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Carbohydrates

Carbohydrates. What are carbohydrates?. Starter: Write down as many things as you can remember about carbohydrates… … or glucose in particular. What are they?. Organic compounds which comprise of only C, H and O Carbo - Hydr - ate. Types of Carbohydrate. Monosaccharides Disaccharides

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Carbohydrates

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  1. Carbohydrates

  2. What are carbohydrates? Starter: Write down as many things as you can remember about carbohydrates… … or glucose in particular

  3. What are they? • Organic compounds which comprise of only C, H and O • Carbo-Hydr-ate

  4. Types of Carbohydrate • Monosaccharides • Disaccharides • Polysaccharides

  5. Monosaccharides • Simplest – ‘Single sugars’ • Same no. of C as O atoms e.g. Glucose is C6H12O6 • Have the general formula (CH2O)n Where n is any number between 3 and 7 • White crystalline solids • Dissolve in water to form sweet tasting solutions

  6. The structure of glucose • α-glucose You only need to be able to draw α-glucose in its simplified form….

  7. The structure of glucose • β-glucose • α-glucose and β-glucose are ISOMERS

  8. Monosaccharides form Disaccharides + Maltose H2O

  9. Monosaccharides form Disaccharides • The bond formed is a glycosidic bond • A condensation reaction occurs to join the 2 monosaccharides • α 1-4 glycosidic bonds

  10. Disaccharides hydrolyse to form Monosaccharides H2O α-glucose α-glucose

  11. Disaccharides form Polysaccharides Starch

  12. Starch • The α-helical structure of starch makes it good for storage (it’s compact!) • Starch is insoluble due to its structure • It is therefore the main plant storage sugar

  13. Cellulose • Polymer of β-glucose • Each monomer is inverted. • Has consequences for its properties

  14. Cellulose • Forms chains which run parallel with hydrogen bonds between the chains to form microfibrils • Microfibrils are strong • Being fibrous, cellulose is structurally important in plant cell walls

  15. Glucose is not the only monosaccharide... • Fructose: Glucose and fructose combine to form sucrose (a disaccharide)

  16. Glucose is not the only monosaccharide... • Galactose Glucose and galactose combine to form Lactose Galactose Glucose

  17. Summary • α-glucose + α-glucose = maltose • The polymer of α-glucose is starch • The polymer of β-glucose is cellulose • Glucose + fructose = sucrose • Glucose + galactose = lactose

  18. Biochemical Test for a Monosaccharide

  19. All monosaccharides and some disaccharides are Reducing Sugars i.e. They readily reduce other chemicals when in solution • We test for reducing sugars using the Benedict’s Test

  20. Benedicts Test • 2cm³ of food sample (in liquid form) • 2cm³ of Benedict’s Reagent • Heat mixture in gentle boiling water bath for 5mins

  21. In order to detect a reducing sugar, it must first be hydrolysed into its monosaccharide components: • First test with Benedict’s reagent • If no colour change: • Add 2cm³ of food sample to 2cm³ of dilute HCl • Place in gently boiling water bath for 5 mins • Slowly add some sodium hydrogen carbonate solution until neutralized • Re-test using Benedict’s reagent

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