Cell Wall Structure and Function What is Cell Wall? Cel | Dr. Sajid Ali

Cell Wall Structure and Function

What is Cell Wall?
Cell wall is 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 wall 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 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 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 mature cell
It has high cellulose & less hemicelluloses content

IV) Tertiary cell wall
Laid down on secondary wall
Found in tracheids of gymnosperms

What is Pits?
Cell wall is not uniform in thickness throughout
Certain places cell wall 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