Metabolic pathway

1. Metabolic pathways with
particular relevance to
environmental biotechnology

2. Only through an understanding of the microorganisms' energy -yielding and
energy-consuming reactions can we create the conditions that lead to
environmental
protection and improvement
the overall strategy of environmental biotechnology is to make use of the
metabolic path ways in micro-organisms to break down or metabolise organic
material .
 Metabolic pathways operating in the overall direction of synthesis are termed
anabolic while those operating in the direction of breakdown or degradation
are described as catabolic: the terms catabolism and anabolism being applied
to describe the degradative or synthetic processes respectively

3. Metabolism: Sum total of all chemical processes of a cell.
Catabolism: All processes involved in the oxidation of substrates or use of sunlight in
order to obtain energy.
Anabolism: All processes for the synthesis of cellular components from carbon sources.
The transfer of energy between catabolism and anabolism is termed energy coupling.
• The chemical energy released during oxidation of substrates (catabolism) is transferred
by energy coupling, usually through a coenzyme such as ATP.
• The ATP energy is given up for anabolic processes such as cell growth or maintenance.
Cells obtain energy for growth and maintenance either through oxidation of chemicals
(chemotrophs) or through photosynthesis (phototrophs).
In catabolism by chemotrophs, either organic materials (chemoorganotrophs) or inorganic
materials (chemolithotrophs) are oxidized for energy.

4. Carbon in biomolecules
Enters central metabolic pathways
Glycolysis, TCA cycle, Glyoxylate cycle

5. Three basic stages of organic catabolism in
chemoorganotrophs

6. Glyoxylate cycle
 This is principally the TCA cycle, with two additional steps forming a ‘short
circuit’, involving the formation of glyoxalate from isocitrate. The second reaction
 requires the addition of acetyl CoA to glyoxalate to produce malic acid and thus rejoin the TCA
cycle. The purpose of this shunt is to permit the organism to use acetyl CoA, which is the major
breakdown product of fatty acids, as its sole carbon source.

8. benefits
It is bypass reaction of TCA cycle
It occurs in bacteria when they are cultured in acetate rich
carbon source.
When Higher fattyacids are oxidized into acetylcoA without
forming puruvate acids, then acetylcoA enters into
glyoxylate cycle.

9. Catabolism of lipids
 Their catabolism is by hydrolysis of the fatty acids from the glycerol backbone,
followed by oxidation of the fatty acids by β-oxidation. This process releases
glycerol which may then be further degraded by feeding into the central pathways
of glycolysis, and several units of the acetyl group attached to the carrier Coenzyme A which
may feed into the central metabolic pathways
just prior to entry into the TCA cycle
Compound lipids include the phosphoglycerides which are a major component
of cell membranes. These can have very bulky polar head groups and nonpolar
tails which allow them to act as surfactants and in this specific context, biosurfactants.

11. biosurfactants

12. Protein hydrolysis
 The first catabolic step in protein degradation is enzymatic hydrolysis of the peptide
bond formed during protein synthesis resulting in the release of short pieces, or
peptides, and eventually after further degradation, amino acids. The primary step in
amino acid catabolism is to remove the amino group thus producing an α-keto acid.
This is usually achieved by transfer of the amino group to the TCA cycle intermediate,
α-ketoglutarate, resulting in the amino acid, glutamate.
 The α-keto acid resulting from deamination of the amino acid is degraded by a series
of reactions, the end product being dependent on the original amino acid, but all will
finally result as a glycolysis or TCA cycle intermediate

13. Catabolism of nucleic acids
 Degradation of nucleic is also a source of ammonium ion.
 The purines are broken down to release CO2 and uric acid which is
reduced to allantoin. This is then hydrolysed to produce urea and
glyoxylate which can enter the TCA cycle by the glyoxylate pathway
present in plants and bacteria but not mammals. The urea thus produced
may be further hydrolysed to ammonium ion or ammonia with the release
of carbon dioxide.
The form in which the nitrogen derived from the purines is excreted, again
depends upon the organism. Pyrimidines are hydrolysed to produce
ammonia which enters the nitrogen
cycle, carbon dioxide and β-alanine or β-aminoisobutyric acid both of which
are
finally degraded to succinyl CoA which enters the TCA cycle.

14. • Catabolism depends on the oxidation and reduction of chemicals in the organism's environment.
• Oxidation removes electrons, and reduction adds electrons.
• Materials that are oxidized are called electron donors, and those being reduced are electron
acceptors.
• For an rganism to obtain energy, it must be furnished with an electron donor and an electron
acceptor.
• The electron donor is considered to be the energy substrate or "food“ for the microorganisms.
• Common electron donors: Compounds containing carbon in a reduced state (organic chemicals) or
containing other elements in a reduced state (reduced inorganic compounds, such as ammonia,
hydrogen, or sulfide).

15. • Common electron acceptors: oxygen, nitrate, nitrite, Fe(III), sulfate, and carbon dioxide.
• Newer (unconventional) electron acceptors (of interest in environmental context):
chlorate, perchlorate, chromate, selenate, and chlorinated organics such as
tetrachloroethylene and chlorobenzoate.
Illustration of energy generation
through redox reactions

16. • The chemical energy captured in ATP is used by the cell for cell synthesis and maintenance.
• ATP diffuses through the cell, and whenever the energy it contains is needed, the cell
extracts the energy, releasing a phosphate molecule and converting the ATP into ADP.
Energy coupling via ATP

17. Anabolism
• Anabolism is the suite of metabolic processes leading to cell synthesis.
• Simple chemical precursors (like acetate) are converted into a set of more complex building blocks
(like glucose), which are then assembled into the macromolecules that comprise proteins,
carbohydrates, lipids, nucleic acids, and any other cell component.
• Two basic options for anabolism: Heterotrophy and Autotrophy
• In heterotrophy, an organic compound, generally one with two or more carbon atoms, is used as
the main source of cell carbon.
• In autotrophy, inorganic carbon is used as the sole basic carbon source, although small amounts
of organic compounds such as vitamins may also be required.
• Some organisms can grow either autotrophically or heterotrophically, a situation called
mixotrophy.

18. • The energy required to synthesize cellular components from organic carbon is very
much less than that for synthesis from inorganic carbon.
• Over eight times more energy is required to synthesize a 6-carbon sugar from carbon
dioxide than from acetate.
• The energy required for cellular growth directly comes from the ATP synthesized during
catabolism.
• The pathways and processes involved in converting carbon dioxide into glucose by
autotrophs was demonstrated by Melvin Calvin and his colleagues in what has become
known as the Calvin cycle.

19. Calvin cycle