Carbohydrates

• Monosaccharides

  Carbohydrates made from: carbon, hydrogen, oxygen atoms. Monosaccharides = made from simple sugars containing 3-7 carbon atoms and are soluble in water
• Monosaccharides

  • Glucose (hexose sugar with 2 isomers)
  • Galactose (in milk)
  • Fructose (in fruit)
• Monosaccharides


  The simplest carbohydrates consisting of only 1 sugar molecule
• Glucose


  Hexose sugar C6H12O6 is an important source of energy in humans. During cellular respiration, energy released from glucose helps to make ATP (adenosine triphosphate)
• Alpha vs Beta Glucose

  Are isomers (have the same molecular formula but different arrangements of atoms in space). The carbon atoms are numbered 1-6 and the OH (hydroxyl) group are in different orientations around C1
• Disaccharides

  Sugars that are composed of 2 monosaccharides joined together in a condensation reaction forming a glycosidic bond
• Disaccharides

  • Glucose + Fructose = Sucrose (common table sugar)
  • Glucose + Glucose = Maltose
  • Glucose + Galactose = Lactose (sugar found in milk. Lactose intolerance= where the body is unable to digest it)
• Polysaccharides


  Made of the condensation of 3+ monosaccharides joined by glycosidic bonds. Chains may be branched or unbranched. Chains may contain different types of monosaccharides
• Polysaccharides


  • Starch (made out of amylose and amylopectin, is the made polysaccharide energy store in plants, is composed of a-glucose)
  • Glycogen (polysaccharide energy store for animals, composed of a -glucose)
  • Cellulose (structural component of plant cell walls, composed of long unbranched chains of b -glucose)
  • Chitin
• Starch


  • Function: Main energy storage material in plants. Stored in seeds of plants. Broken down into glucose by plants when they need more energy. Can act as a source of food for humans & animals. Does not change the water potential in a cell because it's insoluble in water. Chains= branched or unbranched. When hydrolysed forms a-glucose (=easily transported readily used in respiration)
• Iodine Test for Starch

  1. Place a small sample in dimple of spotting tile or boiling tube

  2. Add few drops iodine solution

  3. Observe any colour changes

  4. If starch present: solution orange to blue-black
• Amylose

  Unbranched and good for energy storage
• Amylopectin

  Branched and good for quick energy release
• Glycogen


  • Highly branched molecule like amylopectin. Highly branched structure= glucose can be quickly released. Never in plants. Found as small granules mainly in muscles and liver. Good storage molecule as it is compact. When blood glucose levels decrease: glycogen broken down to release glucose (glycogenolysis)
• Cellulose


  • Long chain of beta glucose. B-glucose molecules are linked by glycosidic bonds to form linear cellulose chains that are unbranched. Microfibrils are strong fibres that are made of many cellulose chains held together by hydrogen bonds. Cellulose chains -> microfibrils-> fibres. Most abundant natural polymer. Cell walls mostly made from cellulose (offer structural support because of the strength of the microfibril fibres)
• Cellulose cannot be broken down by human digestive enzymes. Herbivores eg cows and horses are able to digest plant material rich in cellulose
• Benedict's Test


  Test for reducing & non-reducing sugars
• Reducing Sugars

  All monosaccharides are reducing sugars (eg glucose, galactose, fructose). Some disaccharides are reducing sugars (eg lactose and maltose). Reducing sugars= can act as reducing agents (can donate electrons)
• Benedict's Test for Reducing Sugars

  1. Place 2ml of substance in boiling tube (substance MUST be liquid)

  2. Add 10 drops of Benedict's solution

  3. Place in boiling water bath for 3-5 mins

  4. Blue solution= non reducing sugar. Green/ yellow precipitate= traces of reducing sugar. Orange/ red precipitate= moderate amount of reducing sugar. Brick red= large amount of reducing sugar
• Test for Non-Reducing Sugars

  1. Boil in dilute HCL (hydrolyse the non reducing sugar)

  2. Neutralise the solution by adding sodium hydrogen carbonate

  3. Repeat benedict's test

  4. Pos= non reducing sugars present. Neg= no sugars present
• GLUCOSE MOLECULE: