carbohydrates

• carbohydrates

  • only contain C,H and O
  • general formula Cx(H20)y
• Glucose

  • Hexose monosaccharide (6 carbons)
  • Polar and soluable (due to hydrogen bonds between hydroxyl groups and water molecules)
• Starch

  • polysaccharide
  • glucose -> starch -> amylose + amylopectin
  • compact and easily broken down by enzymes
  • alpha glucose
  • how plants store energy
• Amylose

  • compact
  • 1,4 glycosidic bonds only
  • forms a helix
  • unbranched
• Amylopectin

  • branched
  • enzymes break down quickly because they attach at the end of each branch
  • 1,4 glycosidic bonds and 1,6 glycosidic bonds
  • insoluable to stop water entering the cell
• Glycogen

  • polysaccharide
  • glucose -> glycogen
  • compact and good for storage
  • alpha glucose
  • branched for quick release (amylopectin on crack)
  • 1,4 glycosidic bonds and 1,6 glycosidic bonds
  • more branched because animals are mobile
  • insoluable
• Hydrolysis reaction


  To release glucose for respiration, starch or glucogen undergo hydrolysis

  Addition of water molecules to reverse condensation reactions

  catalysed by enzymes
• Cellulose

  • Beta glucose (can't join like alpha glucose can only join of alternating glucoses are upside down)
  • when a polysaccharide is joined like this it cannot coil or make branches
  • it forms a straight chain molecule
  • Cellulose molecules make H+ molecules forming microfibrils (these join together to make macrofibrils)
  • strong and insoluble
  • necessary for healthy digestive system
• Benedict's test for reducing sugars

  reducing sugars - all monosaccharides and some disaccharides

  means they can donate electrons or reduce another molecule/ chemical

  Benedict's reagent - alkaline solution containing copper (II) sulfate
• Benedicts test for reducing sugars - steps

  1. Place sample in boiling tube (grind or blend if not liquid)
  2. Add an equal volume of Benedicts reagent
  3. Heat mixture in a boiling water bath for five minutes
• Benedicts test for reducing sugars - results

  • Reducing sugars will react with copper ions in benedicts
  • Results in addition of electrons to the blue Cu2+ ions reducing them to brick red Cu2+ ions
  • Brick-red precipitate = positive result
  • Qualitive
  • Higher concentration = more precipitate
• Benedicts test non-reducing sugars 


  Do not react with benedicts

  If sucrose is boiled with hydrochloric acid it will then give a positive result when warmed with benedicts. this is because the non-reducing sugar has been hydrolysed by the acid to a reducing sugar
• Iodine test for starch - steps

  1. A few drops of potassium iodide with dissolved iodine in are mixed with the sample
• Iodine test for starch - results 


  If solution changes colour from yellow/brown to purple/black starch is present
• Alpha glucose


  hydroxyl group is found below

  H

  <

  OH
• Beta Glucose


  Hydroxyl group is found above

  OH

  <

  H
• functional groups 


  OH - alcohol

  COOH - carboxylic acid

  NH2 - amine group
• monosaccharides


  simple sugars

  (CH2O)n
• Monomer 


  A single glucose unit

  Capable of linking to others
• Condensation reaction 


  Two carbohydrate molecules bond together forming a water molecule

  The link is a glycosidic bond

  To break glycosidic bonds you use a water molecule (hydrolysis)