membranile

Membranes are dynamic, lipid-based barriers that enclose cells and the compartments inside them. They regulate the passage of ions, nutrients, and signaling molecules, and provide an interface for communication with the surrounding environment. The most conspicuous example is the plasma membrane that surrounds the cell, while internal membranes delineate organelles such as the nucleus, mitochondria, and endoplasmic reticulum.

Biomembranes are primarily composed of a phospholipid bilayer, in which amphipathic phospholipid molecules arrange with hydrophobic tails inward and hydrophilic heads outward. Cholesterol modulates fluidity, and proteins are embedded or attached to the surface. The carbohydrate groups on the outer face contribute to cell recognition. The fluid mosaic model describes membranes as flexible, protein-containing bilayers with lateral diffusion of lipids and proteins.

Functions include forming a selective barrier, creating distinct internal environments, and enabling signaling and transport. Substances cross membranes by passive processes such as diffusion and facilitated diffusion, or by active transport that consumes energy. Cells also move material via vesicle transport, including endocytosis and exocytosis. Membrane potential, generated by ion gradients, powers electrical signaling in nerves and muscles.

Membranes vary by location and composition across organelles. Examples include the nuclear envelope, mitochondrial membranes, endoplasmic reticulum, Golgi membranes, lysosomes, and chloroplast membranes. In biotechnology, synthetic and biomimetic membranes enable filtration, dialysis, and biosensing, illustrating the broad relevance of membrane structure and function.