Cell Wall Structure and Function | Free Biology Notes

In this article we will discuss about:- What is cell wall?, Characteristics of Cell Wall, Cell Wall Structure, What is Pits and its types and Functions of cell wall

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