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  1. 1. Proteins.
  2. 2. Function of proteins. <ul><li>Proteins are very important in living organisms and take on a variety of forms and functions: </li></ul><ul><li>Enzymes. </li></ul><ul><li>Antibodies. </li></ul><ul><li>Actin and myosin </li></ul><ul><li>Collagen. </li></ul><ul><li>Keratin </li></ul><ul><li>antigens </li></ul>
  3. 3. The structure of proteins. <ul><li>Proteins are made up of carbon, hydrogen, oxygen and nitrogen. Sometimes sulphur is present. </li></ul><ul><li>Proteins are polymers made up of the monomers called amino acids. </li></ul><ul><li>There are 20 different amino acids. </li></ul><ul><li>Amino acids can join up in any order and form an infinite number of protein molecules. </li></ul>
  4. 4. Amino acids. <ul><li>Amino acids contain an amino group (-NH ²) and a carboxylic acid group (-COOH). </li></ul><ul><li>Each amino acid has an R group. </li></ul><ul><li>There are 20 different R groups and this is the reason for there being 20 different types of amino acids. </li></ul>
  5. 5. Structure of an amino acid. Carboxylic acid group Amino group R Group
  6. 6. How do two amino acids join together ? <ul><li>Two amino acids join together by condensation to form a dipeptide . </li></ul>A peptide bond is formed and this results in a dipeptide
  7. 7. What is a polypeptide? <ul><li>A chain of amino acids is known as a polypeptide. </li></ul>
  8. 9. Proteins can be divided into groups. <ul><li>Globular proteins. These are molecules that are often spherical in shape and have a chemical function eg enzymes. </li></ul><ul><li>Fibrous proteins . These have a structural role . They give strength or elasticity to a particular tissue eg keratin in hair. </li></ul>
  9. 10. Four levels of structure. <ul><li>Primary structure. A sequence of amino acids in a polypeptide chain. </li></ul><ul><li>Secondary structure. The chain of amino acids bend and twist and forms a stable structure that is held in position by hydrogen bonds. A helix is the most common secondary structure. </li></ul>
  10. 12. <ul><li>Tertiary structure. The secondary structure folds to give a more three dimensional shape. The shape is maintain by hydrogen bonds and the stronger disulphide bridges which form between the sulphur containing amino acids molecules. </li></ul><ul><li>Such proteins are often called globular proteins. their shape is vital to their function. Eg enzymes. </li></ul>
  11. 15. <ul><li>Quaternary structure- the protein consists of more than one polypeptide. The different polypeptide chains bind together to form a whole molecule. Eg insulin is made up of two polypeptide chains whilst haemoglobin is made up of four. </li></ul>
  12. 16. Haemoglobin is made up of 4 different polypeptide chains. Keratin is a secondary structure protein. it has a spiral shape and is held in position by hydrogen bonds. Haem group Haemoglobin molecule
  13. 17. Globular proteins. <ul><li>Globular proteins have the following characteristics: </li></ul><ul><li>Irregular amino acid sequence </li></ul><ul><li>Sequence is highly specific and never varies between 2 examples of the same protein. </li></ul><ul><li>Polypeptides fold into a spherical shape. </li></ul><ul><li>Relatively unstable structure. </li></ul><ul><li>Metabolic functions. </li></ul><ul><li>Egs enzymes, hormones and haemoglobin. </li></ul>
  14. 18. Enzymes.
  15. 19. Structure and function of globular proteins. <ul><li>The shape of a globular protein is very delicate and vital to it’s function. </li></ul><ul><li>An enzyme has a precise tertiary structure that provides it with it’s active site. Any change in the shape of the active site will stop the enzyme from working. </li></ul><ul><li>High temperatures make the molecules vibrate and this causes the weak hydrogen bonds to break and as a result the shape changes. The enzyme is denatured and will not work. </li></ul>
  16. 20. Denaturation of proteins. <ul><li>The three dimensional shape of proteins is maintained by hydrogen bonds and ionic bonds which are fairly weak. </li></ul><ul><li>Any agent such as heat, acids or alkalis will break these bonds and cause a change in shape. </li></ul><ul><li>With a change in shape the protein can no longer carry out it’s function. </li></ul>
  17. 21. Questions. <ul><li>1 Describe the general structure of an amino acid. </li></ul><ul><li>2 With the aid of a diagram , show the results when two amino acids are joined together. </li></ul><ul><li>3 Proteins may be described as having: </li></ul><ul><li>4 Primary, secondary, tertiary or quaternary structures. Explain the meanings of these terms when applied to proteins. </li></ul>
  18. 22. <ul><li>5 Describe the characteristics of a globular protein. </li></ul><ul><li>6 How is the structure of a globular protein related to it’s function? </li></ul><ul><li>7 What is meant by the term denatured? </li></ul><ul><li>8 Explain how a protein may become denatured. </li></ul>