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**Lipid Rafts** - **Definition**: Small, cholesterol and sphingolipid-rich areas within the plasma membrane. - **Function**: Act as platforms for key processes like cell signaling and movement. **Plasma Membrane** - **Main Functions**: Acts as a barrier, regulates molecule entr...

**Lipid Rafts** - **Definition**: Small, cholesterol and sphingolipid-rich areas within the plasma membrane. - **Function**: Act as platforms for key processes like cell signaling and movement. **Plasma Membrane** - **Main Functions**: Acts as a barrier, regulates molecule entry/exit, senses external signals, supports cell shape changes, and enables interactions between cells. - **Fluid Mosaic Model**: Membrane is not uniform; lipids and proteins move laterally but organize into specialized regions like lipid rafts. **Membrane Lipids** - **Phosphoglycerides**: Unsaturated and flexible, allow for fluidity. - **Sphingolipids**: Saturated, form more rigid and tightly packed regions. - **Cholesterol**: Adds stiffness, helps organize lipids into rafts by promoting phase separation. **Lipid Raft Functions** - **Signal Transduction**: Localizes receptors and proteins, making signaling more efficient. - **Cell Migration**: Provides platforms that help cells change shape and move, critical in immune responses. - **In Disease**: - **Cancer**: Cancer cells have more lipid rafts, which can reduce how easily certain drugs (like chemotherapy) pass through the membrane. - **Alzheimer's**: Lipid rafts play a role in the formation of amyloid plaques, which are linked to the progression of the disease. - **Prion Diseases**: Rafts help prion proteins (PrPC) interact with pathological forms (PrPSc), aiding their conversion and spread. **Research Methods** - **Detergent-Resistant Membrane Fractions**: Used to isolate and study raft components since they remain intact after detergent treatment. - **Cholesterol Depletion**: Cyclodextrins are used to selectively remove cholesterol, allowing scientists to observe how raft function changes. - **Microscopy**: Fluorescent imaging and atomic force microscopy are used to visualize lipid rafts and track their behavior in cells. **Unresolved Questions** - **Lipid Raft Size & Lifespan**: Exact dimensions and duration of rafts in the membrane are still uncertain and vary depending on the method used.