Carbohydrates

• Carbohydrates are made from carbon, hydrogen and oxygen
• Main functions = energy storage, structural
• Glucose has the formula C6H12O6
• Disaccharides have monosaccharide sugar units joined by glycosidic bonds
• There are two types of glucose = alpha and beta
• Benedict's reagent tests for reducing sugars
• All monosaccharides are reducing sugars
• The disacharrides maltose and lactose are reducing sugars
• Sucrose is not a reducing sugar
• If no sugar is present, solution remains blue
• If low amount of sugar, solution turns green
• If medium concentration of sugar, solution turns yellow/orange
• If high concentration of sugar, solution turns red
• Maltose is made of two alpha-glucose molecules
• Lactose is made from one glucose and one galactose molecule
• Examples of monosaccharides = glucose, fructose, galactose
• Examples of disaccharides = sucrose, maltose, lactose
• Sucrose is made up of glucose and fructose.
• A 1-4 glycosidic bond connects Carbon 1 and Carbon 4
• To test for non-reducing sugars, the sugar solution is boiled in acid first
• Method for Benedict's

  • Add Benedict's reagent to sample
  • Heat and mix
• Method for non-reducing sugars

  • Boil with hydrochloric acid
  • Neutralise with sodium hydrogencarbonate
  • Carry out Benedict's test
• Glycogen is made of alpha-glucose monomers
• Glycogen is composed of 1-4 and 1-6 glycosidic bonds
• Glycogen is the form of energy storage in animals
• Glycogen role

  • Loads of side branches - stored glucose can be released quickly
  • Compact - good for storage
• Cellulose is made of beta-glucose molecules
• Cellulose is made from long unbranched chains and has hydrogen bonds forming cross bridges
• Cellulose is an essential component of cell walls
• Cellulose Role

  • Provides rigidity to cell walls
  • Prevents cell from bursting as water enters it - exerts inward pressure making it turgid
• Starch is made from alpha-glucose
• Starch is a mixture of amylose and amylopectin
• Starch is used for energy storage in plants
• Amylose is a straight chain polymer with no branches, so can pack tightly together
• Amylose forms helical coils which are held together by weak intermolecular forces (hydrogen bonding)
• Starch Role

  • coiled structure - compact
  • side branches - enzymes get to glycosidic bonds easily
  • insoluble - does not affect osmotic gradients
  • large - doesn't leave cell
• Amylopectin is a branched structure with mostly 1-4 glycosidic bonds and some 1-6
• Glycogen is similar in structure to amylopectin, but has shorter chains and is more highly branched