Plazmamembraanin

Plazmamembraanin, also known as the cell membrane or plasma lemma, is a biological membrane that separates the interior of all cells from the outside environment. It is a selectively permeable barrier that controls the passage of substances into and out of the cell. The plasma membrane is composed primarily of a phospholipid bilayer, a double layer of phospholipid molecules. Each phospholipid molecule has a hydrophilic (water-attracting) head and a hydrophobic (water-repelling) tail. These molecules arrange themselves so that the hydrophilic heads face the aqueous environment both inside and outside the cell, while the hydrophobic tails are oriented towards the interior of the membrane.

Embedded within this lipid bilayer are various proteins. These proteins can be integral, spanning the entire membrane, or peripheral, attached to the surface. Membrane proteins serve a multitude of functions, including transport of molecules across the membrane, enzymatic activity, signal transduction, cell-cell recognition, and attachment to the cytoskeleton and extracellular matrix. Cholesterol molecules are also found interspersed within the phospholipid bilayer, contributing to membrane fluidity and stability. The plasma membrane is a dynamic structure, with its components constantly moving and interacting, allowing for essential cellular processes such as endocytosis and exocytosis, where the cell engulfs or expels substances by forming vesicles. Its structure and composition are crucial for maintaining cellular integrity and mediating interactions with the external environment.