Amino acid synthesis

Amino_acid_synthesis

• 
  Amino acid biosynthesis pathways
• 
  Amino acid synthesis: α-ketoglutarate family
• 
  Amino acid synthesis: erythrose-4-phosphate family
• 
  Amino acid synthesis: oxaloacetate family
• 
  Asparagine biosynthesis
• 
  Amino acid synthesis: ribose-5-phosphate family
• 
  Amino acid synthesis: 3-phosphoglycerate family
• 
  Amino acid synthesis: pyruvate family

Amino Acid Synthesis

Amino acid synthesis is the set of biochemical processes by which living organisms produce amino acids, the building blocks of proteins. These processes are essential for life, as amino acids are required for the synthesis of proteins, which perform a vast array of functions within organisms, including catalyzing metabolic reactions, DNA replication, responding to stimuli, and transporting molecules.

Overview

Amino acids are classified into two categories: essential amino acids and non-essential amino acids. Essential amino acids cannot be synthesized de novo by the organism and must be obtained from the diet. Non-essential amino acids, on the other hand, can be synthesized by the organism.

The synthesis of amino acids involves several metabolic pathways, which vary depending on the organism and the specific amino acid being synthesized. These pathways are often interconnected with other metabolic processes, such as the citric acid cycle and glycolysis.

Pathways of Synthesis

Glutamate Family

The glutamate family of amino acids includes glutamate, glutamine, proline, and arginine. These amino acids are derived from the precursor _-ketoglutarate, an intermediate in the citric acid cycle.

• Glutamate is synthesized by the reductive amination of _-ketoglutarate, catalyzed by the enzyme glutamate dehydrogenase.
• Glutamine is formed from glutamate by the enzyme glutamine synthetase, which adds an amino group to glutamate.
• Proline is synthesized from glutamate through a series of reactions involving the reduction of glutamate to glutamate-5-semialdehyde, which cyclizes to form proline.
• Arginine is synthesized from glutamate via the urea cycle, which involves the conversion of glutamate to ornithine, and then to arginine.

Aspartate Family

The aspartate family includes aspartate, asparagine, lysine, methionine, and threonine. These amino acids are derived from the precursor oxaloacetate.

• Aspartate is formed by the transamination of oxaloacetate, catalyzed by aspartate transaminase.
• Asparagine is synthesized from aspartate by the enzyme asparagine synthetase, which transfers an amino group to aspartate.
• Lysine, methionine, and threonine are synthesized through more complex pathways involving multiple steps and intermediates.

Serine Family

The serine family includes serine, glycine, and cysteine. These amino acids are derived from the precursor 3-phosphoglycerate, an intermediate in glycolysis.

• Serine is synthesized from 3-phosphoglycerate through a series of reactions involving oxidation, transamination, and dephosphorylation.
• Glycine is formed from serine by the enzyme serine hydroxymethyltransferase, which removes a hydroxymethyl group from serine.
• Cysteine is synthesized from serine through the incorporation of sulfur, which is derived from homocysteine.

Aromatic Family

The aromatic family includes phenylalanine, tyrosine, and tryptophan. These amino acids are derived from the precursor chorismate, which is formed from the shikimate pathway.

• Phenylalanine and tyrosine are synthesized from chorismate through a series of reactions involving the conversion of chorismate to prephenate, and then to phenylalanine or tyrosine.
• Tryptophan is synthesized from chorismate through a more complex pathway involving several intermediates, including anthranilate.

Regulation of Synthesis

Amino acid synthesis is tightly regulated to ensure that the cell maintains appropriate levels of each amino acid. This regulation is achieved through feedback inhibition, where the end product of a pathway inhibits the activity of an enzyme involved in its synthesis. Additionally, gene expression of enzymes involved in amino acid synthesis can be regulated in response to the availability of amino acids.

Related Pages

• Protein biosynthesis
• Metabolism
• Enzyme
• Biochemistry