WK4.10: Nutrient & Ion Transport

Introduction

  • Lecture on nutrient and iron transport by Dr. Hassan Chair.
  • Focus: transporter proteins, passive and active transport, membrane potential, vesicular transport (endocytosis and exocytosis).

Learning Outcomes

  • Explain mechanisms of molecular movement across membranes.
  • Describe membrane potential concepts.
  • Detail types of endocytosis and exocytosis.

Overview of Transport Mechanisms

  • Phospholipid Bilayer: Impermeable to most molecules, necessitating transport proteins.
  • Transporters: Facilitate molecule movement.
Types of Transport
  1. Passive Transport: Movement of molecules along concentration gradient without energy.
    • Facilitated Diffusion: Utilizes protein channels/carriers.
    • Osmosis: Movement of water across membranes.
  2. Active Transport: Movement against the concentration gradient, requiring energy (ATP).
    • Primary Active Transport: Direct usage of ATP.
    • Secondary Active Transport: Utilizes the gradient generated by primary transport.
  3. Vesicular Transport: Used for large molecules, includes endocytosis and exocytosis.

Facilitated Diffusion

  • Molecules move through channel proteins or carrier proteins.
  • Channel Proteins: Provide corridors for specific ions (e.g., sodium, potassium).
  • Carrier Proteins: Bind to molecules, change shape, and transport them (e.g., glucose transport in red blood cells via Glut1).
Types of Channels
  • Gated Channels: Open/close in response to stimuli (voltage-gated, ligand-gated).
  • Aquaporins: Specialized for water transport.

Active Transport

  • Active Transport Mechanism: Solutes pumped against concentration gradient.
  • Sodium-Potassium Pump: Transports 3 Na+ out and 2 K+ in, maintaining membrane potential.
  • Primary vs. Secondary Active Transport: Primary directly uses ATP; secondary uses gradients created by primary transport.
    • Secondary Transport Example: Sucrose uptake in plants driven by proton gradients.

Membrane Potential

  • Definition: Voltage difference across a membrane due to ion distribution.
  • Resting Membrane Potential: Maintained primarily by the sodium-potassium pump.
  • Higher K+ concentration inside the cell, while Na+ is higher outside.
  • Membrane potential is usually negative (between -50 to -200 mV).

Vesicular Transport

Exocytosis and Endocytosis
  • Exocytosis: Secretion of molecules via vesicles (e.g., insulin release by pancreas).
  • Endocytosis: Taking in substances, forming vesicles from membranes.
    • Types of Endocytosis:
    1. Pinocytosis: Non-specific uptake of fluids and small molecules (cellular drinking).
    2. Phagocytosis: Engulfing larger particles (cellular eating).
    3. Receptor-Mediated Endocytosis: Specific uptake mediated by receptor proteins.
  • Types of Exocytosis:
    1. Constitutive: Always active, releasing materials continuously.
    2. Regulated: Triggered by specific signals (e.g., hormones).
    3. Lysosomal: Involves waste removal by lysosomes.

Summary

  • Transport mechanisms are vital for nutrient and ion movement in cells.
  • Distinctions in transport type (passive vs. active, vesicular methods) are essential for cell function and energy management.
  • Understand these processes for upcoming examinations and the function of cellular activities.