B2.1 Membrane SL

Membranes and Membrane Transport

Overview

  • Focus on how lipids and proteins create biological membranes.

  • Determine substance permeability across membranes.

Biological Membrane Models

  • Plasma membrane models exhibit fluidity for lipid-soluble molecule diffusion.

Key Concepts

Lipid Bilayers

  • Formation: Phospholipids naturally create bilayers in water.

  • Barriers: The hydrophobic core of membranes restricts large and hydrophilic molecules.

Membrane Transport Mechanisms

  1. Simple Diffusion

    • Movement of small molecules (e.g., O2, CO2) through phospholipid bilayer.

  2. Facilitated Diffusion

    • Channel Proteins: Allow specific ions to diffuse when open.

    • Carrier Proteins: Bind molecules and change shape to transport them.

  3. Active Transport

    • Pump Proteins: Use ATP to move substances against concentration gradient.

  4. Osmosis

    • Water movement across a semi-permeable membrane driven by solute concentration differences.

    • Aquaporins: Integral proteins that facilitate water movement.

Membrane Components

Membrane Proteins

  • Integral Proteins: Span the membrane; vital for transport and recognition.

  • Peripheral Proteins: Attached to surface; roles in signaling and support.

Glycoproteins and Glycolipids

  • Glycoproteins: Involved in cell recognition and adhesion.

  • Glycolipids: Help in immune response and cellular identity.

Fluid Mosaic Model

  • Describes the dynamic arrangement of lipids and proteins in the membrane.

    • Phospholipid bilayer is fluid, proteins can move laterally.

    • Evidence from biochemical techniques and fluorescent tagging.

Permeability Factors

  • Selective permeability influenced by size, charge, and polarity of substances.

  • Membranes can control solute passage using specific transport proteins.

Additional Concepts

Regulatory Aspects

  • Cell membranes maintain homeostasis through selective permeability and active transport systems.

Adaptation in Membrane Fluidity

  • Unsaturated fatty acids increase membrane fluidity in cold-adapted organisms.