Cell Wall Structure and Function

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