Cell Transport Lecture Notes

Overview

• Cells exchange water, nutrients, and chemicals via their surrounding fluids.
• Key transport processes include:
  • Osmosis: movement of water through a semipermeable membrane.
  • Diffusion: general movement of particles from high to low concentration.
  • Active Transport: movement of substances against their concentration gradient.

Vocabulary

• ICF: Intracellular Fluid (inside the cell)
• ECF: Extracellular Fluid (outside the cell)
• Selectively Permeable: Allows selective passage via active transport, diffusion, and osmosis.
• Semi-permeable: Allows passage based on particle size.
• Permeant Solutes: Can cross membranes, irrelevant for tonicity.
• Impermeant Solutes: Cannot cross membranes, affect cell volume and tonicity.
• Crenate: Cell shrinking due to water loss via osmosis.
• Lysis: Cell bursting from excessive water intake (hemolysis for RBCs).
• Tonicity: Solution's ability to move water across a membrane.

Types of Solutions

• Isotonic: No net water movement; solute concentration equal inside and outside.
• Hypotonic: Water moves into the cell; solute concentration lower outside.
• Hypertonic: Water moves out of the cell; solute concentration higher outside.

Transport in Human Physiology

• Cell Membrane Function: Regulates substance movement in/out of the cell.
• Simple Diffusion: Substances move freely from high to low concentration.
• Facilitated Diffusion: Requires carrier or channel protein for movement with concentration gradient.
• Active Transport: Movement against concentration gradient using energy.

Things that Cannot Move Alone

• Hydrophilic or large substances: proteins, peptides, carbohydrates, nucleic acids, ions, triglycerides.

Things that Can Move Alone

• Small or hydrophobic substances: gases (O2, CO2), steroids, small alcohols, H2O (via aquaporins).

Active Transport Types

1. Primary Active Transport

   • Uses ATP directly to move ions against gradients.
   • Example: Na+/K+ pump creates ion gradients.

2. Secondary Active Transport

   • Uses ion concentration gradients as energy.
   • Example: Na+/glucose symporter uses Na+ gradient to move glucose.

How Primary & Secondary Transport Work Together

• Voltage and Current: Created by ion movement across membranes.
• Membrane Potential (Vm): Voltage across the membrane that can do work.

Membrane Proteins

• Channels: Passageways for hydrophilic/charged molecules; no energy use.
• Carriers: Bind and transport molecules either with or against gradients.
• Pumps: Use energy to move molecules against gradients (e.g., Na+/K+ pump).

Summary Table

| Membrane Protein | Direction of Molecules | Type of Transport | |------------------|------------------------|--------------------------| | Channel | Down gradient | Diffusion through channel| | Carrier | Down or against gradient| Facilitated or active transport| | Pump | Against gradient | Active transport |