Biological molecules : Cabohydrates
- Created by: joycelyn boateng
- Created on: 29-09-17 13:13
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- Biological Molecules: Carbohydrates
- Carbohydrates = carbon + water
- The making of large molecules
- Monomer - individual molecules that form chains
- Polymers - monomers that join together
- In carbohydrates, the basic unit is sugar (saccharide)
- Monosaccharide - A single monomer
- General Formula (CH2O)n where n can be any number from three to seven
- Examples of monosaccharides ; Glucose C6H12O6 ,Galactose and fructose
- Disaccharide - A pair of monosaccharides
- Monosaccharide - A single monomer
- Testing for non reducing sugars
- Reducing Sugars - Is a sugar that can donate electrons to (or reduce) another chemical
- Method - 1) Add 2cm3 of the food sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water. 2) Add an equal volume of benedict's reagent 3) Heat the mixture in a gently boiling water bath for five minutes 4) If reducing sugar is present solution turns orange - brown
- Colour Change - Blue = no reducing sugar present , green = very low, yellow = low, orange = medium , red = high concentration
- Disaccharides
- Glucose + Glucose = Maltose
- Glucose + Galactose = Lactose
- Condensation Reaction - When the monosaccharides join a molecule of water is removed
- Glucose + Fructose = Sucrose
- Hydrolysis - When water is added to a disaccharide under suitable conditions, it breaks down glyosidic bonds and releases the constituent monosaccharides
- Test for non reducing sugars
- 1) If the sample is not already in liquid form, it must be ground up in water.
- 2) Add 2cm3 of the food sample being tested to 2cm3 of benedicts reagent in a test tube a filter
- 3) Place the test tube in boiling water bath for five minutes. If the solution doesn't change colour that means that there is no reducing sugars present
- 4) Add another 2cm3 of the food sample to 2cm3 of dilute HCL in a test tube and place the test tube in boiling water for five mins (The dilute HCL will hydrolyse any disaccharide present into its constituent monosaccharides
- 5) Slowly add some sodium hydrogen carbonate solution to the test tube in order to neutralise the HCL ( Benedicts reagent wont work in acidic conditons ) Test the pH paper to check that the solution is alkaline
- 6) Retest the resulting solution by heating it with 2cm3of benedict's reagent in boilng water for five mins
- 7) If an non reducing sugar was present in the original sample, the benedicts reagent will now turn orange - brown . This due to the reducing sugars that were produced form the hydrolysis of non reducing sugars
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