Proteins

• Amino acids are the monomers from which proteins are made.
• The general structure of an amino acid:

  A) Side Chain

  B) Amino group

  C) Carboxyl group

  
• A dipeptide is formed through a condensation reaction between two amino acids, releasing a water molecule and forming a peptide bond.
• bond within a single chain of amino acid is a peptide bond
• A polypeptide is formed through a condensation reaction between many amino acids, releasing a water molecule and forming a peptide bond.
• The primary structure of a protein is the sequence of amino acids in its polypeptide chains including a peptide bond
• The secondary structure of a protein involves the folding of a polypeptide chain into an alpha helix or a beta pleated sheet
• Hydrogen bonds are found in the secondary structure of a protein
• Which type of bonding is present in the tertiary structure of a protein?

  • Hydrogen
  • disulfide
  • ionic
• The amino acids in two proteins are the same, but sequenced differently. Explain why this might cause a change to the tertiary structure of the protein.

  The hydrogen, disulfide and ionic bonds could form in different locations. Meaning the polypeptide is pulled into a different 3D shape.
• Quaternary structure


  the shape we get when two or more polypeptide chains join together.
• 1. Globular proteins

  Globular proteins form spherical, ‘globe-like’ proteins.

  One example of a globular protein is haemoglobin, in which four polypeptide chains are joined in a quaternary structure.
• Fibrous proteins

  In contrast to globular proteins, fibrous proteins form long and strong fibers.

  One example of a fibrous protein is collagen.
• Describe protein structure including bonds

  1. Polymer of amino acids
  2. Joined by peptide bonds
  3. Formed by condensation reaction
  4. primary structure is order of amino acid
  5. Secondary structure is folding of polypeptide chain due to hydrogen bonding (alpha helix/pleated sheet)
  6. Tertiary structure is 3-D folding due to hydrogen bonding and ionic / disulfide bonds
  7. Quaternary structure is two or more polypeptide chains
• Test for proteins

  1. Add food sample
  2. add equal volume of sodium hydroxide
  3. add few drops of copper sulfate
  4. add biurets solution
  5. blue to purple