Carbohydrates

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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.
  • (http://adashofscience.com/wp-content/uploads/sites/3/2013/05/glucose-alpha-beta.png)
  • 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.
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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.
  • (http://images.tutorvista.com/cms/images/38/glycosidic-linkage.png)
  • Condensation reaction forms a glycosidic bond.
  • 1-4 glycosidic bond.
  • Maltose is formed - a disaccharide.
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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.
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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.
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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.
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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.
  • (http://3.bp.blogspot.com/-IQeCB5BtWWo/UksFut6qL6I/AAAAAAAADps/DHmf9jQK3k8/s1600/cellulose+backbone+beta+1+4+glycoside+bond.png)
  • Hydrogen bonds form microfibrils.
  • Microfibrils join to make macrofibrils.
  • Macrofibrils join to make fibres.
  • Fibres are necessary for a healthy digestive system.
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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.
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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).
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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.
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