Introduction

Structure and function of bacterial cell

Structure and function of bacterial cell: A bacterial cell have essential structural components : cell wall, cytoplasm membrane , intra cytoplasm structure and cell surface appendages ( capsule , flagella , fimbriae , spore ). The biochemical compositions of these structures are macromolecules are arranged or sequenced in primary – structure of molecule in which the subunits are put together such as:

DNA, RNA ---------- Nucleotides

Protein --------------- amino acid

Phospholipid -------- fatty acid

Polysaccharide ------- sugars

Cell wall

The bacteria are surrounding by rigid cell wall. The principle structural component of cell wall is peptidoglycan. The cell wall consists of polymer of two sugar derivatives N- acetylglucosamine and N- acetylmuramic acid cross linked by short chains of amino acids (peptide), this molecule is a type of peptidoglycan called murein Peptidoglycan (PG) is complex of polysaccharide and polypeptide. Most bacteria are classified according to reaction of Gram stain with components of cell wall into major groups; Gram positive & Gram negative bacteria based on staining properties. Gram stain developed in 1884 by Christian Gram ,the most widely employed in bacteriology lab.

Gram positive bacteria cell wall composed of :

-Peptidoglycan This layer is very thick in G +ve bacteria constituting 50-80nm of cell wall and responsible for the rigidity of cell wall and retention of crystal violet dyes during the Gram stain procedure. The large amounts of PG make Gram positive bacteria susceptible to antibiotics (penicillin) that inhibit cell wall synthesis.

-Teichoic acid and thin layer of lipid

Gram negative bacteria cell wall composed of :

-Inner layer of peptidoglcan

This layer is thin constituting of (5-10) nm of cell wall which cannot retain the

crystal violet stain.

-Outer layer of lipopolysaccharides (LPS)

cotaining of lipid A (endotoxin) and polysaccharide (fig.).

-Periplasmic space between the inner and outer layers

It is filled with gel and is crossed by lipoprotein molecules to link the

peptidoglycan layer and LPS layer, and no teichoic acid.

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