Download Overview of the reactions of cellular synthesis and

Introduction: biosynthesis
.
The combined processes whereby the major constituents of the bacterial
cell are synthesized is called biosynthesis.
In the last lecture we covered the production of ATP and NAD(P)H from
light and an electron donor. These are required in autotrphic CO2 fixation
(plants and bacteria) which is the ultimate sustainer of all food chains. Do
not forget the nitrogen, sulphur, phosphate, iron and trace elements.
Carbon dioxide is the primary substrate supporting life and is incorporated
into cells by different mechanisms. In this lecture we will look at, some
carbon fixation mechanisms and the assimilation of nitrogen and sulphur.
Overview of the reactions of cellular synthesis
and biodegradation
Biosynthesis
Heterotrophic bacteria
Chemoorganotrophic bacteria can utilize a wide range of carbon compounds
(sugars from polysaccharides, amino acids from proteins, nucleotides from DNA
and RNA etc.) as energy sources. All of these bacteria use the same
compounds or derivatives thereoff as carbon sources. Then they are called
Heterotrophic bacteria.
The basic principles are often illustrated by using glucose as an example.
The major pathways for the degradation of carbohydrates and the tricarboxylic
acid cycle are used as a source of precursor molecules for the biosynthesis of
cell material.
EmbdenMeyerhof
(EM)
pathway, or
glycolysis
Entner-Doudoroff (ED) pathway
Krebs cycle, or tricarboxylic acid (TCA) cycle
Hexose monophosphate shunt (HMS), or
pentose phosphate pathway
Feeling adventurous ?
• Go to ”Encyclopedia of Escherichia coli
Genes and Metabolism” at
http://biocyc.org/ for full details of all
known pathways in Escherichia coli and
some other bacteria.
superpathway of leucine, valine, and isoleucine
biosynthesis
The glyoxylate cycle
The glyoxylate cycle is a special case for organisms growing on a C2 carbon
compound (Example Eschericia coli growing on acetate) and new enzymes are
required to incorporate this substrate.
Glyoxylate cycle
Biosynthesis
Autotrophic bacteria
Autotrophic bacteria use carbon dioxide as their sole source of carbon.
Most of the chemolithotrophic and photosynthetic bacteria are autotrophic. The
mathanogenic archaea are also autotrophic.
The Calvin cycle for CO2 fixation is the most widespread pathway of CO2
fixation, but it is only found in aerobic or aerotolerant bacteria.
Some bacteria specializing in the metabolism of C1 compounds (methane,
methanol, methylamine) have special pathways.
Several different pathways for CO2 fixation are found in the strict anaerobic
bacteria (Green sulphur bacteria) and archaea (methanogens).
Calvin cycle
Biosynthesis
Autotrophic bacteria
Autotrophic bacteria use carbon dioxide as their sole source of carbon.
Most of the chemolithotrophic and photosynthetic bacteria are autotrophic. The
mathanogenic archaea are also autotrophic.
The Calvin cycle for CO2 fixation is the most widespread pathway of CO2 fixation,
but it is only found in aerobic or aerotolerant bacteria.
Some bacteria specializing in the metabolism of C1 compounds (methane,
methanol, methylamine) have special pathways.
Several different pathways for CO2 fixation are found in the strict anaerobic
bacteria (Green sulphur bacteria) and archaea (methanogens).
Pathways of carbon assimilation in methaneusing organisms
Pathways of carbon assimilation in methaneusing organisms
Biosynthesis
Autotrophic bacteria
Autotrophic bacteria use carbon dioxide as their sole source of carbon.
Most of the chemolithotrophic and photosynthetic bacteria are autotrophic. The
mathanogenic archaea are also autotrophic.
The Calvin cycle for CO2 fixation is the most widespread pathway of CO2 fixation,
but it is only found in aerobic or aerotolerant bacteria.
Some bacteria specializing in the metabolism of C1 compounds (methane,
methanol, methylamine) have special pathways.
Several different pathways for CO2 fixation are found in the strict anaerobic
bacteria (Green sulphur bacteria) and archaea (methanogens).
The reductive citric acid pathway, present in green
sulfur and a few other bacteria
Present in green sulfur
bacteria (Chlorobium
limicola), thermophilic
hydrogen-oxidizing bacteria
(Hydrogenobacter
thermophilus), and some of
the sulfate-reducing
bacteria (Desulfobacter
hydrogenophilus).
Pathway of CO2 fixation in acetogenic bacteria
This pathway is
present in
homoacetogenic
bacteria (Clostridium
thermoaceticum),
most of the sulfatereducing bacteria
(Desulfobacterium
autotrophicum), and
selected
methanogenic
archaea
(Methanosarcina
barkeri). THF,
tetrahydrofolic acid;
[Cor]E, vitamin B12
corrinoid enzyme.
Carbon fixation in Chloroflexus.
Chloroflexus is considered to have a very old pathway for the fixation of
CO2.
There are very few atrains of this bacteria and the hydroxypropionate
pathway is very unusual in so much that it is not found in any other species
of bacteria or archaea.
The hydroxypropionate pathway, present in
Chloroflexus.
Assimilation of ammonia
Nitrogen is a major constituent of biological molecules
Some bacteria and archaea can fix atmospheric nitrogen, dinitrogen N2
and the product is ammonia. This process will be described later in the
course when we meet these organisms.
Many bacteria and archaea can reduce nitrate to ammonia (assimilative
nitrate reduction) for biosynthetic purposes. This is not to be confused
with dissimilative nitrate reduction in which nitrate is used a a terminal
electron acceptor in energy metabolism.
Inorganic nitrogen in the form of ammonia is converted to organic
nitrogen in glutamate and glutamine. These amino acids are then the
major donors of organic nitrogen most biosynthetic reactions.
Assimilation of ammonia
Together, the
glutamate
dehydrogenase and
glutamine synthetase
reactions result in the
assimilation of two
ammonia molecules
(shown as the
ammonium ion, NH4+).
Transamination reaction
The glutamate-dependent transamination of an α-keto acid is a fundamental
reaction of amino acid synthesis.
Assimilation of sulphur
Sulphur is a major constituent of biological molecules
Many bacteria and archaea can reduce sulphate to hydrogen sulphide
(assimilative sulphate reduction) for biosynthetic purposes. This is not to
be confused with dissimilative sulphate reduction in which sulphate is
used a a terminal electron acceptor in energy metabolism by the
”Sulphate reducing bacteria”.
Inorganic sulphur, in the form of hydrogen sulphide, is used directly in
most biosynthetic reactions.
Sulphur assimilation
Sulfate is assimilated
through the production of
sulfide (S2-), which is then
used in the synthesis of
organic sulfur-containing
compounds.
Origin of the nine atoms in the purine ring
Origin of the six atoms in the pyrimidine ring
Biosynthesis of a fatty acid I
Biosynthesis of a fatty
acid
Biosynthesis of phospholipids
Biosynthesis of phospholipids
Synthesis of cell structures from glucose