In-Depth Notes on Plasma Membranes and Membrane Permeability

Plasma Membranes and Membrane Composition

  • Key Components of Plasma Membrane
    • Phospholipids
    • Comprised of a hydrophilic head and hydrophobic tails
    • Forms a bilayer structure, with heads facing the aqueous environment and tails facing inward
  • Proteins in Membranes
    • Integral Proteins
    • Embedded in the lipid bilayer (also known as transmembrane proteins)
    • Amphipathic: possess both hydrophobic and hydrophilic regions
    • Peripheral Proteins
    • Loosely attached to the membrane surface

Membrane Structure

  • Fluid Mosaic Model
    • Fluid Nature: Membrane flexibility due to weak hydrophobic interactions
    • Affected by temperature:
      • Unsaturated fatty acid tails maintain fluidity at lower temperatures
      • Kinked structure prevents tight packing
    • Mosaic Nature: Comprised of various macromolecules (proteins, lipids, carbohydrates)
    • Cholesterol role:
      • Stabilizes membrane at high temperatures by reducing movement
      • Reduces phospholipid packing at low temperatures

Membrane Permeability

  • Selective Permeability
    • Ability to regulate what enters and exits the cell
    • Hydrophilic heads orient towards external or internal environments
    • Hydrophobic tails shield from aqueous environments

Membrane Carbohydrates

  • Glycolipids and Glycoproteins
    • Glycolipids: Carbohydrates bonded to lipids
    • Glycoproteins: Carbohydrates bonded to proteins
    • Essential for cell-to-cell recognition and communication

Plant Cell Structure

  • Cell Wall
    • Provides structure, protection, and regulates water intake
    • Composed mainly of cellulose, which makes it thicker than plasma membranes
    • Plasmodesmata: Channel-like structures connecting adjacent plant cells filled with cytosol

Adaptation to Environment: Case Study of Channichthyidae Fish

  • Adaptations in Low-Temperature Waters
    • Expected membrane lipid composition likely includes:
    • Higher proportions of unsaturated fatty acids to maintain fluidity
    • Increased cholesterol levels for structural stability in cold temperatures
    • Advantageous for survival includes preventing crystallization of membrane lipids and facilitating necessary physiological processes in extreme environments

Review/Practice Problems

  • Work on relevant questions from Unit 1 on phospholipid structure and review any practice problems regarding membrane compositions.
    • Be prepared to explain the implications of membrane fluidity and permeability on cellular function.