AQA A Level Biology复习笔记1.1.9 Cellulose

Cellulose: Structure & Function

 

  • Cellulose is a polysaccharide
  • Polysaccharides are macromolecules that are polymers formed by many monosaccharides joined by glycosidic bonds in a condensation reaction to form chains. These chains may be:
    • Branched or unbranched
    • Folded (making the molecule compact which is ideal for storage, eg. starch and glycogen)
    • Straight (making the molecules suitable to construct cellular structures, eg. cellulose) or coiled
    • Polysaccharides are insoluble in water

     

Cellulose – structure

  • Is a polymer consisting of long chains of β-glucose joined together by 1,4 glycosidic bonds
  • As β-glucose is an isomer of α-glucose to form the 1,4 glycosidic bonds consecutive β-glucose molecules must be rotated 180° to each other

 

2.2.1-Formation-of-Sugars-1To form the 1,4 glycosidic bond between two β-glucose molecules, the glucose molecules must be rotated to 180° to each other

 

  • Due to the inversion of the β-glucose molecules many hydrogen bonds form between the long chains giving cellulose it’s strength

Cellulose_-hydrogen-bond-formation-between-chains

 

Cellulose is used as a structural component due to the strength it has from the many hydrogen bonds that form between the long chains of β-glucose molecules

 

Cellulose – function

  • Cellulose is the main structural component of cell walls due to its strength which is a result of the many hydrogen bonds found between the parallel chains of microfibrils
  • The high tensile strength of cellulose allows it to be stretched without breaking which makes it possible for cell walls to withstand turgor pressure
  • The cellulose fibres and other molecules (eg. lignin) found in the cell wall form a matrix which increases the strength of the cell walls
  • The strengthened cell walls provides support to the plant
  • Cellulose fibres are freely permeable which allows water and solutes to leave or reach the cell surface membrane
  • As few organisms have the enzyme (cellulase) to hydrolyse cellulose it is a source of fibre

 

Cellulose_-Structure-linking-to-function-of-cellulose

 

The strength and insolubility of cellulose fibres means it is a suitable molecule to construct cell walls

 

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