Dr. Lamees A.Razzak
Metabolism of Microorganisms:-
Metabolism:Refers to the sum of the biochemical reactions required for energy generation and
the use of energy to synthesize cell material from small molecules in the
environment. Metabolism consists of catabolism and anabolism reactions:1-Anabolism reactions:Are energy-requiring subset of metabolic reactions, which synthesize large
molecules from smaller ones.
1- Catabolism reactions:Are the energy–releasing subset of metabolic reactions, which degrade or
breakdown large molecules into smaller ones.
*ATP (adenosine triphosphate):During catabolism, useful energy is temporarily conserved in the "high energy
bond" of ATP. When energy is required during anabolism, it may be spent as the high
energy bond of ATP which has a value of about 8 kcal per mole. Hence, the
conversion of ADP to ATP requires 8 kcal of energy, and the hydrolysis of ATP to
ADP releases 8 kcal.
*NAD (Nicotinamide Adenine Dinucleotide):Another coenzyme commonly involved in energy-producing metabolism, derived
from the vitamin niacin, is the pyridine nucleotide, NAD. The basis for chemical
transformations of energy usually involves oxidation/reduction reactions. For a
biochemical to become oxidized, electrons must be removed by an oxidizing agent.
The oxidizing agent is an electron acceptor that becomes reduced in the reaction.
During the reaction, the oxidizing agent is converted to a reducing agent that can add
its electrons to another chemical, thereby reducing it, and oxidizing itself. The
molecule that usually functions as the electron carrier in these types of coupled
oxidation-reduction reactions in biological systems is NAD and its phosphorylated
derivative, NADP. NAD or NADP can become alternately oxidized or reduced by the
loss or gain of two electrons. The oxidized form of NAD is symbolized NAD; the
reduced form is symbolized as
NADH, NADH2 or NADH + H+.
*Metabolism is best considered in three stages:1. Energy metabolism, 2. Respiratory metabolism, 3. Biosynthetic pathways
Energy metabolism
Energy used by bacteria is primarily produced by fermentative and/ or respiratory
metabolic pathways.
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*Anaerobic metabolism (fermentative metabolism)
Glycolytic ( Embden-Meyerhof ) pathway:Is a multistep process in which one glucose molecule is converted to numerous
compound through a metabolic pathway (such as Embden-Meyerhof pathway) to
yield 2 molecules of pyruvic acid and 2 ATP molecules.
As a result of glycolysis four ATP molecules are produced. However, 2 ATP
molecules were initially invested in pathway and the net gain is therefore 2 ATP
molecules.
The two molecules of pyruvic acid then be utilized for ATP production through
the reaction of Krebs cycle and electron transport to yield 36 ATP or they may be
utilized in fermentation.
Fermentation:Is a metabolism pathway that not involve oxygen. In fermentation specific
enzymes take the pyruvic acid molecules and convert them to acids (acetic acid,
butyric acid, and lactic acid), alcohol and other end product depend upon which
enzyme is present and which organism is producing the enzyme.
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Fermentation is a way to obtain the two molecules of ATP per molecule of
glucose metabolized through glycolysis. If oxygen were present, fermentation would
not occur and the pyruvic acid would be utilized in Krebs cycle.
*Aerobic metabolism ( respiration):Include Krebs cycle, involves the metabolism of 2-carbon groups to carbon
dioxide and water and the production of ATP
*Biosynthetic pathways:The role of metabolism in biosynthetic include:1- Used to build small molecules with nitrogen, sulphur and other minerals into
amino acids, purines, pyrimidines, polysaccharides and lipids
2- Uses of energy
For biosynthetic activities e.g. cell wall synthesis, protein synthesis, nucleic acid
synthesis etc. Membrane transport and movement e.g active transportation.
3- Uses of metabolic products in the laboratory
Metabolic end products e.g. pyruvic acid, lactic acid, mixed gases, alcohols, are
used for bacterial identification. (Biochemical tests) e.g. oxidase tests, catalase tests
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