Amino Acids Overview

Amino Acids

• Amino acids are organic molecules that are the building blocks of proteins.
• Approximately 300 amino acids exist naturally, but only 20 are used in protein synthesis.
• Amino acids comprise four different groups attached to a central carbon atom: an amino group, a carboxyl group, a hydrogen atom, and a side chain (R group).
• The R group distinguishes one amino acid from another, giving each unique properties.
• There are twenty different naturally occurring amino acids.

Amino Acid Classification

• Amino acids are categorized into groups based on their side chains' properties.

• Neutral amino acids: This is the largest group, further divided into:

  • Aliphatic amino acids (e.g., glycine, valine, alanine, leucine, isoleucine)
  • Aromatic amino acids (e.g., tyrosine, phenylalanine)
  • Heterocyclic amino acids (e.g., tryptophan, histidine)
  • Sulfur-containing amino acids (e.g., cysteine, methionine)

• Acidic amino acids: (e.g., aspartic acid, glutamic acid)

• Basic amino acids: (e.g., lysine, arginine)

• Polar amino acids: are classified based on polarity of side chain (R):

• OH group: serine, threonine, tyrosine

• SH group: cysteine

• amide group: glutamine and asparagine;

• NH2 group or nitrogen act as a base (basic amino acids): lysine, arginine, histidine

• COOH group (acidic amino acids): aspartic and glutamic

Essential and Nonessential Amino Acids

• Essential amino acids: cannot be synthesized by the body and must be obtained from the diet.

  • There are nine essential amino acids: phenylalanine, valine, tryptophan, threonine, isoleucine, methionine, histidine, leucine, and lysine.

• Nonessential amino acids: can be synthesized by the body.

  • There are eleven nonessential amino acids: alanine, arginine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine.

Functions of Amino Acids

• Beyond protein synthesis, amino acids have other roles:
  • Some amino acids are converted to carbohydrates (glucogenic amino acids).
  • Certain amino acids produce specialized products, including hormones (e.g., tyrosine forms thyroid hormones, epinephrine, and norepinephrine; tryptophan synthesizes niacin).
  • Amino acids like glycine, arginine, and methionine synthesize creatine.
  • Glycine and cysteine help in bile salt synthesis.
  • Glutamate, cysteine, and glycine synthesize glutathione.
  • Histidine converts to histamine through decarboxylation.
  • Serotonin is formed from tryptophan.
  • Glycine is used for heme synthesis.