Lecture Notes: Transport Across Membranes

Introduksyon

• Ika-6 na linggo ng quarter 1
• Topic: Transport Across Membranes
• Mga Competencies:
  • Ipaliwanag ang iba't-ibang transport mechanisms ng mga cells
  • I-differentiate ang endocytosis sa exocytosis

Review ng Nakaraang Lesson

• Cell Membrane Structure: Fluid mosaic model
• Molecules in Membrane: Phospholipid bilayer, proteins, carbohydrates, cholesterol
• Functions ng Cell Membrane:
  • Protection and shape
  • Compartmentalization
  • Recognition of molecules
  • Transport mechanisms

Featured Scientists of the Week

• James Rothman, Randy Schekman, Thomas Sudhof (Nobel Prize in Physiology and Medicine, 2013)
• Contribution: Vesicular transport (exocytosis and endocytosis)

Main Topic: Membrane Transport

• Definition: Movement of particles across a membranous barrier
• Importance: Absorption of nutrients, discharge of waste materials
• Types of Materials:
  1. Small hydrophobic molecules (e.g., Oxygen, CO2)
  2. Small uncharged polar molecules (e.g., Water, urea, glycerol)
  3. Large uncharged polar molecules (e.g., Glucose, sucrose)
  4. Ions (e.g., Na+, K+)

Factors Affecting Membrane Transport

1. Membrane Permeability: Heat, pH, lipid bilayer packing
2. Size and Charge of Solute: Larger and more charged = harder to transport
3. Transmembrane Solute Concentration: Higher concentration gradient = faster transport

Types of Membrane Transport

Passive Transport

• Definition: No energy required; driven by kinetic energy/concentration gradient
• Types:
  • Simple Diffusion: Direct passage through membrane (e.g., gas exchange in alveoli)
  • Osmosis: Diffusion of water (e.g., food preservation, osmoregulation in fish)
  • Facilitated Diffusion: Movement through a protein channel (e.g., glucose transport)

Active Transport

• Definition: Requires energy (ATP); moves substances against the concentration gradient
• Types:
  • Primary Active Transport: Direct use of ATP (e.g., sodium-potassium pump)
  • Secondary Active Transport: Uses electrochemical potential difference (e.g., co-transport)
  • Bulk Transport: Movement of large materials via vesicles (e.g., endocytosis, exocytosis)

Detailed Mechanisms

Passive Transport

• Simple Diffusion: Movement of small molecules directly through membrane
  • Example: Gas exchange in alveoli
• Osmosis: Movement of water through a selectively permeable membrane
  • Hypertonic: Solution has higher solute concentration
  • Hypotonic: Solution has lower solute concentration
  • Isotonic: Equal solute concentration
• Facilitated Diffusion: Movement through protein channels or carriers
  • Channel Proteins: Form pores (e.g., aquaporins for water)
  • Gated Channel Proteins: Open/close in response to stimulus
  • Carrier Proteins: Change shape to transport molecules (e.g., glucose)

Active Transport

• Primary Active Transport: Uses ATP directly
  • Example: Sodium-potassium pump
• Secondary Active Transport: Uses potential energy from electrochemical gradient
  • Symporter: Moves two molecules in the same direction
  • Antiporter: Moves two molecules in opposite directions
• Bulk Transport: Includes endocytosis and exocytosis
  • Endocytosis: Taking in substances (e.g., phagocytosis, pinocytosis, receptor-mediated endocytosis)
  • Exocytosis: Releasing substances outside the cell

Assessment Questions

1. Which is not true about active transport?
2. What type of transport is represented? (Image-based)
3. Which type of transport moves molecules from an area of high concentration to low concentration?
4. In which direction will water move? (Image-based)
5. Which molecules can be transported through passive movement?

Conclusion

• Review key points on membrane transport
• Encourage feedback from students
• Reminder for next week's lesson