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: Composed of a phospholipid bilayer with embedded proteins, carbohydrates, and cholesterol.
- Fluidity: Phospholipids and proteins move laterally, allowing flexibility and self-healing.
- Mosaic Nature: The membrane contains diverse proteins that serve various functions.
2. Functions of Membrane Proteins
- Transport: Move substances via channels and carriers.
- Enzymatic Activity: Catalyze reactions at the membrane surface.
- Signal Transduction: Relay messages from the external to internal environment.
- Cell-Cell Recognition: Identify and communicate with other cells.
- Intercellular Joining: Link adjacent cells together.
- Attachment to Cytoskeleton and ECM: Anchor the membrane and help maintain shape.
3. Selective Permeability
- Permeable to: Small nonpolar molecules (e.g., O₂, CO₂) and small polar molecules (e.g., H₂O).
- Impermeable to: Large polar molecules and ions, which require transport proteins.
In a Nutshell
- The fluid mosaic model explains the membrane’s dynamic and flexible nature.
- Membrane proteins are essential for transport, communication, and structural roles.
- Selective permeability is key to maintaining a stable internal cellular environment.