Carbohydrates

• The three main types of carbohydrates are monosaccharides (simple sugars), disaccharides (double sugars) and polysaccharides (long chains).
• Roles of carbs:

  1. Source of energy in respiration e.g starch, glycogen
  2. Building blocks for larger molecules e.g ATP, RNA, DNA
  3. Structural support e.g cellulose
• Monosaccharides

  • soluble, sweet
  • molecular formula: CnH2nOn
• Glucose

  • has 2 isomers, α-glucose and β-glucose
  • same molecular formula, same chemical substance, different form

  
• Disaccharides

  • soluble, sweet
  • formed from 2 monosaccharides through condensation
  • 1 hydroxyl group (-OH) + hydrogen atom (H)
  • produce 1 water molecule
  • glycosidic bond formed
• Polysaccharides

  • made via condensation
  • not sweet, insoluble

  e.g starch, glycogen, cellulose
• Starch

  • storage molecule in plants
  • food reserve
  • amylase + amylopectin

  amylose

  • α-1,4-glucose
  • long linear branch

  amylopectin

  • branched molecule
  • α-1,4 and 1,6-glucose
  • 2 up (1,6) 4 down
• Glycogen

  • storage of carbs in animals
  • α-1,4 and 1,6-glucose
  • form granules when clumped together
  • abundant in liver and muscle cells
• Cellulose

  • structural role in plant cells walls
  • high tensile strength
  • prevent cell bursting
  • helps cell withstand turgor pressure
  • fully permeable
  • β-1,4-glucose
  • forms fibres
• Advantages of glycogen being highly branched

  It is more compact and so can store more glucose, the branching enables more free ends where glucose molecules can either be added or removed, allowing for condensation and hydrolysis reactions to occur more rapidly