What is Cell Wall?
=> Cell wall is a rigid and protective layer around the plasma membrane
=> Discovered by Robert Hooke in 1665
=> Cell wall non-living rigid structure
=> Found in plants, fungi, prokaryotes and protists
=> Composition of cell walls varies in different groups
Characteristics of Cell Wall
=> Cell wall is a rigid and protective layer around the plasma membrane
=> It is a non-living structure
=> Animal cells do not have a cell wall
=> Found in most plant cells, fungi, bacteria, algae, and some archaea
=> Cell wall has many important functions in a cell including protection, structure, and support
Cell Wall Structure
Structure of Prokaryotes Cell Wall
=> Cell wall is made up of peptidoglycon
=> Peptidoglycan is made up of polysaccharide chains cross-linked by unusual peptides containing D-amino acids
=> A notable difference between the cell walls of gram-positive and gram-negative bacteria is the substantially thicker peptidoglycan layer in gram-positive bacteria.
=> Cell wall of gram-positive bacteria contains teichoic acids
Structure of Fungi Cell Wall
=> Fungal cell wall is made up of three main components
Chitin
=> Polymers consisting mainly of unbranched chains of β-(1,4)-linked-N-Acetylglucosamine in the Ascomycota and ➖ Basidiomycota, or poly-β-(1,4)-linked-N-Acetylglucosamine (chitosan) in the Zygomycota
=> Both chitin and chitosan are synthesized and extruded at the plasma membrane
Glucans
=> Glucose polymers that function to cross-link chitin or chitosan polymers
=> β-glucans are glucose molecules linked via β-(1,3)- or β-(1,6)- bonds and provide rigidity to the cell wall while α-➖ ➖ glucans are defined by α-(1,3)- and/or α-(1,4) bonds and function as part of the matrix
Proteins
=> Enzymes necessary for cell wall synthesis and lysis in addition to structural proteins are all present in the cell wall.
=> Most of the structural proteins found in the cell wall are glycosylated and contain mannose, thus these proteins are called mannoproteins or mannans.
Structure of Plant cell wall
=> Cell wall is made up of 4 layers
=> Middle lamella, primary, secondary and tertiary wall
I) Middle lamella
=> Cementing layer between the cells
=> It is made up of ca & mg pectates
II) Primary cell wall
=> Found in growing cell
=> It has high hemicelluloses & less cellulose content
III) Secondary cell wall
=> Found in the mature cell
=> It has high cellulose & less hemicelluloses content
IV) Tertiary cell wall
=> Laid down on the secondary wall
=> Found in tracheids of gymnosperms
What are Pits?
=> Cell wall is not uniform in thickness throughout
=> Certain places cell walls are not laid down, such places are called pits
Pits are of two types
I) Simple Pit
=> Pit chamber is uniform in diameter
=> Found in angiosperms
II) Bordered pit
=> Pit chamber is flask-shaped
=> Found in gymnosperms
=> Number of plasmodesmata or cytoplasmic strands are present in pit
Functions of cell wall
=> Maintains shape of the cells
=> Protects cell from mechanical injury
=> Allows materials to pass in and out of the cell
=> Prevents undue expansion of cell when water enters by osmosis