Cellulose (AQA A Level Biology)

• 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

To 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 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

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