Chapter 5: Cell Membrane Composition and Function
Functions of the Plasma Membrane
- Acts as the outer border of cells and organelles
- Controls entry and exit of substances
- Receives external signals to trigger cellular responses
- Allows cell adhesion to neighboring cells (tight junctions, desmosomes, GAP junctions)
Structure of the Plasma Membrane
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Fluid Mosaic Model
- Composed of phospholipids, cholesterol, proteins, and carbohydrates
- Fluid due to lateral movement of components
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Phospholipid Bilayer
- Discovered with transmission electron microscopy in the 1950s
- Thickness: 5-10 nm
- Composition: 50% proteins, 40% lipids, 10% carbohydrates (varies by cell type)
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Phospholipids
- Amphipathic molecules with hydrophilic heads and hydrophobic tails
- Tail types: Saturated (solid) and unsaturated (fluid with kinks)
- Self-arrangement into bilayer sheets, liposomes, or micelles
Proteins in the Membrane
- Functions: Transport, receptors, enzymes, adhesion
- Types of Proteins
- Peripheral: Surface proteins
- Integral: Embedded through the bilayer (hydrophilic and hydrophobic regions)
Carbohydrates in the Membrane
- Oligosaccharides
- Attached to proteins (glycoproteins) or lipids (glycolipids)
- Important for cell recognition and attachment
- Blood types determined by glycoproteins on red blood cells
Importance and Regulation of Membrane Fluidity
- Factors Affecting Fluidity
- Phospholipid type: Saturated vs. unsaturated fatty acids
- Temperature: Warmer increases fluidity, colder decreases
- Cholesterol: Acts as a buffer for fluidity
Asymmetry of the Plasma Membrane
- Interior portion interacts with cytoskeleton
- Exterior portion interacts with extracellular matrix
- Selective Permeability
- Allows certain molecules to pass while maintaining differences between cytosol and extracellular environment
Transport Across the Membrane
- Passive Transport (to be discussed in next video)
- Active Transport
This concludes the first video of Chapter 5. The next video will discuss passive transport.