Cellulose (AQA A Level Biology): Revision Note

Cellulose: structure & function

• Cellulose is a polysaccharide found in plant cells

Structure

• Cellulose consists of long chains of the monomer 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 its strength

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 provide 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