Cell Envelope: The cell envelope is made up of the cell membrane, the cell wall, and, if present, the outer membrane. This envelope is typically found in prokaryotes such as bacteria and consists of the inner cell wall and the bacterium's outer structure. The cell envelope serves an important structural role in the cell. It protects prokaryotes from internal turgor pressure caused by their high macromolecule concentration. Bacterial cell envelopes can be divided into Gram-positive and Gram-negative cell walls. For NEET aspirants, the following article will detail the cell envelope and its constituents.
The bacterial cell envelope acts as a protective barrier, shielding the cell from the outside environment. Scientists have used the Gram-staining technique for over a century to classify bacteria based on how they react to specific dyes. This method classifies bacteria into two types: Gram positive, which retains the stain, and Gram negative, which does not.
However, bacterial classification goes beyond staining properties. Prokaryotes are now classified into 30 Bacteria and 5 Archaea phyla based on factors other than staining behavior. Advances in genetic research have altered our understanding of bacterial phylogeny, emphasizing the importance of envelope composition and cell structure.
Bacterial envelopes are now classified according to the number of membranes they contain: diderms have two membranes, whereas monoderms have one. The presence or absence of lipopolysaccharides (LPS) in diderm envelopes is also important for classification.
This chapter provides an overview of recent research into the composition and structure of bacterial cell envelopes. It emphasizes the variety of envelope structures that all work toward the same goal of bacterial survival and protection in their environment.
The protective layers that surround bacterial cells are essential for maintaining cell structure and function. These layers include:
The composition and function of the cell envelope vary among bacterial species. Bacteria can be categorized based on the different types of cell envelopes they possess. Bacteria are classified into two types based on a method known as gram staining.
These bacteria have a strong outer layer of peptidoglycan, like a protective shield that keeps the purple dye from leaking out during gram staining. They also have some special acids, one of which is called teichoic acid, which gives them a negative charge. Teichoic acid bonds with certain molecules, making them negatively charged.
These bacteria have a thinner peptidoglycan layer compared to gram-positive ones. Because of this, the purple dye used in gram staining can easily wash away from them. Instead of teichoic acid, they have lipopolysaccharides, which also give them a negative charge. These lipopolysaccharides help protect them from certain drugs.
Aside from the two main types, there is another type of bacteria known as mycobacteria. These bacteria differ from gram-negative bacteria because they lack an outer membrane. Instead, they have a unique cell wall composed of arabinogalactan, peptidoglycan, and mycolic acid. This distinctive cell wall serves as a strong barrier around them.
Bacterial cell envelopes serve several important functions that aid in their survival and growth:
Overall, the cell envelope is a multifunctional bacteria structure that helps maintain cell integrity, facilitates nutrient uptake, protects against environmental threats, allows movement, and promotes interactions with other cells and surfaces.
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