Diversity of Metabolism in Procaryotes (page 8)
(This chapter has 8 pages)
© Kenneth Todar, PhD
The pathways of central metabolism (i.e., glycolysis and the TCA
with a few modifications, always run in one direction or another in all
organisms. The reason - these pathways provide the precursors for the
of cell material. When a pathway, such as the Embden-Meyerhof pathway
the TCA cycle, functions to provide energy in addition to chemical
for the synthesis of cell material, the pathway is referred to as an amphibolic
pathway. Pathways of glycolysis and the TCA cycle are amphibolic
because they provide ATP and chemical intermediates to build new cell
The main metabolic pathways, and their relationship to biosynthesis of
cell material, are shown in Figure 25 below.
Biosynthesis or intermediary metabolism is a topic of
biochemistry, more so than microbiology. It will not be dealt with in
here. The fundamental metabolic pathways of biosynthesis are similar in
all organisms, in the same way that protein synthesis or DNA structure
are similar in all organisms. When biosynthesis proceeds from central
as drawn below, some of the main precursors for synthesis of
cell structures and components are as follows.
Polysaccharide capsules or inclusions are polymers of glucose
and other sugars.
Cell wall peptidoglycan (NAG and NAM) is derived from glucose
Amino acids for the manufacture of proteins have
sources, the most important of which are pyruvic acid, alpha
ketoglutaric acid and oxalacetic acid.
Nucleotides (DNA and RNA) are synthesized from
phosphate. ATP and NAD are part of purine
Triose-phosphates are precursors of glycerol, and acetyl
CoA is a main precursor of lipids for membranes
Vitamins and coenzymes are synthesized in various
that leave central metabolism. In the example given in Figure 25,
heme synthesis proceeds from the serine pathway, as well as from
succinate in the TCA cycle.
Figure 25. The main pathways
of biosynthesis in procaryotic cells
END OF CHAPTER
Return to Page 1
Previous Page | Textbook of Bacteriology Index