Carbohydrates

• Monosaccharide


  A single sugar unit
• Polysaccharide


  When two or more monosaccharides are linked to form a polymer.
• Glucose

  Hexose monosaccharide
• Alpha glucose

  
• Beta glucose

  
• Glucose molecules are soluble due to the hydrogen bonds that form between the hydroxyl groups and water molecules.
• Condensation reaction of glucose


  When the hydroxyl groups of two glucose molecules are next to each other, they begin to interact and this causes bonds to break and a new bond between an oxygen and the carbon 4 on one molecule and the carbon 1 on the other molecule.
• Condensation reactions form polymers from monomers by joining monomers together, also producing water.
• Maltose

  
• Sucrose

  Fructose + glucose
• Lactose

  Galactose + Glucose
• Ribose

  Pentose monosaccharide
• Starch

  Long chains of amylose and amylopectin.
• Amylose

  Alpha glucose molecules joined together by 1-4 glycosidic bonds in the shape of a helix, stabilised by hydrogen bonds within the molecule. This makes the polysaccharide more compact and much less soluble than its monosaccharide.
• Amylopectin: the non-crystallizable form of starch, consisting of branched polysaccharide chains.
• Starch is used as a storage molecule in plants.
• Glycogen: a substance deposited in bodily tissues as a store of carbohydrates. It is a polysaccharide which forms from glucose on hydrolysis.
• Glycogen has more branches than starch as animals have a greater metabolic requirement for energy as they are more active than plants.
• Hydrolysis reactions are the breaking of bonds between molecules using water as a catalyst
• To release glucose for respiration, starch or glycogen undergo hydrolysis reactions, requiring the addition of water molecules, catalysed by enzymes.
• Cellulose

  Beta glucose molecules joined together by 1-4 glycosidic bonds. Alternate beta glucose molecules are turned upside down to form this bond.
• Cellulose

  
• Cellulose molecules make hydrogen bonds with each other forming microfibrils, which can join together to form long fibres. These fibres are strong and insoluble and are used to make cell walls.
• It is difficult for humans to break down cellulose down into its monomers, but the fibres it forms are necessary for a healthy digestive system.
• Benedict's test


  Carbohydrates
• Benedict's test for reducing sugars:

  1. Add equal volume Benedict's reagent.
  2. Heat mixture in a boiling water bath for five minutes.
  3. A positive test will produce a brick-red precipitate.
• Benedict's test for non-reducing sugars


  Boil the normal test with hydrochloric acid. The colour changes according to the concentration of sugars present - blue is none, red is high.
• Test for Starch


  Iodine
• Iodine test for starch


  A few drops of iodine dissolved in potassium iodide solution mixed into a solution. If the solution changes from yellow/brown to blue/black, starch is present in the sample.
• Carbohydrates contain carbon, hydrogen and oxygen.