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Chapter: 11th Microbiology : Morphology of Bacteria

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Structure of Bacteria Cytoplasmic Membrane

Immediately beneath the cell wall is the cytoplasmic membrane also known as plasma membrane or cell membrane.

Structure of Cytoplasmic Membrane

Immediately beneath the cell wall is the cytoplasmic membrane also known as plasma membrane or cell membrane. It is composed of phospholipids and proteins. The phospholipids form a bilayer. Integral proteins are embedded within this bilayer. Surface proteins or peripheral proteins are loosely attached to the bilayer. The lipid matrix of the membrane has fluidity, allowing the components to move around laterally. In eubacteria, the phospholipids are phosphoglycerides, in which straight chain fatty acids are ester linked to glycerol. In archaeobacteria, the lipids are polyisoprenoid branched-chain lipids, in which long-chain branched alcohols (phytanols) are ether linked to glycerol.

 

Functions of the cell membrane

·        Prokaryotes do not have intracellular membrane bound organelles as present in eukaryotic organelles. Thus cell membrane provides a site for functions such as energy reactions, nutrient processing and synthesis.

·        It regulates transport, the passage of nutrients into the cell and the discharge of wastes. It is a selectively permeable membrane.

·        It is also involved in secretion or discharge of a metabolic product into extracellular environment.

·        Cell membrane is an important site for a number of metabolic activities. Most enzymes of respiration and ATP synthesis reside in the cell membrane since prokaryotes lack mitochondria.

 

Significance of cell envelope

·        It has toxic properties (Example: LPS)

·        It stimulates antibody production by immune system

·        The cell walls of many pathogens have components that contribute to their pathogenicity. Example mycolic acids of Mycobacterium tuberculosis

·        Cell wall is a site of action of several antibiotics.

·        Many of the serological properties of Gram negative bacteria are attributable to O antigens; they can also serve as receptors for bacteriophage attachment.

 


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