Amino acids

Amino acids are the monomer of protein containing both amino group and carboxyl group.

Structure of amino acids:

Each amino acid has an α-amino group (- NH3+), an α-carboxyl group (- COOH), and a distinctive side chain (R- group) attached to the α-carbon atom.

Types of amino acids:

20 amino acids are necessary for human body. Of these, some can be produced by the liver – called non essential amino acids; the rest must be supplied by food – called essential amino acids.

According to nutritional value, amino acids may be classified as:

Essential amino acids – Amino acids that cannot be produced by the body but essential for growth and development of body. These amino acids must be obtained from diet. Protein containing diet including milk, egg, meat, and cheese contain all essential amino acids but grains and vegetables do not contain all the essential amino acids.

Non essential amino acids – These amino acids that can be produced by the body.

List of 20 Amino acids:

8 are essential amino acids12 are non essential amino acids
IsoleucineAlanine
TryptophanAsparagine
PhenylalanineAspartate
MethionineCysteine
ThreonineGlutamate
LysineGlycine
LeucineProline
ValineGlutamine
Serine
Tyrosine
Arginine *
Histidine*

*Argnine and histidine are essential under specific condition.

According to the nature of their catabolic end products,  amino acids may be classified as:

Glucogenic amino acids – Amino acids whose catabolism generates pyruvate or one of the intermediates of citric acid cycle are called glucogenic or glycogenic amino acids. These intermediates can give rise to formation of glucose or glycogen in liver and glycogen in skeletal muscle by the process of gluconeogenesis.

Ketogenic amino acids – Amino acids whose catabolism generates either acetoacetate or one of its precursor (acetyl CoA or acetoacetyl CoA) are called ketogenic amino acids. Acetoacetate is one of the ketone bodies.

List of ketogenic and glucogenic amino acids:

KetogenicGlucogenic and ketogenic Glucogenic
LysineTyrosineAlanine
LeucineIsoleucineAsparagine
TryptophanAspartate
PhenylalanineCysteine
Glutamate
Glutamine
Glycine
Proline
Serine
Methionine
Threonine
Arginine
Histidine
Valine

Branched chain amino acids:

The essential amino acids valine, isoleucine, and leucine are called branched chain amino acids. Branched chain amino acid refers to their chemical structure. Therapeutically, these amino acids are valuable because they pass through the liver in unchanged form and are available for cellular uptake from circulation, preferentially metabolized in muscle. Parenteral administration of branched chain amino acids is beneficial whenever catabolism due to physiological stress occurs. The skeletal muscle can be used these amino acids for energy.

Amino acids benefits:

  • Amino acids act as the building blocks of our body proteins.
  • Some amino acids participate in transmission of impulse in the nervous system.
  • These are the precuesors of hormone, purines, pyrimidines, and some vitamins like pantothenic acid ( vitamin B3) and folic acid.
  • Essential amino acids support infant growth and maintain health in adult.

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