Carbohydrates

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Carbohydrates

  1. 1. Carbohydrates
  2. 2. What are carbohydrates? <ul><li>Starter: </li></ul><ul><li>Write down as many things as you can remember about carbohydrates… </li></ul><ul><li>… or glucose in particular </li></ul>
  3. 3. What are they? <ul><li>Organic compounds which comprise of only C, H and O </li></ul><ul><li>Carbo - Hydr - ate </li></ul>
  4. 4. Types of Carbohydrate <ul><li>Monosaccharides </li></ul><ul><li>Disaccharides </li></ul><ul><li>Polysaccharides </li></ul>
  5. 5. Monosaccharides <ul><li>Simplest – ‘Single sugars’ </li></ul><ul><li>Same no. of C as O atoms </li></ul><ul><li>e.g. Glucose is C 6 H 12 O 6 </li></ul><ul><li>Have the general formula (CH 2 O) n </li></ul><ul><ul><ul><li>Where n is any number between 3 and 7 </li></ul></ul></ul><ul><li>White crystalline solids </li></ul><ul><li>Dissolve in water to form sweet tasting solutions </li></ul>
  6. 6. The structure of glucose <ul><li>α -glucose </li></ul>You only need to be able to draw α -glucose in its simplified form….
  7. 7. <ul><li>β -glucose </li></ul>The structure of glucose <ul><li>α -glucose and β -glucose are ISOMERS </li></ul>
  8. 8. Monosaccharides form Disaccharides + H 2 O Maltose
  9. 9. <ul><li>The bond formed is a glycosidic bond </li></ul><ul><li>A condensation reaction occurs to join the 2 monosaccharides </li></ul>Monosaccharides form Disaccharides <ul><li>α 1-4 glycosidic bonds </li></ul>
  10. 10. Disaccharides hydrolyse to form Monosaccharides α -glucose α -glucose H 2 O
  11. 11. Disaccharides form Polysaccharides <ul><li>Starch </li></ul>
  12. 12. Starch <ul><li>The α -helical structure of starch makes it good for storage (it’s compact!) </li></ul><ul><li>Starch is insoluble due to its structure </li></ul><ul><li>It is therefore the main plant storage sugar </li></ul>
  13. 13. Cellulose <ul><li>Polymer of β -glucose </li></ul><ul><li>Each monomer is </li></ul><ul><li>inverted. </li></ul><ul><li>Has consequences for </li></ul><ul><li>its properties </li></ul>
  14. 14. Cellulose <ul><li>Forms chains which run parallel with hydrogen bonds between the chains to form microfibrils </li></ul><ul><li>Microfibrils are strong </li></ul><ul><li>Being fibrous, cellulose is structurally important in plant cell walls </li></ul>
  15. 15. Glucose is not the only monosaccharide... <ul><li>Fructose: </li></ul>Glucose and fructose combine to form sucrose (a disaccharide)
  16. 16. Glucose is not the only monosaccharide... <ul><li>Galactose </li></ul>Glucose and galactose combine to form Lactose Galactose Glucose
  17. 17. Summary <ul><li>α -glucose + α -glucose = maltose </li></ul><ul><li>The polymer of α -glucose is starch </li></ul><ul><li>The polymer of β -glucose is cellulose </li></ul><ul><li>Glucose + fructose = sucrose </li></ul><ul><li>Glucose + galactose = lactose </li></ul>
  18. 18. <ul><li>Biochemical Test for a Monosaccharide </li></ul>
  19. 19. <ul><li>All monosaccharides and some disaccharides are Reducing Sugars </li></ul><ul><li>i.e. They readily reduce other chemicals when in solution </li></ul><ul><li>We test for reducing sugars using the Benedict’s Test </li></ul>
  20. 20. Benedicts Test <ul><li>2cm³ of food sample (in liquid form) </li></ul><ul><li>2cm³ of Benedict’s Reagent </li></ul><ul><li>Heat mixture in gentle boiling water bath for 5mins </li></ul>Conc. of reducing sugar Colour of solution & precipitate None Stays blue Very Low Green Low Yellow Medium Brown/orange High Brick red
  21. 21. <ul><li>In order to detect a reducing sugar, it must first be hydrolysed into its monosaccharide components: </li></ul><ul><ul><li>First test with Benedict’s reagent </li></ul></ul><ul><ul><li>If no colour change: </li></ul></ul><ul><ul><ul><li>Add 2cm³ of food sample to 2cm³ of dilute HCl </li></ul></ul></ul><ul><ul><ul><li>Place in gently boiling water bath for 5 mins </li></ul></ul></ul><ul><ul><ul><li>Slowly add some sodium hydrogen carbonate solution until neutralized </li></ul></ul></ul><ul><ul><ul><li>Re-test using Benedict’s reagent </li></ul></ul></ul>

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