Synthesis of amino acids is critical for cell survival. They not only serve as the building blocks for proteins but also as starting points for the synthesis of many important cellular molecules including vitamins and nucleotides.

1. By
Dr. Akhilesh Kumar
Biosynthesis of Amino Acids

2. Figure: Overview of amino acid biosynthesis. The carbon
skeleton precursors derive from three sources: glycolysis
(pink), the citric acid cycle (blue), and the pentose
phosphate pathway (purple).
All amino acids are derived from intermediates in
glycolysis, the citric acid cycle, or the pentose phosphate
pathway. Nitrogen enters these pathways by way of
glutamate and glutamine.
Synthesis of amino acids is critical for cell
survival. They not only serve as the building
blocks for proteins but also as starting
points for the synthesis of many important
cellular molecules including vitamins and
nucleotides.

3. α-Ketoglutarate Gives Rise to Glutamate, Glutamine, Proline, and Arginine
Biosynthesis of serine from 3-phosphoglycerate and the subsequent
conversion of serine into glycine. Glycine is also made from CO2 and
NH4
+ by the action of glycine synthase, which uses N5,N10-
methylenetetrahydrofolate as methyl group donor

4. Serine, Glycine, and Cysteine are 3-Phosphoglycerate family
Biosynthesis of cysteine from homocysteine and serine in mammals.

5. Alanine and aspartate are synthesized from pyruvate and oxaloacetate, respectively, by transamination from
glutamate. Asparagine is then synthesized by amidation of aspartate, with glutamine donating the NH4
+ . These amino acids
are nonessential and their simple biosynthetic pathways are found in all organisms.
The amino acids methionine, threonine, lysine, isoleucine, valine, and leucine are essential amino acids. The biosynthetic
pathways for these amino acids are complex and interconnected. In some cases there are significant differences in the
pathways present in bacteria, fungi, and plants.
Aspartate gives rise to methionine, threonine, and lysine. Branch points occur at aspartate-β-semialdehyde, an
intermediate in all three pathways, and at homoserine, a precursor of threonine and methionine. Threonine, in turn, is one
of the precursors of isoleucine. The valine and isoleucine pathways share four enzymes. Pyruvate gives rise to valine and
isoleucine in pathways that begin with the condensation of two carbons of pyruvate (in the form of hydroxyethyl thiamine
pyrophosphate; see Fig. 14-9) with another molecule of pyruvate (valine path) or with α-ketobutyrate (isoleucine path). The
α-ketobutyrate is derived from threonine in a reaction that requires pyridoxal phosphate. An intermediate in the valine
pathway, a-ketoisovalerate, is the starting point for a four-step branch pathway leading to leucine.
Three Nonessential and Six Essential Amino Acids are Synthesized from Oxaloacetate
and Pyruvate (Oxaloacetate and Pyruvate family )

6. Phosphoenolpyruvate and erythrose 4-phosphate family
Phosphoenolpyruvate
+
erythrose 4-phosphate
Chorismate
Tryptophan Tyrosine Phenylalanine
Chorismate is the common
branchpoint for the
biosyntheses of carbocyclic
aromatic compounds.