Amino Acid

• Amino acids


  An important part of our total diet. Proteins are broken down in the digestive process producing amino acid needed to build tissues, enzymes, skin and hair
• Amino acid structure


  They contain an amino group and a carboxylic acid group. Individual amino acids are differentiated by variations in the R group, a group of atoms attached to the central carbon atom
• Typical amino acids


  • Alanine
  • Valine
  • Leucine
  • Isoleucine
  • Proline
  • Methionine
  • Phenylalanine
  • Tryptophan
  • Glycine
  • Serine
  • Threonine
  • Cysteine
  • Tyrosine
  • Asparagine
  • Glutamine
  • Aspartic acid
  • Glutamic Acid
  • Lysine
  • Arginine
  • Histidine
• Dipeptide


  Formed when two amino acids bond together by forming a peptide bond
• Chromatography of amino acids

  1. Different amino acids move at different rates in an organic solvent as they move up a chromatography paper or a thin-layer plate

  2. Spots of the amino acids are placed near the bottom of the paper or plate

  3. The solvent travels up the paper or plate carrying the amino acids with it

  4. The amino acids separate due to their different solubilities

  5. The amino acids can be detected by spraying with ninhydrin

  6. The Rf value is calculated as the ratio of the distance traveled by the amino acid to the distance traveled by the solvent
• Aspartame can be hydrolysed to produce a dipeptide hydrolysate
• Ninhydrin reacts with amino acids to produce colored spots
• The Rf value represents the ratio of the distance traveled by the amino acid to the distance traveled by the solvent
• Identical amino acids will travel the same distance, give the same Rf values and form the same color with ninhydrin
• Amino acids


  Monomers or building blocks of proteins
• Amino acids


  • Organic molecules with carboxyl and amino groups bonded to the same carbon
  • The other 2 bonds of the carbon are to a hydrogen and R group
  • Amino acids differ in their properties due to differing side chains, called R groups
• Types of amino acids

  • Nonpolar side chains; hydrophobic
  • Polar side chains; hydrophilic
  • Electrically charged side chains; hydrophilic
• Formation of dipeptides


  1. Two amino acids bond together by forming a peptide bond

  2. Peptide bonds are formed when the amino group of one amino acid reacts with the carboxyl group of the other amino acid, forming a water molecule
• Hydrolysis of dipeptides


  Breaking of peptide bonds by the addition of water
• Paper chromatography


  • A method in separating substances using a sheet of paper (cellulose) for the stationary phase
  • Solvents (always a liquid) for the mobile
• Thin-layer chromatography


  • Same as paper chromatography but this technique uses a piece of plastic or glass coated with a thin-layer of alumina or silica gel for stationary phase
• How paper/thin-layer chromatography works

  1. Separates several spots representing different samples and standards on the same sheet

  2. Flow direction - ascending

  3. Mixture to be separated is first "spotted" (applied as a small spot using capillary tube) within 1 inch of one edge of rectangular paper sheet or TLC plate

  4. The paper sheet or TLC plate (with spots) is placed in a "developing chamber" that has the mobile phase in the bottom to a depth lower than the bottom edge of the spots

  5. The mobile phase proceeds upward by capillary action and sweeps the spots along with it

  6. The chromatogram reveals the identities of the components, especially if standards were spotted on the same paper or plate or using Rf values
• Rf value


  Retention factor, used to compare with those of standards to reveal the identities of the components
• Rf = distance traveled by mixture component / distance traveled by the solvent