Amino Acids

• All amino acids have an Amino group(-NH_2) and a Carboxyl group(-COOM), but the R-group differs from one amino acid to another (20 R-groups and 20 amino acids)
• Amino acids have slightly different properties, as r-groups can be either: hydrophilic/polar or hydrophobic/non-polar, acidic or basic
• General Formula: NH_2RCHCOOH

  A) Variable

  B) Carboxylic (acid) groups

  C) Amine Groups

  
• The amino group acquires a hydrogen ion, so now positively charged, NH_3^+, dissolves in water as the carboxyl group dissociates,freeing a hydrogen ion (so now negatively charged, COO^-)
• Amino acids are amphoteric as they act as both acids and bases; amino acid ion has both a positive and a negative end, known as a dipolar ion or a zwitterion (property of amino acids in solution makes them pH buffers)
• Carboxyl ion can take up H^+ions from solutions (prevents it becoming acidic), and the amino ion can readily release H^+ions into solutions, neutralise OH^- ions (reduces alkalinity)
• Example: Glycine (R-group =H)

  Simplest amino acid

  
• Example: Cysteine (R-group = CH_2 - SH