Part I: Structural aspect_Membrane_2025_2026_ English

Ultrastructural Aspects of the Plasma Membrane: Part I

At the ultrastructural level, observed by transmission electron microscopy, the plasma membrane appears as a trilaminar structure approximately 7–10 nm thick. It is composed of two electron-dense layers separated by a lighter central layer, corresponding to the phospholipid bilayer. Embedded within this bilayer are integral and peripheral proteins, which contribute to membrane transport, signaling, and cell recognition. The outer surface may display a glycocalyx, formed by carbohydrate chains attached to lipids and proteins, especially in epithelial cells. The plasma membrane shows asymmetry between its inner and outer leaflets and is not a rigid structure; instead, it exhibits fluidity, allowing lateral movement of lipids and proteins, in accordance with the fluid mosaic model.