MSacs, DSacs,PSacs

Note by hannah.lindridge, updated more than 1 year ago
Created by hannah.lindridge about 8 years ago


A-Levels Biology (Enzymes and the digestive system) Note on MSacs, DSacs,PSacs, created by hannah.lindridge on 05/14/2013.

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MonosaccharidesMany organic molecules made up of chains of individual molecules (monomers)Longer chains of repeating monomers=polymers.Carbohydrates:Basic monomer unit is a sugar (saccharide)Therefore single monomer = monosaccharide2xmonosaccharide = disaccharideLarger numbers = polysaccharide

Test for reducing sugarsReduction- Chemical reactions involving gain of electrons. Reducing sugar can donate electrons to another chemical (in this case Benedict's reagent) Add food sample to test tube- if not already liquid then grind up into water Add equal volume of Benedict's Heat mixture Should turn from blue -> brick red if sample is a reducing sugar

DisaccharidesWhen MSacs join a molecule of water is removed (condensation reaction) forming a glycosidic bond.When water is added under suitable conditions the bond breaks (hydrolysis)

Test for non-reducing sugarsSome DSacs are reducing so 1st try Bendict's.Others need to be broken down first so: Test with Benedict's to see no change Add hydrochloric acid and heat to break down into MSacs Add alkali solution as Benedict's doesn't work in acidic conditions. Re-test using Benedict's. Should now turn from blue -> brick red

PolysaccharidesCombination of many monosaccharide molecules joined by glycosidic bonds formed by condensation reactions. They are large, insoluble molecules.Example- cellulose used for structural support in plants 

StarchPolysaccharide found in many parts of a plant. Test for starch:Iodine turns from yellow -> blue black in prescence of starch. 

Lactose intoleranceLactose is the sugar found in milk and is hydrolysed by the enzyme lactase.Milk forms the diet of babies so they produce large amounts of lactase but production naturally diminishes as less milk consumed. However some end up producing little or no lactase.As a result some people cannot digest the lactose which they consume. When undigested lactose reaches the large intestine, microorganisms break it down producing a large volume of gas. Problems- consuming efficient calcium in the absence of milkSolution- Adding the enzyme lactase to milk before drinking it.

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