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== S-layer ==

The '''S-layer''' (pronounced "ess-layer") is a part of the cell envelope found in almost all [[archaea]] and many [[bacteria]]. 

=== Etymology ===

The term "S-layer" is derived from the word "surface-layer", referring to its location on the outermost part of the cell.

=== Definition ===

The S-layer is a two-dimensional crystalline layer composed of [[protein]] or [[glycoprotein]] subunits. It is the most commonly observed cell surface structure in prokaryotic organisms. The S-layer provides a protective coat to the cell and can contribute to cell shape and surface properties.

=== Function ===

The S-layer serves several functions, including providing a physical barrier against environmental threats, acting as a molecular sieve, and aiding in the adhesion to surfaces and formation of [[biofilms]]. It can also play a role in evading the host immune response in pathogenic species.

=== Related Terms ===

* [[Archaea]]: A domain of single-celled microorganisms. These microbes have no cell nucleus or any other membrane-bound organelles within their cells.
* [[Bacteria]]: A type of biological cell. They constitute a large domain of prokaryotic microorganisms.
* [[Protein]]: Large biomolecules and macromolecules that comprise one or more long chains of amino acid residues.
* [[Glycoprotein]]: Molecules that consist of a protein with one or more covalently attached carbohydrates.
* [[Biofilms]]: A collection of microorganisms where cells stick to each other on a surface.

[[Category:Microbiology]]
[[Category:Cell biology]]
[[Category:Bacteriology]]
[[Category:Archaea]]

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