Overview
This lecture explains the fluid mosaic model of cell membranes, focusing on the structure and function of the phospholipid bilayer and associated molecules.
Structure of the Cell Membrane
- The cell membrane separates the inside of the cell from the outside environment.
- It is primarily made of a phospholipid bilayer, forming a flexible and protective boundary.
- The phospholipid bilayer has hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward.
Phospholipids and Amphipathic Nature
- A phospholipid consists of a charged phosphate head (hydrophilic) and hydrocarbon tails (hydrophobic).
- Phospholipids are amphipathic, meaning they have both hydrophilic and hydrophobic parts.
- The amphipathic nature drives self-assembly into bilayers, forming the basic structure of membranes.
Membrane Proteins and Mosaic Nature
- Proteins are embedded in or attached to the membrane, contributing to its mosaic appearance.
- Transmembrane (integral) proteins span the bilayer; some only interact with one side.
- Peripheral proteins associate loosely with the membrane's surface.
Other Membrane Components
- Glycolipids (lipids with attached sugar chains) are involved in cell recognition and immune responses.
- Glycoproteins (proteins with attached sugar chains) also play roles in cell interactions and signaling.
- Cholesterol is interspersed within the bilayer, moderating fluidity and stability.
Fluidity of the Membrane
- The membrane is fluid, with phospholipids and proteins moving laterally, similar to oil’s consistency.
- Cholesterol helps maintain optimal fluidity, preventing the membrane from becoming too rigid or too fluid.
- The membrane's fluidity enables it to self-heal if disturbed.
Key Terms & Definitions
- Phospholipid — A molecule with a hydrophilic phosphate head and hydrophobic fatty acid tails.
- Bilayer — A double layer of molecules, like phospholipids, forming a barrier.
- Hydrophilic — Attracted to water.
- Hydrophobic — Repelled by water.
- Amphipathic — Having both hydrophilic and hydrophobic parts.
- Integral Protein — Embedded within the membrane, may span its entire width.
- Peripheral Protein — Attached to the membrane surface, not embedded.
- Glycolipid — Lipid with a carbohydrate chain attached, important for cell recognition.
- Glycoprotein — Protein with a carbohydrate chain attached, involved in signaling.
- Cholesterol — A lipid that stabilizes membrane fluidity.
Action Items / Next Steps
- Review diagrams of the fluid mosaic model and label all key components.
- Read about cell membrane functions and transport processes for next class.