Carbohydrates

• Define a monosaccharide

  a carbohydrate monomer
• Define a disaccharide

  Two monosaccharides joined by a glycosidic bond in a condensation reaction
• What is the biochemical test for reducing sugars?

  -Add Benedict's Reagent

  -Heat the solution

  -A brick red precipitate forms in a positive test
• What is the biochemical test for non reducing sugars?

  -Carry out the test for reducing sugar to make sure it is negative

  -Boil with dilute acid to break glycosidic bonds

  -Neutralise with dilute alkali

  -Add Benedict's Reagent

  -Heat the solution

  -A brick red precipitate forms in a positive test
• Describe the structure of starch

  A polysaccharide of alpha glucose

  Made from amylose and amylopectin

  Stored in starch granules and amyoplasts
• What is the biochemical test for starch?

  -Add potassium iodide solution

  -A blue-black colour change occurs in a positive test
• Describe the structure of glycogen

  A polysaccharide of alpha glucose

  Branched chains with 1-4, and 1-6 glycosidic bonds

  Stored in liver and muscle tissue
• What are 4 reasons why glycogen and starch are effective storage molecules?

  -Helical, so compact

  -Highly branched so quickly hydrolysed to glucose for respiration

  -Insoluble in water so no osmotic damage

  -Too large to cross cell membranes so cannot leave cells
• Describe the structure of cellulose

  A polysaccharide of beta glucose

  Made of 1-4 glycosidic bonds

  Alternate beta glucoses are flipped

  Makes plant cell walls
• What are 3 reasons why cellulose is effective at making plant cell walls?

  -Made of long, straight, unbranched chains

  -Parallel chains linked by H bonds, making microfibrils

  -Microfibrils provide strength and rigidity