Carbohydrates 5.0 / 5 based on 1 rating ? BiologyBiological moleculesASOCR Created by: Rachael1999Created on: 15-12-15 10:08 GLUCOSE C6H12O6. Monosaccharide composed of 6 carbons = hexose monosaccharide. Carbons are numbered clockwise beginning with 1C being to the right of the O within the ring. Alpha and Beta - OH group on 1C position. Polar and soluble in water. This is due to the hydrogen bonds thar form between the OH and H2O. Solubility is important because glucose needs to be dissolved in the cytosol of the cell. 1 of 9 CONDENSATION REACTIONS Two alpha glucose side by side = two OH groups interact. Bonds are broken and new bonds are reformed in different places producing new molecules. Condensation reaction forms a glycosidic bond. 1-4 glycosidic bond. Maltose is formed - a disaccharide. 2 of 9 OTHER SUGARS Fructose + Glucose = Sucrose. Glucose + Galactose = Lactose. Glucose + Glucose = Maltose. Fructose naturally occurs in fruit. Fructose is sweeter than glucose and glucose is sweeter than galactose. Pentose monosaccharides are sugars that contain five carbon atoms. TWO IMPORTANT PENTOSE SUGARS: RNA and DNA. 3 of 9 STARCH AND GLYCOGEN Many alpha glucose molecules joined by glycosidic bonds. Chemical energy store. Amylose - polysaccharide: Alpha glucose joined by 1-4 glycosidic bonds. Glucose twists into a helix stabilised by hydrogen bonding within the molecule. Compact and less soluble than the glucose used to make it. Amylopectin - polysaccharide: 1-6 glycosidic bonds. Also bonds formed 1-4. Branched structure. 1-6 branching points occuring once every 25 subunits. Energy store in animals is glycogen. Forms more branches than amylopectin. Coiling and branching of these polysaccharides makes them very compact which is ideal for storage. Branching speeds up storing and releasing of the glucose molecules. Amylopectin and glycogen are insoluble, branched and compact. 4 of 9 HYDROLYSIS REACTIONS Glucose is stored as starch by plants and as glycogen by animals and fungi until needed for respiration. Starch or glycogen undergo hydrolysis reactions. Reactions catalysed by enzymes. Break the glycosidic bonds. 5 of 9 CELLULOSE Beta glucose molecules. Unable to join in the same way alpha moleules do. To overcome this, alternate beta glucose molecules are turned upside down. When a polysaccharide is formed from glucose in this way, it is unable to coil or form branches. A straight chain molecule is formed - Cellulose. Hydrogen bonds form microfibrils. Microfibrils join to make macrofibrils. Macrofibrils join to make fibres. Fibres are necessary for a healthy digestive system. 6 of 9 BENEDICT'S TEST FOR REDUCING SUGARS Place sample in boiling tube. Add an equal volume of benedict's reagent. Heat the mixture gently in a water bath over 80 degrees C for five minutes. A positive result will be a brick-red precipitate. The more reducing sugar present, the less blue copper 2+ ions are left in the solution. Qualitative. 7 of 9 BENEDICT'S TEST FOR NON-REDUCING SUGARS Carry out the reducing sugar test and you should obtain a negative result. E.G. Sucrose. Sucrose is boiled in dilute hydrochloric acid at above 80 degrees C in a water bath for 5 minutes. It is then neutralised with sodium hydrogen carbonate. Test with Benedict's again and then there should be a positive result. This is because the sucrose has been hydrolysed into glucose and fructose (both reducing sugars). 8 of 9 IODINE TEST FOR STARCH Put a few drops of iodine dissolved in potassium iodide solution onto the sample. (Iodine solution). Yellow/brown to blue/black colour change is a positive result. 9 of 9
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