Amino acids are classified into essential, non-essential, and semi-essential types based on their ability to be synthesized by the human body. Essential amino acids must be obtained through diet, while non-essential can be made by the body, and semi-essential are needed in childhood. The biosynthesis of amino acids involves metabolic pathways like glycolysis and the Krebs cycle, with amination and transamination processes facilitating their formation.

1. BIOSYNTHESIS OF AMINO
ACIDS
S. Nahidha Begum
II. M.Sc Microbiology
Sacred Heart College

2. BIOSYNTHESIS OF AMINO ACIDS
Amino acids are organic compounds that contain both an amine group
(-NH ) and a carboxyl group (-COOH), along with a distinctive side chain
₂
Nutritional Classification of Amino Acids
Nutritionally Amino acids are classified into three types. They are
• Essential Amino acids
• Non-essential Amino acids
• Semi-essential Amino acids

3. 1. Essential Amino Acids (Indispensable Amino Acids):
• These amino acids cannot be synthesized by the human body and must be obtained through diet.
• List of Essential Amino Acids:
 Valine
 Isoleucine
 Leucine
 Lysine
 Methionine
 Phenylalanine
 Threonine
 Tryptophan
• The importance of these amino acids in the diet was first described by William Cumming Rose.

4. 2. Non-Essential Amino Acids (Dispensable Amino Acids):
• These amino acids can be synthesized by the human body and are not required in the
diet.
• List of Non-Essential Amino Acids:
 Glycine
 Alanine
 Serine
 Cysteine
 Aspartate
 Asparagine
 Glutamate
 Glutamine
 Tyrosine
 Proline

5. 3. Semi-Essential Amino Acids:
• These amino acids are synthesized by adults but not sufficiently by
growing children and thus are required in the diet for children.
• List of Semi-Essential Amino Acids:
 Arginine
 Histidine

6. Biosynthesis of Amino Acids
• Amino acids are crucial for protein biosynthesis.
• Certain microorganisms, like Escherichia coli, have the enzymes needed to synthesize all
amino acids using basic starting materials such as glucose and inorganic salts.
• Organisms capable of synthesizing amino acids can do so either directly or indirectly from
intermediates of carbohydrate metabolism.
• All amino acids are derived from intermediates in key metabolic pathways: Glycolysis, the
Citric Acid Cycle (Krebs Cycle), or the Pentose Phosphate Pathway.
• The Krebs Cycle is a significant source of intermediates (precursors) for amino acid
synthesis. The process of converting an acid to an amino acid by adding an amine group is
known as amination.
• When the amine group is derived from an existing amino acid, the process is called
transamination.

7. Biosynthesis of Amino acids

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