1.6 - Proteins

• What are amino acids ?

  The basic monomers that combine to make a polymer called a polypeptide which are combined to form proteins
• What’s the general structure of an amino acid ?


  .

  
• What does the NH2 represent ?


  amine group
• What does the COOH represent ?


  A carboxyl group
• What does the R represent ?

  R group, a side chain that’s a variety if different chemical groups
• How do the naturally occurring amino acids (20) differ ?


  Only differ in their R group
• What do amino acid monomers combine to form ?


  A dipeptide
• What bond is formed in the condensation reaction between 2 amino acids ?


  A peptide bond
• Where does the OH come from and where does the H come from when a peptide bond forms ?


  OH comes from the carboxyl group and the H comes from the amine group of another amino acid
• How is a polypeptide formed ?


  A series of condensation reactions where many amino acids join together (polymerisation)
• How many polypeptides will a protein have ?


  A functional protein may contain 1 or more polypeptides
• What’s the primary structure of a protein ?


  The sequence of amino acids in a polypeptide chain that’s determined by DNA
• What is the primary structure determined by ?


  The sequence of DNA bases
• What does the primary structure determine ?


  A proteins shape and function
• What’s the secondary structure of proteins ?


  When the polypeptide folds and twists into a 3D shape like the coil known as an alpha-helix
• Why does a secondary structure form ?


  The hydrogen has a positive charge and the oxygen has a negative charge so they readily form weak hydrogen bonds which cause the chain to twist into alpha-helix
• What’s the tertiary structure of a protein ?


  The secondary structure can be twisted even more to give a more complex, specific 3D structure
• What 3 bonds can maintain the tertiary structure ?

  Disulfide bridges, ionic bonds, hydrogen bonds
• What are disulfide bridges ?


  between sulfur atoms on the variable R groups, fairly strong so not easily broken
• What are ionic bonds ?


  Between any charged R group, easily broken by pH changes
• What are hydrogen bonds ?


  There are numerous hydrogen bonds but are easily broken
• What’s the quaternary structure ?


  The combination of a number of different polypeptide chains and associated non-protein groups into a large, complex protein molecule
• What determines the 3D structure of a protein ?


  The sequence of amino acids in the polypeptide chain
• What 2 kinds of protein can you have ?

  Globular and Fibrous
• What’s the structure of a fibrous protein ?


  Form long chains running parallel to each other that are linked by cross-bridges
• 2 properties of fibrous proteins ?


  Insoluble and physically tough
• Structure of a globular protein ?


  Many polypeptides tightly folded to make a spherical shape
• A property of globular proteins ?


  Soluble in water
• What’s the test for proteins ?

  The biuret test
• The method of the biuret test ?


  • place the sample solution in test tube and biuret reagent
  • A purple colour shows protein is present and a blue colour shows it id absent