Overview
This lecture covers the structure of the plasma membrane, its components, and how its properties affect cell function and drug administration.
Plasma Membrane Functions
- Separates the cell’s interior from the external environment, maintaining homeostasis.
- Provides structural support and assists in cell communication and identification.
Key Components of the Plasma Membrane
- Composed of a phospholipid bilayer with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
- Phospholipids arrange so that hydrophobic tails face inward and hydrophilic heads face outward toward watery environments.
- Contains proteins (integral and peripheral), glycoproteins, glycolipids, and cholesterol.
Fluidity and Structure
- The membrane is fluid and dynamic, allowing components to move and change.
- Cholesterol provides membrane rigidity and stability; more cholesterol increases rigidity.
- Proteins and other molecules can be added or removed based on cell needs.
Membrane Permeability
- Hydrophobic or very small molecules (like gases or lipid-soluble drugs) can cross the membrane easily.
- Hydrophilic or polar molecules need help from protein channels or carriers to cross the membrane.
- The membrane's permeability determines what substances can enter or leave the cell.
Membrane Proteins
- Integral proteins span the membrane and function as channels, carriers, or receptors.
- Peripheral proteins are attached to the membrane surface and aid in communication or attachment.
- Proteins can also be enzymes, structural supports, or signaling molecules.
- Glycoproteins and glycolipids are important for cell recognition and signaling.
Clinical Application: Drug Delivery
- Lipid-soluble (hydrophobic) drugs can be absorbed through the skin (e.g., steroid creams).
- Water-soluble (hydrophilic) drugs cannot cross the membrane via the skin and must be injected.
Key Terms & Definitions
- Plasma membrane — the dynamic boundary that separates the cell interior from the outside.
- Phospholipid bilayer — double layer of phospholipids forming the membrane structure.
- Hydrophilic — attracted to water; describes the phospholipid heads.
- Hydrophobic — repelled by water; describes the phospholipid tails.
- Integral proteins — proteins embedded throughout the membrane.
- Peripheral proteins — proteins attached to only one surface of the membrane.
- Glycolipid/Glycoprotein — lipid/protein with attached sugar molecules used for recognition.
- Cholesterol — lipid molecule that adds rigidity to the membrane.
- ICF (Intracellular Fluid) — fluid inside the cell (cytosol).
- ECF (Extracellular Fluid) — fluid outside the cell.
Action Items / Next Steps
- Review the relationship between membrane structure and drug delivery methods.
- Prepare for the next lecture on cell membrane transport mechanisms.