Proteins

• Elements in proteins


  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrogen
  • Sulfur
  • Phosphorus
• Proteins contain the elements carbon, hydrogen, oxygen and nitrogen. They sometimes contain smaller amounts of sulfur and some may contain phosphorus and other elements.
• There is no ratio for the elements in a protein, but proteins are very large and complex, often containing tens of thousands of atoms.
• Peptide


  A small number of amino acids (less than 20) joined by peptide bonds
• Proteins


  • A long polypeptide (at least 200 amino acids)
  • Amino acids that make up a protein can be thought of as the letters in an alphabet
  • By combining them in different sequences, nature can make a huge range of proteins
• Amino acids


  The building blocks of proteins
• Polypeptide


  More than 20 amino acids joined by peptide bonds
• The way in which a protein works does not depend on the amino acid sequence alone. The manner in which the proteins are folded to take up three-dimensional (3-D) shapes is equally important.
• Prions are proteins that do not fold correctly. They cause similar proteins to fold incorrectly and are responsible for brain and nervous system diseases such as bovine spongiform encephalopathy (BSE in cattle), Creutzfeldt-Jakob disease (CJD; in humans) and scrapie (in sheep).
• Fibrous proteins


  • Show little or no folding
  • Form long fibres
  • Are strong and tough, e.g. keratin in hair, nails and feathers
• Globular proteins


  • Show lots of folding
  • Form rounded shapes, e.g. in egg white (albumen) and enzymes
• Sources of protein


  • Meat
  • Fish
  • Eggs
  • Nuts
  • Milk
  • Peas and beans
• Amino acids are not stored in the body. Surplus amino acids are taken to the liver and converted into urea, which is a toxic waste product.
• Deamination


  1. Surplus amino acids are taken to the liver

  2. Converted into urea

  3. Urea is carried by the blood from the liver to the kidneys

  4. In the kidneys, urea becomes part of urine and is excreted
• Proteins


  Composed of amino acids
• Number of common amino acids found in proteins

  • 20
• Proteins have a variety of structures
• Fibrous protein


  • Keratin is found in skin and hair
  • Myosin is found in muscle
• Metabolic role of proteins

  • Proteins are used as enzymes to control reactions
  • They form antibodies to fight infection
  • Some hormones are protein-based and are used to regulate body reactions