 CO2
Electron transport
chain/chemiosmosis
NADH
FADH2
NAD+
FAD
ATP
Water
Anaerobic respiration
 Uses parts of all of the aerobic processes (but not all)
 Final electron acceptor not oxygen
 Possible e- acceptors:
Nitrogen compounds NO3-  NO2, N2O, N2
Sulfur compounds SO4-2  H2S
Carbon compounds CO3-2  CH4
Fermentation
 Only produces 2 ATP molecules from 1 glucose
 Occurs without oxygen (O2)
 Detour from glycolysis to a short fermentation pathway
 Produces by-products as NAD+ and FAD are regenerated
 By-products produced include acids, alcohols, gases, etc.
Practical example:
Fact: Clostridium perfringens causes gas gangrene
Problem: How to cure gas gangrene…
Patients affected: Anyone with an anaerobic site of tissue damage;
diabetics particularly prone to this disease
(Diabetics have poor circulation, nerve damage, lessened pain
sensations, lower ability to heal)
Diagnosis: Odors, specimen collection and identification of
bacteria, X-ray for pockets of gas in tissues
Treatment: Essential -- Remove dead tissue (sometimes even
amputation of affected limb); Possible -- expose tissues to oxygen
through a hyperbaric chamber and/or antibiotic regimen
This photomicrograph reveals Clostridium perfringens grown in Schaedler’s
broth using Gram-stain. (Photo by CDC/Don Stalons, 1974.)
Wagner Grade 5 - Unsalvagable Gangrene
Gangrene or necrosis to the extent that the foot is beyond
salvage and will require a major limb- or life-sparing
amputation.
http://www.squidoo.com/diabeticfoot
Why do microbes have the ability to switch back
and forth between aerobic respiration and an
anaerobic process?
Process
Advantages
Disadvantages
Aerobic respiration
Makes many ATPs from 1
glucose
Requires oxygen;
produces oxygen free radicals
Anaerobic processes
(fermentation or anaerobic
respiration)
Survival without oxygen
Makes less ATP from glucose;
slower growth; d
etrimental waste products
What about other food sources
besides glucose?
What about anabolic reactions?
The End