Proteins

• Amino acids are the monomers from which

  proteins are made
• Amino acids contain an amino

  group – NH2, carboxylic acid group and a variable R group which is a carbon-containing chain.

  
• There are 20 different amino acids with different R groups.
• Amino acids are joined by peptide bonds formed in condensation reactions
• A dipeptide contains two amino acids and polypeptides contain three or more amino acids.

  
• What is the structure of proteins determined by?

  The order and number of amino acids, bonding present and the shape of the protein.
• Primary structure of a protein is the order and number of amino acids in a protein.
• The secondary structure is the shape that the chain of amino acids takes – either

  alpha helix or beta pleated sheet. The shape is determined by the hydrogen

  bonding.
• Tertiary structure of proteins is the 3D shape of the protein. It can be globular or fibrous.
• Globular proteins such as enzymes are compact whereas fibrous proteins such as keratin are long and thus can be used to form fibres.
• For instance, collagen is a fibrous protein of great strength due to presence of both hydrogen and covalent bonds in the structure
• Collagen molecules wrap around each other and form fibrils which form strong collagen fibres.
• Collagen forms the structure

  of bones, cartilage and connective tissue and is a main component of tendons which connect muscles to bones.
• Haemoglobin is a water soluble globular protein which consists of two alpha and two beta polypeptide chains each containing a haem group
• It carries oxygen in the blood as oxygen can bind to the haem (Fe2+ ) group and oxygen is then released when required.