Prokaryotes - Cell Envelope and Modifications
Description:
Prokaryotic cell envelope possess chemically complex cell envelope. The cell envelope comprises of three layers: the outermost glycocalyx, the cell wall and the plasma membrane. All the three layers together act as a single protective unit.
Bacteria is classified into two groups based on the response to the gram staining method −
Gram positive Cells that take up the gram stain and are stained dark blue or purple.
Gram negative Cells that do not take up the gram stain and are stained pink or light red.
If glycocalyx is present as a loose sheath it is called slime layer. At times glycocalyx is present as thick and tough layer then it is called capsule.
The cell wall determines the shape of the cell and also provides structural support to the cell. The plasma membrane is semi-permeable in nature.
A special membranous structure called mesosome is formed by the extensions of plasma membrane into the cell.
Bacteria may be motile or non-motile based on the presence of thin filamentous extensions called flagella. Flagella helps in motility. Bacterial flagella are composed of three parts −
- Filament
- Hook
- Basal Body
Pili are elongated structures made up of pilin proteins. Fimbriae are small bristle like fibres which mostly help in attachment of the bacteria to different surfaces.