Cellulose (Cambridge (CIE) A Level Biology): Revision Note

Cellulose: structure & function

• Cellulose is an unbranched 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, e.g. starch and glycogen)

    • Straight (making the molecules suitable to construct cellular structures, e.g. 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

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

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 (e.g. 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