Carbohydrates

• • Most carbohydrates are polymers.
  • Polymers are large, complex molecules composed of long chains of monomers joined together.
  • Monomers are small basic molecular units e.g monosaccharides, amino acids and nucleotides
• • Carbohydrates are made from monosaccharides e.g glucose , fructose and galactose
  • Glucose is a hexose sugar ( 6 carbon atoms )
  • Two types of glucose = alpha and beta (they’re isomers - same molecular formula but connected differently)
• What is a condensation reaction ?

  Its when two molecules join together with the formation of a new chemical bond and a water molecule is released
• glucose + glucose = maltose

  glucose + fructose = sucrose

  glucose + galactose = lactose
• • monosaccharides are joined together by condensation reactions
  • a glycosidic bond forms between two monosaccharides as water molecule is released
  • a disaccharide is formed when two monosaccharides join together
• • polymers can be broken into monomers by a hydrolysis reaction as it breaks the chemical bond between the monomers using a water molecule
• BENEDICTS TEST FOR RS

  • rs include all monosaccharides ( e.g glucose )and some disaccharides (e.g maltose, lactose )
  • add benedict’s reagent (blue) to a sample and heat in boiling water bath, if positive result it would form coloured precipitate
  • positive result = blue to (brick red) b-g-y-o-r (depending on concerntration)
  • negative result = stay blue
• BENEDICTS TEST FOR NRS (e.g sucrose )

  • if test for rs is negative you have to break sample down into monosaccharides by adding dilute HCI and bring to boil in water bath then neutralise sample with sodium hydrocarbonate and redo benedicts test
  • positive result = blue to (brick red) b-g-y-o-r (depending on concerntration)
  • negative result = stay blue
• • plants store excess glucose as starch which is a mixture of two polysaccharides of a-glucose - amylose + amylopectin
  • Amylose = long unbranched chain of a-glucose , angles of glycosidic bonds give it helical structure making it compact
  • Amylopectin = long branched chain of a-glucose allowing enzymes that break the molecul down reach the glycosidic bond easily = glucose released quickly 1,4 and 1,6 links
  • starch is insoluble , doesn’t effect water potential or osmotic balance, found in chloroplasts
• IODINE TEST FOR STARCH

  • add iodine dissolved in potassium iodide solution to sample
  • starch present = orange to blue/black
• • animals store excess glucose and glycogen ( polysaccharid of a-glucose 1,4 carbon bonds)
  • has side branches meaning stored glucose can be hydrolysed released quickly providing more energy for respiration
  • compact and insoluble
• • cellulose is made of long unbranched chains of b-glucose held by 1,4 carbon bonds (every other has to flip 180° )
  • b-glucose moleclues bond forming straight cellulose chains
  • cellulose chains linked by hydrogen bonds to form strong fibres called microfibrils providing structural support e.g cell wall