3.2 Amino Acids: The Building Blocks for Proteins

• Amino Acids


  • Contain both an amino (—NH2 ) and a carboxyl (—COOH) group

  • α-amino acids: Amino acids in which the amino group and the carboxyl group are attached to the α-carbon atom
  • Side chains (R) - Vary in size, shape, charge, acidity, functional groups present, hydrogen-bonding ability, and chemical reactivity
  • more than 700 amino acids are known
• The general structural formula for an a-amino acid

  A) Side chain

  B) Carboxyl group

  C) Amino group

  
• Standard Amino Acids

  • 20 α-amino acids normally found in proteins

  • Divided based on the properties of R-groups

  – Nonpolar amino acids: Contain one amino group, one carboxyl group, and a nonpolar side chain

  • Hydrophobic - Not attracted to water molecules

  • Found in the interior of proteins, where there is no polarity

  – Polar amino acids - Hydrophilic

  • Types - Polar neutral, polar acidic, and polar basic
• Polar Amino Acids

  • Polar neutral: Contain polar but neutral side chains

  – Six amino acids belong to this category

  • Polar acidic: Contain a carboxyl group as part of the side chains

  – Two amino acids belong to this category

  • Polar basic: Contain an amino group as part of the side chain

  – Three amino acids belong to this category