carbohydrates

• carbohydrates are made up of monosaccharides , these are simple sugars
• when 2 monosaccharides join, they form a disaccharide which is a complex sugar

  eg. glucose + fructose = sucrose

  glucose + glucose = maltose

  glucose + galactose = lactose
• when many join, they form a polysaccharide ‘macromolecule’

  these are not sugars, they have different properties
• what are the properties of polysaccharides

  structural molecules:

  • cellulose (plant cell) - long chains of b glucose

  energy storage molecules:

  • starch (plant cell) - long chains of a glucose
  • glycogen (animal cell) - long chains of a glucose
• details of some monosaccharides

  can be straight chain or ring shaped.

  glucose is monosaccharide and can exist in 2 forms: alpha( OH group at bottom of ring on c4), beta( H group at bottom of ring on c4)
• role of glucose in living organisms

  substance used in aerobic respiration inside cells to release ATP (helped by the fact it is small , soluble , reactive and easily broken down)

  all monosaccharides are sweet and water soluble simple sugars and ‘reducing sugars’
• details of some disaccharides

  form when condensation reaction occurs between 2 monosaccharides forming a 1-4 glycosidic bond

  to break down a disaccharide it would be a hydrolysis reaction requiring the addition of water and enzyme using heat or acid
• roles of disaccharides in living organisms

  easily hydrolysed back into monosaccharides and used in cellular respiration

  sucrose is main transport sugar in phloem of plants

  lactose is sugar found in mammalian milk- high energy content for suckling young
• details of some polysaccharides

  large polymers formed by joining lots of monosaccharides together by condensation reactions, joint by glycosidic bonds. (shorter chains are oligosaccharides)
• starch

  a glucose arranged as amylose and amylopectin

  amylose- 1-4 a glucose coiled into helix (stabilised by hydrogen bonds holding helix in shape)

  amylopectin- 1-4 a glucose with short 1-6 side branches
• how structure of starch makes it good storage molecule in plants

  large molecule - insoluble + unreactive so wont interfere with cellular reactions

  compact due to branched/coiled so lots stored in small place

  no osmotic effect due to being insoluble + unreactive

  easily hydrolysed to release glucose when cell needs energy