Diversity of Metabolism in
Procaryotes
Eli Komalawati
10406028
Bakteriologi BM-3204
Introduction
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The unicellular eucaryotes (protista) exhibit a fair amount of
structural diversity, but the procaryotes (bacteria and archaea) lack
this distinction.
There are a few basic morphologies, the possibilities of motility and
resting cells (spores), and a major differential stain (the Gram stain)
that differentiates procaryotes microscopically.
Biochemical or metabolic diversity, especially as it relates to
energy-generating metabolism and biosynthesis of secondary
metabolites.
The diversity of procaryotes is expressed by their great variation in
modes of energy generation and metabolism, and this feature allows
procaryotes to flourish in all habitats suitable for life on earth.
Energy-Generating Metabolism
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Metabolism :
catabolism : energy-generating
anabolism : energy-consuming
Catabolic reactions produce
energy as ATP, which can be
utilized in anabolic reactions
to build cell material from
nutrients in the environment.
Figure 1. The relationship between catabolism and anabolism
ATP
ATP - adenosine triphosphate : the universal currency of
energy exchange in biological systems.
Figure 2. The structure of ATP
NAD
NAD (Nicotinamide Adenine Dinucleotide) : coenzyme
commonly involved in energy-producing metabolism
Figure 3. The Structure of NAD
Coenzyme A
Coenzyme A is involved in a type of ATP-generating reaction
seen in some fermentative bacteria and in all respiratory
organisms.
Figure 4. (a) The Structure of
Coenzyme A. CoA-SH is a
derivative of ADP. The molecule
shown here attached to ADP is
pantothenic acid, which carries
a terminal thiol (-S) group. (b)
the oxidation of the keto acid,
pyruvic acid, to acetyl~SCoA.
ATP Synthesis in Procaryotes
Cells fundamentally can produce ATP in two ways :
1. substrate level phosphorylation : ATP is made during the
conversion of an organic molecule from one form to another
2. electron transport phosphorylation : drive electrons
through an electron transport system (ETS) in the membrane,
establish a proton motive force (pmf), and use the pmf to
synthesize ATP
Substrate Level Phosphorylation
Figure 5. Three examples of
substrate level phosphorylation.
(a) and (b) are the two substrate
level phosphorylations that occur
during the Embden Meyerhof
pathway, but they occur in all
other fermentation pathways
which have an Embden-Meyerhof
component. (c) is a substrate
level phosphorylation found in
Clostridium and Bifidobacterium.
These are two anaerobic
(fermentative) bacteria who
learned how to make one more
ATP from glycolysis beyond the
formation of pyruvate.
Electron Transport Phosphorylation
Figure 6. The plasma membrane
of Escherichia coli.
Heterotrophic Types of Metabolism
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Heterotrophy is the use of an organic compound as a source
of carbon and energy.
Heterotrophic bacteria are the masters of decomposition and
biodegradation in the environment.
Heterotrophic metabolism is driven mainly by two metabolic
processes : fermentations and respirations.
1. Fermentation : metabolism in which energy is derived from
the partial oxidation of an organic compound using organic
intermediates as electron donors and electron acceptors. All
ATP is produced by substrate level phosphorylation.
Figure 7. Model fermentation
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In procaryotes there exist three major pathways of glycolysis
(the dissimilation of sugars):
Embden-Meyerhof pathway, which is also used by most
eucaryotes, including yeast (Saccharomyces);
Phosphoketolase or heterolactic pathway related to the
hexose-pentose shunt;
Entner-Doudoroff pathway
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The Embden-Meyerhof Pathway
Figure 8. The
Embden Meyerhof
pathway for glucose
dissimilation.
Figure 9. (a) The Embden Meyerhof pathway of lactic acid fermentation
in lactic acid bacteria (Lactobacillus) and (b) the Embden Meyerhof
pathway of alcohol fermentation in yeast (Saccharomyces).
Bacterial fermentations are distinguished by their end products
into the following groups :
No.
Groups
End Product
Bacteria
1.
Homolactic
Fermentation
Lactic acid
homolactic acid bacteria
(Lactobacillus, Lactococcus and
most streptococci)
2.
Mixed Acid
Fermentations
A mixture of lactic acid, acetic acid,
formic acid, succinate and ethanol,
gases (CO2 and H2)
Enterobacteriaceae
2a.
Butanediol
Fermentation
Mixed acids and gases, 2,3
butanediol, acetoin
Enterobacteriaceae
3.
Butyric acid
fermentations
Butyric acid, acetic acid, CO2 and H2
clostridia
3a.
Butanol-acetone
fermentation
Butanol and acetone
Clostridium acetobutylicum
4.
Propionic acid
fermentation
Propionate, acetic acid, CO2 and
propionic acid
propionic acid bacteria which
include corynebacteria,
Propionibacterium and
Bifidobacterium
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The Heterolactic (Phosphoketolase) Pathway
Figure 10. The heterolactic
(phosphoketolase) pathway
of fermentation. The overall
reaction in the fermentation
of glucose is Glucose ------> Lactic acid + ethanol +
CO2 + 1 ATP (net).
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The Entner-Doudoroff Pathway
Figure 11. The EntnerDoudoroff Pathway of
Fermentation.
The overall reaction is
Glucose -------> 2
ethanol + 2 CO2 + 1 ATP
(net).
2. Respiration : result in the complete oxidation of the substrate by
an outside electron acceptor.
Besides pathway of glycolysis, four essential metabolic components are
needed :
1. The tricarboxylic acid (TCA) cycle (Kreb's cycle): used for the
complete oxidation of the substrate. The end product is CO2.
2. A membrane and an associated electron transport system (ETS).
3. An outside electron acceptor. For aerobic respiration the electron
acceptor is O2. But in anaerobic respiration, the final electron
acceptors may be SO4 or S or NO3 or NO2 or fumarate.
4. A transmembranous ATPase enzyme (ATP synthetase). This enzyme
utilizes the proton motive force established on the membrane to
synthesize ATP in the process of electron transport phosphorylation.
Figure 12. Model of aerobic respiration.
Lithotrophic Types of Metabolism
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Lithotrophy is the use of an inorganic compound as a source
of energy.
physiological group
energy source
organism
H2
oxidized end
product
H2O
hydrogen bacteria
methanogens
H2
H2O
Methanobacterium
carboxydobacteria
CO
CO2
Rhodospirillum, Azotobacter
nitrifying bacteria*
NH3
NO2
Nitrosomonas
nitrifying bacteria*
NO2
NO3
Nitrobacter
sulfur oxidizers
H2S or S
SO4
Thiobacillus, Sulfolobus
iron bacteria
Fe ++
Fe+++
Gallionella, Thiobacillus
Alcaligenes, Pseudomonas
* The overall process of nitrification, conversion of NH3 to NO3, requires a consortium of
microorganisms.
Table 2. Physiological groups of lithotrophs
Phototrophic Metabolism
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Phototrophy is the use of light as a source of energy for
growth, more specifically the conversion of light energy into
chemical energy in the form of ATP.
Procaryotes that can convert light energy into chemical energy
include the photosynthetic cyanobacteria, the purple and green
bacteria and the "halobacteria" (actually archaea).
Autotrophic CO2 fixation
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Use CO2 as a source of carbon for growth by using RUBP
carboxylase and the Calvin cycle for CO2 fixation.
Figure 22. The Calvin cycle and its relationship to the synthesis of cell materials.
Biosynthesis
Figure 25. The main pathways of
biosynthesis in procaryotic cells
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