Carbohydrates

Carbohydrates

1. Formulas

   • Monosaccharide's- (CH20)n
     • 1-Sweet tasting 2-soluble 3-atoms form a ring shape.
   • Disaccharide's- 2(CH20)n-H2O

2. Reactions

   • Condensation- Joins molecules making water.
   • Hydrolysis- Separates molecules using water.

3. Glucose- (monosaccharide.)

   • C6H12O6
   • alpha-glucose.
     • Two alpha-glucose monosaccharide's can join together to make a disaccharide.
       • alpha-glucose + alpha-glucose: maltose + water.
         • Can also go backwards in a hydrolysis reaction to form two alpha-glucose molecules from maltose and water.
       • Forms a glycosidic bond when the hydroxide group and oxygen are removed to form a COC bond.
   • beta-glucose.

4. Disaccharides

   • Sucrose
     • Made from glucose and fructose.
   • Maltose
     • Made from two glucose molecules.
   • Lactose
     • Made from galactose and glucose.

5. Tests for sugars.

   • Reducing sugars.
     • All monosaccharide's and some disaccharides are reducing sugars.
     • Benedict's Test
       • 1- Add sample to a test tube. 2- Add ten drops of benedicts reagent. 3- Heat to 90 degrees in a water baths. 4- Observe a colour change.
       • If reducing sugars are present then it will change colour to a red/brown. Depending on its concentration it may even turn green, indicating there is a very low concentration.
   • Non-reducing sugars.
     • This test is more complicated as the sugars, if present first have to be broken down by acid hydrolysis to produce the reducing sugars like monosaccharide's and some disaccharides.
     • 1- Add sample to a test tube. 2- Add HCl and heat in a water bath (acid hydrolysis). 3- Leave to cool and add sodium hydrogencarbonate powder to make to solution neutral. 4- Add ten drops of benedicts reagent and observe a colour change.
     • If non-reducing sugars are present then the colour will change as above.
     • This test should only be completed once there is a negative result for reducing sugars.

6. Polysaccharides.

   • Starch.
     • Test for starch is to add iodine. If starch is present it will turn brown/black, depending on concentration.
     • Made of alpha-glucose; they're unbranched.
     • They're a good energy store and respiratory substrate found in grains in potato tubers, seeds and stoma of chloroplasts.
     • Properties: Compact, too big to pass through membranes, insoluble- osmotically inactive, many glucose molecules, arranged in a helix.
   • Glycogen
     • Made of alpha-glucose and found in humans in the liver and muscles. Also found in fungi and bacteria.
     • They're branched and act as a quick energy release stores and regulate blood glucose levels.
     • Properties: branched, insoluble and tightly coiled.
   • Cellulose.
     • Properties: Mechanically strong, inverted arrangement of successive glucose molecules forming hydrogen bonds, tightly crossed-linked to form micro fibrils and fibres, interwoven, gaps allow permeability.
     • Made of beta-glucose; they're unbranched.
     • They're good at maintaining cell wall turgidity- leaves held in place and stem flexible but firm in the wind.

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