Rucete ✏ Campbell Biology In a Nutshell
Unit 2 THE CELL — Concept 7.1 Cellular membranes are fluid mosaics of lipids and proteins
Biological membranes are fundamental to cellular function, acting as selective barriers that regulate the passage of substances into and out of cells and organelles.
1. The Fluid Mosaic Model
Structure: Membranes are composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol, creating a dynamic and fluid structure.
Fluidity: The lateral movement of phospholipids and proteins within the layer allows for flexibility and self-healing.
Mosaic Nature: The diverse proteins embedded in or attached to the bilayer perform various functions, contributing to the 'mosaic' aspect.
2. Functions of Membrane Proteins
Transport: Facilitate the movement of substances across the membrane through channels and carriers.
Enzymatic Activity: Catalyze specific reactions at the membrane surface.
Signal Transduction: Transmit signals from the external environment to the cell's interior.
Cell-Cell Recognition: Enable cells to identify and interact with each other.
Intercellular Joining: Connect adjacent cells through junctions.
Attachment to the Cytoskeleton and ECM: Maintain cell shape and stabilize the membrane's location.
3. Selective Permeability
Permeable to: Small nonpolar molecules (e.g., O₂, CO₂) and, to a lesser extent, small polar molecules (e.g., H₂O).
Impermeable to: Large polar molecules and ions, requiring specific transport mechanisms.
In a Nutshell
The fluid mosaic model describes the dynamic and complex nature of cellular membranes.
Membrane proteins perform essential roles in transport, communication, and structural support.
Selective permeability ensures proper cellular function by regulating the internal environment.