Complex carbohydrates: structural polysaccharides

• what is cellulose made from?

  long chains of up to 15,000 beta-glucose monomers
• what are the properties of cellulose?

  • very high tensile strength
  • straight chains
  • hydrogen bonds form with chains to prevent spiralling
  • parallel chains form hydrogen bonds between them to form 'bundles'
• what is the molecular structure of cellulose?

  • beta-glucose molecules joined by beta-1, 4-glycosidic bonds in a condensation reaction
  • the orientation of the beta-glucose molecules alternate
• what is the structure of cellulose?

  • beta-glucose chains form 'bundles' called Microfibrils - these are formed from 60-70 chains with a 10-30nm diameter
  • groups of Microfibrils form Macrofibrils - formed from 400 Microfibrils embedded in a 'glue' called in pectin in the plant cell wall
  • cellulose fibres are criss-crossed so there are always strong covalent bonds in the direction of the force
• what is the role of pectin?

  cell adhesion and wall hydration
• what are the roles of cellulose?

  • provides shape and rigidity to cell wall - structural support (high tensile strength of cellulose fibres present is responsible for this)
  • due to fibres, plant cells do not burst like animal cells when placed in a hypotonic solution
• how do turgid cells help to keep green stemmed plants upright?

  • rigid cell wall pushes back as water flows into cells - collectively gives strength
  • turgid cells exert an outward force on the cells surrounding them
  • they are able to support the weight of cells above them without collapsing
• what is the function of chitin?

  building material that gives strength to the exoskeleton of crustaceans, insects and the cell wall of fungi -arthropods
• why is cellulose difficult to digest?

  is made of beta-glucose which humans don't have the correct enzyme to break down beta-1, 4-glycosidic bonds (we can't hydrolise them)
• what role does cellulose play in the human digestive system?

  fibre - gives intestines exercise, keeping them healthy