2._Cell_Membrane___Diffusion_Presentation

Cell Membrane & Diffusion

• Osmosis: A type of passive transport allowing substances to move across cell membranes without energy.

• Passive transport is essential for cellular processes.

Objectives

• Course Objective #4: Distinguish between types of passive and active transport mechanisms in cell membranes.

• Review Topics:

  • Structure and properties of the cell membrane

  • Semipermeable and fluid-mosaic model

  • Biomolecules present in the cell membrane

  • Mechanisms of diffusion and osmosis

  • Case study: "The Case of the Exploding Fish"

Key Knowledge Check Questions

1. Name three differences between prokaryotic and eukaryotic cells.

2. Name three differences between plant and animal cells.

3. Identify three organelles enclosed by double membranes.

The Cell Membrane

• Structure:

  • Hydrophilic head and hydrophobic tail in phospholipids.

  • Composed of a phospholipid bilayer which is essential for cell functionality.

  • Includes glycoproteins, cholesterol, and cytoskeleton elements.

Phospholipid Bilayer

• Amphipathic nature: Phospholipids possess both hydrophilic heads and hydrophobic tails.

• Arranged in two layers with heads facing outward, forming a barrier that regulates permeability.

Fluid Mosaic Model

• Compares to icebergs drifting in the sea.

• Fluid: Components can move laterally within the membrane.

• Mosaic: Made up of various components like proteins and lipids maintaining barrier integrity.

Role of Cholesterol

• Stability: It stabilizes membrane fluidity by:

  • Decreasing fluidity at high temperatures.

  • Preventing tight packing at low temperatures.

Protein Functions in Membranes

• Proteins perform various functions:

  • Transport

  • Enzymatic Activity

  • Adhesion

  • Receptor Functions

Membrane Structure

• Transmembrane Proteins: Amphipathic with hydrophilic and hydrophobic regions.

• Peripheral Membrane Proteins: Mostly hydrophilic.

Cell Membrane Properties

• Acts as a barrier separating different chemical environments inside and outside the cell.

• Semipermeable: Allows selective permeability; small uncharged molecules can cross, large or charged molecules cannot.

Diffusion and Osmosis

• Diffusion: Movement of substances from high to low concentration.

  • Equilibrium achieved when concentrations equalize.

• Osmosis: Specific type of diffusion concerning water movement across a semipermeable membrane to balance concentrations.

Cellular Behavior in Different Solutions

• Introduction to the case study of hemolysis in animal cells indicating the effects of osmotic pressure.

  • Freshwater fish face challenges due to their environment but have mechanisms (kidneys) to regulate water balance.

• Concentration Differences:

  • Water moves to where solute concentrations are higher to achieve equilibrium.

Why Don't Fish Explode?

• Fish do not explode due to their adaptation and kidney function:

  • Active uptake of ions keeps internal environments balanced.

  • They manage water loss by controlling internal urea levels.

Osmoregulation in Different Environments

• Saltwater Fish: Lose water continuously but manage it through diet and waste elimination strategies.

• Euryhaline Animals: Adapt to changing environments, like crabs and fish moving from freshwater to saltwater, altering their osmotic strategies accordingly.

Conclusion

• Why Humans Don't Explode in Water: Humans have kidneys to excrete excess water and skin barriers to control water loss, offering more resilience against osmotic imbalances.