Overview
This lecture covers the structure and function of the plasma membrane in human cells, highlighting its composition, selective permeability, embedded molecules, and specialized membrane extensions.
Basic Structure of the Plasma Membrane
- The plasma membrane forms a barrier between the cell’s cytoplasm and the external environment.
- It is thin, flexible, and controls what enters or leaves the cell.
- The membrane is essential for maintaining the cell’s integrity and function.
Phospholipid Bilayer
- The main component is a bilayer of phospholipid molecules.
- Each phospholipid has a hydrophilic (water-loving) head and two hydrophobic (water-fearing) tails.
- Hydrophobic tails face inward, and hydrophilic heads face outward toward the cytoplasm and extracellular fluid.
- Small, hydrophobic molecules can pass through easily, but hydrophilic molecules need assistance.
Other Molecules in the Plasma Membrane
- Cholesterol molecules help the membrane maintain its shape and stability.
- Proteins serve as transport channels, receptors for signals, and cell-identity markers.
- Glycoproteins and glycolipids are also found in the membrane, aiding in cell recognition.
Plasma Membrane Extensions
- Flagella are whip-like extensions that help cells (like sperm) move.
- Cilia are hair-like extensions that move substances, such as mucus in airways.
- These extensions provide specialized functions depending on the cell type.
Importance of Cilia in Respiratory Health
- Cilia in the respiratory tract trap and remove dust and germs by moving mucus.
- Smoking or vaping paralyzes cilia, reducing their ability to clear airways, but their function can recover after quitting.
Key Terms & Definitions
- Cell — The smallest unit of life with a membrane, cytoplasm, and genetic material.
- Plasma Membrane — A semi-permeable lipid bilayer surrounding all cells.
- Cytoplasm — Jellylike material inside the cell membrane, containing organelles.
- Nucleus — Central organelle containing genetic material.
- Organelle — Tiny cellular structure performing specific functions.
- Phospholipid Bilayer — Two layers of phospholipids forming the cell membrane.
- Hydrophilic — Attracted to water.
- Hydrophobic — Repelled by water.
- Lipid — Water-insoluble substances, including fats and cholesterol.
- Protein — Macromolecules made of amino acids, essential for cell functions.
- Flagellum — Whip-like structure aiding cell movement.
- Cilium — Hairlike structure moving fluids along cell surfaces.
Action Items / Next Steps
- Review the functions and components of the plasma membrane.
- Study the differences between hydrophobic and hydrophilic molecules in relation to the membrane.
- Complete any assigned questions on membrane structure and function.