Carbohydrates

• Monosaccharides have the general formula Cn(H2O)n
• What is a monosaccharide?


  A monomer made of one sugar molecule
• What do monosaccharide chains form?

  Polysaccharides
• What is a disaccharide?


  A disaccharide is a type of carbohydrate composed of two monosaccharide units joined together by a glycosidic bond.
• What are three examples of a disaccharide?


  Maltose, Sucrose, Lactose
• How do monosaccharides join together?

  In a condensation reaction, which forms a glycosidic bond.
• What is a polysaccharide?

  A polymer made up of many monosaccharides joined together
• Three main polysaccharides?


  Starch, Glycogen, Cellulose
• What is the structure of starch?

  Starch is a polysaccharide composed of alpha glucose units linked together in a linear chain (amylose) or branched chains (amylopectin).
• What is the function of starch?

  Energy storage
• How does starch's structure help its function?

  It is insoluble and so not affected by osmosis, and it is highly compact to allow for lots of sugar storage.
• What is the structure of glycogen?

  Glycogen is a branched polymer of alpha glucose molecules linked together by alpha-1,4-glycosidic bonds with alpha-1,6-glycosidic bonds at the branch points.
• How does the structure of glycogen help its function?

  Branching structure allows for rapid synthesis and breakdown of glucose molecules, providing quick energy storage and release.
• What is the structure of Cellulose?

  Beta glucose units help together by 1-4 glycosidic bonds. It has long and unbranched chains.
• What is the function of cellulose?

  The function of cellulose is to provide structural support in plant cell walls.
• How does the structure of cellulose helps is function?

  As the B-glucose units have to flip, the chain is unbranched as so has good strength in a cell wall.
• How is starch digested?

  1. Starch hydrolysed into maltose by salivary and pancreatic amylase.
  2. Maltose is hydrolysed into glucose by maltase in intestinal juice.
• How is glycogen digested?

  Hydrolysed into glucose by B-cells in the islets of Langerhans which secrete glucagon, which activates enzymes for hydrolysis.
• How is cellulose digested?


  Herbivores only (humans cannot digests and so don't have cellulose) have bacteria's in their digestive system that break it down

  Known as cellulase.
• Test for Starch?


  Add 2-3 drops of iodine

  Blue/Black precipitate formed if positive.
• Test for reducing sugars?

  Add Benedict's to the sample, mix and heat to 70 degreed Celsius in a water bath. Positive result is blue, green, yellow, orange or brick red precip.
• Test for non reducing sugars?

  Add dilute HCl, boil, cool and add NaOH to neutralise, then add benedict's, heat in water bath, and a positive result will show a brick red precipitate.
• What is a glycaemic index?


  Measure of how quickly a food raises blood sugar levels.