organellemembraner

Organelle membranes are lipid bilayers that enclose most eukaryotic organelles and, in the case of the cell, the plasma membrane. They establish distinct internal environments essential for metabolism and signaling. The membranes are dynamic and semi-permeable, regulating which substances enter or leave compartments.

Structure and composition: The core is a phospholipid bilayer with hydrophilic heads facing outward and hydrophobic tails inward. Cholesterol and specific lipids modulate fluidity and curvature. Membranes host integral and peripheral proteins that act as channels, transporters, receptors, and enzymes. The fluid mosaic model describes lateral mobility of components.

Major examples: Nuclear envelope consists of inner and outer membranes perforated by nuclear pores; Mitochondria have outer membrane and a highly folded inner membrane (cristae) housing respiratory enzymes; Chloroplasts possess double membranes and internal thylakoid membranes; Endomembrane system includes endoplasmic reticulum, Golgi apparatus, lysosomes, and vesicles. Each membrane hosts targeting sequences that direct proteins and lipids to its proper location.

Functions and dynamics: Membranes mediate selective transport via channels, transporters, pumps; generate electrochemical gradients; compartmentalize metabolic pathways; participate in signaling and membrane trafficking through vesicle formation and fusion. They are synthesized and remodeled by processes like vesicular trafficking, membrane fusion and fission, and membrane biogenesis in the ER and mitochondria.