Carbohydrates

• Carbohydrates


  Molecules containing carbon, hydrogen and oxygen
• Carbohydrates


  • Used as a store of energy
  • Used as a source of energy
  • Used as structural units
• Reducing sugars


  Can donate electrons
• Non-reducing sugars


  Cannot donate electrons or be oxidised
• Monosaccharides


  • Simplest carbohydrate
  • Source of energy
  • Suitable due to many carbon-hydrogen bonds
  • Soluble in polar solvents e.g. water
  • Can exist as straight chains or in a ring or cyclic form
  • Have a backbone of single bonded carbon atoms, with one double bond to an oxygen atom (to form a carbonyl group)
  • Different sugars have different numbers of carbon atoms
• Monosaccharides


  • Glucose
  • Fructose
  • Galactose
• Disaccharides


  • Sweet and soluble
  • Made when 2 monosaccharides are joined
  • Formed by a condensation reaction to form a glycosidic bond
  • Can be broken into monosaccharides with an addition of water, in a hydrolysis reaction
• Disaccharides


  • Maltose
  • Lactose
  • Sucrose
  • Cellobiose
• Glycosidic bond


  The bond formed when two monosaccharides are joined
• Types of glycosidic bonds

  • Maltose: α 1,4
  • Sucrose: α 1,2
  • Cellulose: β 1,4
  • Amylose: α 1,4
  • Amylopectin: α 1,4 and α 1, 6
• Polysaccharides


  • Polymers of monosaccharides
  • Homopolysaccharides are made of one kind of monosaccharide
  • Heteropolysaccharides are made of more than one type of monosaccharide
  • Stores of energy
  • Compact so don't take much space
  • Can be unbranched or branched
• Polysaccharides


  • Starch
  • Glycogen
  • Cellulose
• Amylose


  Chain of α-glucose, glycosidic bond in 1,4, amylose coils into spiral (held in place by HBs), hydroxyl in spiral so less soluble so maintains structure
• Amylopectin


  α 1,4 branches at 1,6, coils in spiral held by HBs, branches emerge from spiral
• Glycogen


  α 1,4 branches at 1,6, smaller chains, so less coiling but has branches so more compact, easy to remove monomers as more ends
• Cellulose


  • In plants, forms cell walls
  • Insoluble, fibrous made of β-glucose molecules, long chains forming glycosidic bonds, up to 15,00 β-glucose molecules
  • Cellulose are straight and lie side by side
  • Hydrogen and hydroxyl on carbon 1 are inverted in β-glucose, so every other β-glucose molecule in chain is rotated by 180°, preventing spiralling
  • 60-70 cellulose chains bind to form microfibrils which then bundle to form macrofibrils embedded in pectins to form cell wall
• Bacterial cell walls


  • Made of peptidoglycan, made from long polysaccharide chains that tie in parallel, cross linked by short peptide chains, made of amino acids
• Exoskeletons


  • Insect and crustacean exoskeletons made of chitin, which instead of a hydroxyl group on carbon 2, has an acetyl amine group (NHOCCH₃), forms cross links between long parallel chains of acetylglucosamine