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.
• Structure of proteins is 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.