Membrane Dynamics Lecture

Key Objectives

• Understand the difference between transport systems.
• Identify different types of passive and active transport and their characteristics.
• Distinguish between endocytosis and exocytosis.
• Distinguish between ligand-gated and voltage-gated channels.
• Understand uniport, symport, and antiport mechanisms.
• Differentiate between hypotonic, isotonic, and hypertonic solutions.

Transport Systems

Types of Transport

• Passive Transport: No energy required, solute moves down the concentration gradient.
• Active Transport: Requires energy, solute moves against the concentration gradient.
  • Primary Active Transport: Uses ATP.
  • Secondary Active Transport: Uses energy indirectly.
• Vesicular Transport: Includes endocytosis and exocytosis.

Passive Transport

• Diffusion: Solute moves from high to low concentration.
  • Types of diffusion:
    • Lipid (Simple) Diffusion: Solute moves through the lipid membrane without assistance.
    • Channel Diffusion: Uses channel proteins; can be gated or non-gated.
    • Facilitated Diffusion: Uses carrier proteins, changes shape to transport solute.
• Osmosis: Movement of water towards higher solute concentration.

Types of Channels

• Non-Gated Channels: Always open; primarily for water.
• Gated Channels: Open/close controlled by signals (ligand or voltage).
  • Ligand-Gated Channels: Open when a ligand (e.g. hormone, neurotransmitter) binds.
  • Voltage-Gated Channels: Open in response to changes in membrane potential.

Tonicity

• Hypotonic: Lower solute concentration compared to another solution.
• Isotonic: Equal solute concentration compared to another solution.
• Hypertonic: Higher solute concentration compared to another solution.

Effects on Cells

• Hypertonic Solution: Cells shrink as water leaves.
• Isotonic Solution: No change in cell size.
• Hypotonic Solution: Cells swell as water enters.

Active Transport

• Solute moves from low to high concentration, requires energy.
• Primary Active Transport: Utilizes ATP directly.
  • Example: Sodium-potassium pump.
• Secondary Active Transport: Relies on energy from another solute moving down its gradient.

Membrane Transport Proteins

• Uniport: Transports one type of solute.
• Symport: Transports two solutes in the same direction.
• Antiport: Transports two solutes in opposite directions.

Vesicular Transport

• Exocytosis: Material exits the cell.
• Endocytosis: Material enters the cell.

Body Water Compartments

• Intracellular Fluid (ICF): Inside cells, high in potassium.
• Extracellular Fluid (ECF): Outside cells, high in sodium.
  • Interstitial Fluid: Between cells.
  • Plasma: In blood vessels.

Summary

• Different transport mechanisms are crucial for maintaining cellular homeostasis and function.
• Understanding the dynamics of membrane transport is essential for understanding physiological processes.