Overview
This lecture covers the structure and function of the cell membrane, emphasizing its selective permeability and the fluid mosaic model, as well as cell walls in various organisms.
Cell Membrane Structure
- The cell membrane surrounds the cell and regulates entry and exit of substances.
- It is described by the fluid mosaic model, meaning it is composed of many moving parts.
- Main components include phospholipids, proteins, cholesterol, glycoproteins, and glycolipids.
- Phospholipids form a bilayer with hydrophilic (water-loving) heads and hydrophobic (water-hating) tails.
- Cholesterol stabilizes the membrane, preventing it from drifting apart or becoming too rigid.
- Glycoproteins and glycolipids have attached sugars and function in cell signaling and recognition.
Selective Permeability
- Selective permeability means only certain substances can cross the membrane freely.
- Small, nonpolar molecules like oxygen and carbon dioxide move freely by diffusion.
- Large molecules or charged particles require proteins to cross the membrane.
- Channel proteins and aquaporins help specific molecules like water and glucose to pass.
- Active transport proteins, such as the sodium-potassium pump, move substances against their concentration gradients using energy (ATP).
Cell Wall Structure and Function
- Not all cells have cell walls; animals only have a cell membrane.
- Plant cell walls are made of cellulose, providing rigidity and protection.
- Bacterial cell walls are made of peptidoglycan and offer structural support.
- Fungal cell walls are composed of chitin.
- Cell walls give additional protection and regulate water intake.
Key Terms & Definitions
- Cell Membrane — A lipid bilayer that regulates the movement of substances in and out of the cell.
- Fluid Mosaic Model — Describes the cell membrane as a flexible layer with various moving molecules.
- Phospholipid — A molecule with a hydrophilic head and hydrophobic tail, forming the membrane bilayer.
- Selective Permeability — Ability of the membrane to allow certain molecules to pass while blocking others.
- Cholesterol — A lipid that maintains membrane stability and fluidity.
- Glycoprotein — A protein with attached sugars, involved in cell recognition.
- Glycolipid — A lipid with attached sugars, involved in signaling.
- Aquaporin — A protein channel that specifically allows water to cross the membrane.
- Cell Wall — A rigid layer outside the membrane in plants, bacteria, and fungi for support and protection.
Action Items / Next Steps
- Review the structure and function of the fluid mosaic model.
- Study differences in cell walls among plants, bacteria, and fungi.
- Prepare for a discussion or questions on selective permeability and transport proteins.