CELL ENVELOPE Meaning and
Definition
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The term "cell envelope" refers to the outermost protective layer surrounding a cell, primarily found in prokaryotic organisms such as bacteria and archaea. It consists of a combination of various structures that act as a barrier, shielding the cell from external threats while maintaining its structural integrity.
The cell envelope typically comprises three layers: the outer membrane, the cell wall, and the inner or plasma membrane. The outer membrane is exclusive to gram-negative bacteria and is composed of lipopolysaccharides and proteins. It acts as a selective permeability barrier, preventing the entry of harmful substances into the cell.
Beneath the outer membrane lies the cell wall, which provides structural support for the cell. It is made up of peptidoglycan, a mesh-like polymer of sugars and amino acids that imparts rigidity to the bacterial cell. The presence of peptidoglycan also contributes to the characteristic staining properties used to differentiate between gram-positive and gram-negative bacteria.
Finally, the inner membrane or plasma membrane functions as a semi-permeable barrier, controlling the movement of nutrients, waste products, and other molecules in and out of the cell. It plays a crucial role in cellular respiration and the synthesis of macromolecules. Additionally, the inner membrane often contains various proteins and transport systems responsible for crucial functions like energy production and signal transduction.
Overall, the cell envelope serves as a protective shield, regulating the flow of substances and maintaining the structural integrity of the cell, thereby ensuring its survival and functionality.
Etymology of CELL ENVELOPE
The etymology of the word "cell envelope" comes from the combination of two distinct terms: "cell" and "envelope".
The term "cell" originated from the Latin word "cellula", meaning small room or cell. It was initially used in the context of monastic cells and later extended to describe biological cells in the late 17th century.
The term "envelope" also has Latin roots, derived from "envelopare", meaning to wrap or cover. It entered the English language in the 17th century, describing a covering or casing around an object.
When the two terms are combined, "cell envelope" essentially refers to the outermost layer or protective covering of a cell. It is commonly used in microbiology to describe the complex structure that surrounds and protects the bacterial cell.
