Becterial Cell Wall &Cell Membrane

By Maryam Shakeel

Becterial cell wall: The cell wall is the tough, usually flexible but sometimes fairly rigid layer that surrounds becteria. It is located outside the cell membrane 

Mostly in bacteria cell wall chemically composed of peptidoglycan (murein). The cell wall strengthens the plasma membrane and prevents the cell from bursting.

Types of becterial cell wall:

Gram +ve Gram-ve

 with the Gram stain. G+ cells are Purple

 with the Gram stain. G- cells are red.

Gram +ve Gram -ve

 Gram + Staphylococcus cells.

 Gram - E. coli cells

Gram-positive cell walls consist of many layers of peptidoglycan and also contain teichoic acids. Teichoic acids may:

bind and regulate movement of cations into and out of the cell

prevent extensive wall breakdown and possible cell lysis during cell growth

provide much of the cell wall's antigenicity

Gram +ve cell wall:

Gram-negative bacteria have a lipopolysaccharide-lipoprotein-phospholipid outer membrane surrounding a thin (sometimes a single) peptidoglycan layer. Gram-negative cell walls have no teichoic acids.

Gram-negative Cell Wall:

Electron micrograph:

G +ve G -ve

Functions of cell wall

• Does not allow motion of large molecules

• Becteria can not live without it

• Maintain the shape of cell

• From Osmolysis

Protection StructuralSupport

Filteringmechanis

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Critical Structure

Becterial cell membrane:

Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.

The plasma membrane is composed of a phospholipid bilayer (two layers) embedded with proteins and other molecules. The phospholipids are not fixed relative to each other and able to flow past each other, making the membrane fluid.

Cell Membrane or Plasma Membrane

 Bacteria can have a wide variety of fatty acids within their membranes. Along with typical saturated and unsaturated fatty acids, bacteria can contain fatty acids with additional methyl , hydroxy  or even cyclic groups. The relative proportions of these fatty acids can be modulated by the bacterium to maintain the optimum fluidity of the membrane (e.g. following temperature change).

Phospholipids are molecules composed of two long, hydrocarbon "tails" and a phosphate group "head." The hydrophilic (water-attracted) phosphate group "heads" form the internal and external surface of the plasma membrane. The hydrophobic (water-repelled) tails form the interior of the plasma membrane.

Phospholipids

Embedded in the plasma membrane are proteins that perform multiple functions, including the detection of chemicals in the cell's environment and the transportation of materials into and out of the cell.

Plasma Membrane Proteins:

the region between the cytoplasmic and outer membranes. The periplasm contains the peptidoglycan layer and many proteins responsible for substrate binding on hydrolysis  and reception of extracellular signals.

Periplasm

 passive transport of many ions, sugar and amino acids across the outer membrane. These molecules are therefore present in the periplasm.

acting as a permeability barrier for most molecules and serving as the location for the transport of molecules into the cell.

Role Of cell membrane:

prokaryotic membranes also function in energy conservation as the location about which a proton motive force is generated.

bacterial membranes (with some exceptions e.g. Mycoplasma and methanotrophs) generally do not contain sterols.

bacteria can have a wide variety of fatty acids within their membranes.

It prevents only large molecules from entering the cell.

Cell wall is completely permeable

prevents toxicity to the cell whereas cell membrane prevents entry of smaller molecules.

cell membrane is semi-permeable.

Difference Between Cell wall & memberane :

The function of the cell wall is to provide strength and rigidity to the cell.

It protects the cell against mechanical forces.

It is made up of peptidoglycan.

The cell membrane provides support to the cytoskeleton of the cell, gives shape to the cell

it maintains the potential of the cell, helps in communication with other cells, and act as molecular signals

It is made up of lipid and protein.