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what are carbohydrates

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1. 1. carbs are substacnes that contain the elements carbon hydrogen and oxygen

2. 2. they have the general formula cx(h2o)y

three main classes:

monosaccharides, disaccharides and polusacchirdes

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monosaccharides?

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1. 1. defined as a carb which cannot be hydrolysed to simpler carbohydrates

2. 2. general formula of : (ch2o)n

3. eg: glucose, fructose, galactose

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disaccharides

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1. 1. a disaccharide is formed by a condensation reaction between two monosaccharides during which one molecule of water is removed from the pair of monosaccharides and the bond formed between the two monosaccharide is a glycosidic bond

2. 2. maltose is glucose + glucose,

3. 3: fructose : glucose + sucrose

4. 4: lactose: glucose + galactose

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polysaccharides

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1. 1. polymers of monosaccharides

2: starch --> storage polysaccharide in plants

3: glycogen --> storage polysaccharide in humans

4: cellulose --> structural polysaccharide in plants

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structure of starch

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starch is a polymer of glucose and has two components, amylose and amylopectin

1. amylose : has a straight chain structure with helical shape for a more compact structure

2. and it consists of several thousand glucose units joined by glycosidic bonds

3. amylopectin : has a compact but highly branched structure with the glucose units between and within the branched held together by glycosidic bonds and it has twice the amount of glucose units as amylose

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function of carbohydrates

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1. 1. as a source of energy

2. 2. sucrose is a very good transport sugar in the phloem of plants because its very soluble and thereforre can be moved in high concentrations and it is chemically unreactive

3. 3: polysaccharides like starch and glycogen are good storage molecules because they are large and insoluble hence indiffusible through partially permeable membranes, they have compact shapes to allow more carbohydrates to be stored in cells and they are easily hydrolysed into monosaccharides

4. 4: cellulose is a good structural polysaccharide because : it is found in all plant cell walls, hence is good cell wall material it has good tensile strength and remains permeable to water and solutes

5. 5: monosaccharides are required for the synthesis of nucleic acids and disaccharides and polysaccharides

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test for reducing sugar

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1. 1. reducing sugars are all monsaccharides and lactose and maltose

2. 2.: conduct benedicts test

3. 3: principle : this test makes use of the ability of these sugars to reduce copper form a valency of 2 to 1. the test involves the use of an alkaline solution of copper 11 sulfate which is reduced to insoluble copper i oxide detected as a brick red precipitate

   4: method : to 2cm3 of the test sample in a test tube add an equal volume of benedicts solution, mix well and place text tube in boiling water bath for two minutes and observe colour changes

4. 5: semi quanititive test

blue -> green -> yellow -> brown -> red (suspension)

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test for non reducing sugar

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1. 1. if reducing sugar test turns out negative by remaining blue, carry our this test

2. 1. to 2cm3 of test sample in a test tube add a few drops of hydrochloric acid

3. 2: heat the mixture for two mintues in a hot water bath to hydrolyse any sucrose present and split into glucose and fructose

4. 3: after two minutes neutralise the acid by adding sodium hydrogen carbonate until effervescence stops

5. 4:carry out benedicts test again, if present, then test postive now since non reducing sugar has been broken down into reducing sugars

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test for starch

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1. 1. iodine test

2. method :

3. 1. add a few drops of iodine - potassium solution to a test sample in a test tube or a white tile

4. 2: observe colour changes

5. 3: if positive, brown solution turns dark blue because the iodine takes up the position in the centre of the amylose helix to form a dark blue starch - iodide complex

6. 4: if negative : solution remains brown