Cell Wall

• Cell walls are found in plant cells but not animal cells.
• The cell wall is made up of polysaccharides, such as pectin and cellulose.
• Plant cells have a rigid cell wall that provides support to the cell.
• Primary Cell Wall Components:

  • Cellulose (microfibril phase)
  • Pectin & Hemicellulose + protein extensin (matrix phase)
• Synthesis of primary cell wall components:

  1. Cellulose microfibril- synthesised in the plasma membrane
  2. pectin and hemicellulose- in the golgi apparatus is transported to the cell wall via vesicles.
  3. Extensin protein- synthesised from the rough endoplasmic reticulum and carried by vesicles which fuse with plasma membrane.
• Function in regulating Cell Shape:

  • Provide structural Support
  • influence morphology
  • Prevents excessive water uptake
• Secondary Cell Wall:

  • produced only after cell growth has stopped
  • thicker and stronger than primary wall
• Not all plant cells have a secondary Cell wall
• Secondary wall provides more structural support than primary wall. When cell dies, it creates ring that allow osmosis.
• Function: Influence Cell Morphology

  • orientation of cellulose microfibrils influence morphology.

  1. Randomly oriented: cells expand EQUALLY in all directions.
  2. Right angles to long axis of cell wall: cell wall expand longitudinally.
• Provide Structural Support:

  • protoplast pushes against cell wall= RIGID which gives the cell shape.
• Protein Extensin:

  • control extensibility of cell
  • creates cross-linking of pectin and cellulose= dehydrates cell wall, therfore, reduces extensibility of cell= STRENGTH.
• Cell wall’s prevention of excessive water uptake:

  • Vacuole play an important role in this process as it contains water and make up a large portion of the protoplast.
  • Vacuole take up water through osmosis to equilibriate high solute content inside cell. Then the cell wall limits the water uptake, therefore, preventing the cell from bursting.
• Secondary Wall Structure:

  • Contains Lignan (2nd most abundant after cellulose) which provide strength and rigidity.
  • More Cellulose and less Pectin
  • Has Multiple layers
  • Microfibrils in each layer have different orientation which gives the cell strength.
• Middle Lamella:

  • hemi-cellulose rich
  • acts as a cementing material binding 2 cells together
• Plasmodesmata:

  • allows cytoplasmic continuity between two cells and allow cytoplasmic exchange.
• Cellulose

  • Major component within the plant cell
• Cellulose is the most abundant macromolecule in a plant cell. It is a

  highly ordered glucose Polymer.
• Cellulose forms MICROFIBRILS (strong) which is an essential component in both the primary and secondary cell wall.
• Hemicellulose:

  • heterogeneouS group of polysaccharides
  • a long chain is branched with shorter protruding chains which forms the rigid structure.
• Pectin:

  • branched negatively charge polysaccharide
  • binds water
  • have gel-like properties