Plasamamembraani

Plasmamembraani, also known as the cell membrane, is a biological membrane that separates the interior of all cells from the outside environment. It is composed of a lipid bilayer, primarily phospholipids, with embedded proteins. The lipid bilayer forms a selectively permeable barrier, controlling the passage of substances into and out of the cell. Phospholipids have a hydrophilic head and a hydrophobic tail. They arrange themselves into two layers with the hydrophobic tails facing inward and the hydrophilic heads facing outward, forming the basic structure of the membrane.

Proteins within the plasma membrane perform a variety of functions. Some act as channels or carriers, facilitating the transport of specific molecules across the membrane. Others serve as receptors, binding to signaling molecules and initiating cellular responses. Membrane proteins can also be involved in cell adhesion, cell-cell recognition, and enzymatic activity. Carbohydrates are often attached to proteins (glycoproteins) or lipids (glycolipids) on the outer surface of the plasma membrane, playing a role in cell recognition and immune responses.

The plasma membrane is a dynamic structure, with its components constantly moving and rearranging. This fluidity allows for essential cellular processes such as endocytosis and exocytosis, where the membrane engulfs or releases substances. The selective permeability of the plasma membrane is crucial for maintaining homeostasis, the stable internal environment of the cell. It regulates the concentration of ions, nutrients, and waste products, ensuring the cell can function properly.