Lecture on Osmosis and Cell Membranes

Introduction

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Personal anecdote about improving an osmosis lab in the second year of teaching.

Osmosis: Water traveling through a semi-permeable membrane.
Egg lab: Soaking raw eggs in vinegar for 24-48 hours removes the shell, leaving the membrane intact.
The egg membrane mimics a cell membrane's function in osmosis scenarios.

A [body] cell can't be as large as a chicken egg due to surface area needs.
Surface area affects food entry, waste removal, and metabolic processes.
Smaller cells have a higher surface area to volume ratio (e.g., 6:1 in small models vs. 2:1 in larger models).
A higher ratio allows efficient cell processes and transport.

The cell membrane is present in all living cells (bacteria, protists, plants, animals, fungi, archaea).
Fluid Mosaic Model: Describes the cell membrane's structure.
- Mosaic: Many small pieces making a larger whole.
- Fluid: Components move around, aren't static.
Major components:
- Phospholipid Bilayer: Composed of phospholipids which are amphiphilic.
  - Polar heads (hydrophilic) love water; nonpolar tails (hydrophobic) avoid water.
  - Bilayer arrangement creates a barrier between inside and outside of cell.
- Cholesterol: Maintains membrane fluidity.
  - Acts as spacers in cold temperatures and connectors in warm temperatures.
- Proteins:
  - Peripheral Proteins: Located on the membrane's exterior, function as enzymes, attach to cytoskeleton.
  - Integral Proteins: Go through the membrane, involved in transport, e.g., glucose entry for ATP production.
  - Glycoproteins and Glycolipids: Involved in cell recognition and signaling.
  - Example: CD4 glycoprotein in immune cells, essential for activation and interaction, exploited by HIV.

Understanding cell membrane components and their roles is crucial for biology, disease treatment, and cellular processes research.
Encouragement to remain curious.