Cell Membrane

The cell membrane or cell wall represents the outer boundary of a cell as a semipermeable membrane.

The cell membrane (the cells of humans and animals) consists of two layers of different lipids in which proteins are stored or attached. The stored proteins serve the directed and controlled selective passage of substances (ion channels, transport proteins) and the transmembrane transmission of extracellular signals (signal transduction). Many membrane proteins are receptor proteins, which have specific binding sites (receptors) for chemical signalling substances (hormones, neurotransmitters), which control the passage of substances through the receptors or perform the signalling function. The proteins attached to the Z. extra- or intracellularly either represent enzymes or they form an intracellular supporting structure as structural proteins.

The cell membrane (Membrana cellularis, cytomembrane) or peanale (lat. membrane), also called plasma membrane in plant cells, is a biomembrane that surrounds the living cell and maintains its inner environment. At a thickness of about 6-10 nm, it can be detected by light microscopy only as a vague line. Each cell identifies itself externally by means of its peripheral proteins (see antigen). These membrane proteins lie or ″schwimmen″ on or in the membrane. In addition, short-chain, partly tree-like branched carbohydrate compounds are often attached to the proteins and lipids on the outside of the cell membrane for labelling purposes. This is referred to as glycoproteins or glycolipids. The external structures of the cell membrane often have a receptor function. These glycoproteins and glycolipids also form glycocalyx, which provides stability in cells without cell walls. The outer side of the cell membrane is occupied by different receptors.

Die meisten Zellen besitzen ein Membranpotential, was heißt, dass zwischen innen und außen eine Potentialdifferenz besteht. Es entsteht durch unterschiedliche Stoff- und Ladungsverteilung ein elektrochemischer Gradient. Sonderbildungen sind bei tierischen Zellmembranen die Mikrovilli, Pseudopodien-artige Ausstülpungen nach außen, die die Oberfläche der Membran vergrößern und zusammen den ″Bürstensaum″ der Zelle bilden. Eine Zellmembran ist die Abgrenzung zwischen unterschiedlichen Zellen. Außerdem findet in der Zellmembran ein Stoffaustausch statt.

https://de.wikipedia.org/wiki/Zellmembran _{(Wikipedia CC-by-sa-3.0)}