Arang

• Amino acids


  Organic compounds containing amine [-NH2], carboxyl [-COOH], and side chain [R group]

  
• Amino acids


  • Major key elements are carbon, hydrogen, nitrogen, oxygen
  • About 500 amino acids are known (though only 20 appear in the genetic code)
  • Can be classified in many ways

  
• Classification of amino acids

  • Gives the grouping between 20 acids and a basic outline for grouping
  • Useful for biochemists for easy understanding between each amino acid

  
• Classification based on


  • R group
  • Polarity and R group
  • Distribution in protein
  • Nutritional requirements
  • Number of amino and carboxylic groups

  
• Simple amino acids


  • Have no functional group in their side chain
  • Examples: glycine, valine, alanine, leucine, isoleucine

  
• Hydroxy amino acids


  • Have a hydroxyl group in their side chain
  • Examples: serine, threonine

  
• Sulfur containing amino acids

  • Have sulfur in their side chain
  • Examples: cysteine, methionine

  
• Aromatic amino acids


  • Have benzene ring in their side chain
  • Examples: phenylalanine, tyrosine

  
• Heterocyclic amino acids


  • Have a side chain ring which possess at least one atom other than carbon
  • Examples: Tryptophan, histidine, proline

  
• Amine group containing amino acids

  • Derivatives of amino acids in which one of carboxyl group has been transformed into an amide group
  • Examples: Asparagine, glutamine

  
• Branched chain amino acids

  • Amino acids having aliphatic side-chains with a branch
  • Examples: leucine, isoleucine, valine

  
• Acidic amino acids


  • Have carboxyl group in their side chain
  • Examples: Aspartic and Glutamic acid

  
• Basic amino acids


  • Contain amino group in their side chain
  • Examples: Lysine, Arginine

  
• Imino acid


  • Amino acids containing a secondary amine group
  • Example: Proline
• Amino acids with non polar R group

  • Hydrocarbons in nature, hydrophobic, have aliphatic and aromatic groups
  • Examples: Alanine, Valine, Leucine, Isoleucine, Proline, Phenylalanine, Tryptophan, Methionine

  
• Amino acids with polar but uncharged R Group


  • Polar and possess neutral pH value
  • Examples: Glycine, Serine, Threonine, Cysteine, Tyrosine, Glutamine, Asparagine

  
• Negatively charged amino acids

  • Their side chain [R Group] contain extra carboxyl group with a dissociable proton
  • Renders electrochemical behaviour to proteins
  • Examples: Aspartic acid and Glutamic acid

  
• Positively charged amino acid


  • Their side chain have extra amino group
  • Rendering basic nature to protein
  • Examples: Lysine, Arginine, Histidine

  
• Standard protein amino acids

  • The amino acids that are used to form proteins, recognized by ribozyme autoaminoacylation systems
  • Examples: Histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

  
• Non standard protein amino acids

  • These amino acids are not required to build proteins, have a vital role as metabolic intermediates
  • Examples: Hydroxyproline, Hydroxylysine, Carboxyglutamate, Diaminopimelate

  
• Non standard non protein amino acid


  • These are the derivative of amino acids and have role in metabolism
  • Examples: Alpha amino butyrate, Citruline, Ornithine, beta-alanine

  
• Essential amino acids


  • Cannot be made by the body, must come from food
  • Examples: Arginine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine

  
• Non essential amino acids


  • Can be made by humans and so is essential to the human diet
  • Examples: Alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine, and tyrosine

  
• Monoamino- monocarboxylic amino acids


  • Examples: glycine, alanine, proline, phenylalanine, methionine, serine, threonine

  
• Monoamino-dicarboxyli amino acid


  • Examples: Aspartic and glutamic acid

  
• Diamino-monocarboxylic amino acids


  • Examples: Lysine, arginine, histidine

  
• Physical properties of amino acids

  • Colourless, crystalline, tasteless/sweet, melting point above 200°C, soluble in polar solvent and insoluble in non polar solvent, have absorbance at 280nm, molecular weight 100 - 50,000 Daltons, possess optical isomers, some are structurally stable and sterically hindered, possess enzymatic activities, exhibit colloidal nature and denaturing property
• Decarboxylation


  1. Amino acids undergo decarboxylation to form the corresponding "amines"

  2. Examples: Histidine → Histamine + CO2, Tyrosine → Tyramine + CO2, Lysine → Cadaverine + CO2

  
• Reaction with Alkalies (Salt formation)


  The carboxyl group of amino acids can release a H+ ion with the formation of Carboxylate (COO–) ions

  
• Reaction with Alcohols (Esterification)

  The amino acids is reacted with alcohol to form, "Ester". The esters are volatile in contrast to the form amino acids

  
• Reaction with DANSYl Chloride


  When the amino acid reacts with DANSYl chloride reagent, it gives a "Flourescent DANSYl derivative

  
• Reaction with acylating agents (Acylation)


  When the amino acids react with "Acid chloride" and acid anhydride in alkaline medium it gives "pthaloyl amino acid

  
• Reaction with Sanger's reagent

  "1-flouro-2,4-dinitrobenzene" is called Sanger's reagent (FDNB). Sanger's reagent reacts with α-amino acid to produce Yellow coloured derivative, DNB-amino acid

  
• Reaction with Edmann's reagent

  Edmann's reagent is "phenylisothiocyanate". When amino acids react with Edmann's reagent it gives "phenyl thiohydantoic acid" finally it turns into cyclized form "Phenyl thiohydantoin" (Edmann's derivative)