JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD Pharm. D I Year MEDICIAL BIOCHEMISTRY Previous Question Paper (January - 2022 - R08)

Transport across cell membranes is essential for maintaining homeostasis, nutrient uptake, and waste removal. These processes are categorized based on energy requirements and the use of membrane proteins.

1. Passive Transport: This process occurs along the concentration gradient (from high to low concentration) and does not require metabolic energy (ATP).

• Simple Diffusion: Small, non-polar molecules like O₂, CO₂, and lipid-soluble substances move directly through the phospholipid bilayer.
• Facilitated Diffusion: Polar molecules (e.g., glucose, amino acids) and ions move across the membrane via specific integral membrane proteins, such as channel proteins or carrier proteins, without energy expenditure.
• Osmosis: The passive movement of water molecules across a semi-permeable membrane from a region of lower solute concentration to higher solute concentration.

2. Active Transport: This process moves substances against their concentration gradient (from low to high concentration), requiring ATP and specific carrier proteins.

• Primary Active Transport: ATP is directly hydrolyzed to provide energy for transport. A classic example is the Na⁺/K⁺-ATPase pump, which maintains the electrochemical gradient by pumping three Na⁺ ions out of the cell and two K⁺ ions into the cell.
• Secondary Active Transport (Co-transport): This utilizes the electrochemical gradient created by primary active transport. The movement of one molecule down its gradient provides the energy to move another molecule against its gradient. This includes symport (same direction) and antiport (opposite direction) mechanisms.

3. Vesicular Transport: This involves the movement of large molecules or bulk materials via membrane-bound vesicles.

• Endocytosis: The cell membrane invaginates to engulf extracellular material, forming a vesicle. This includes phagocytosis (cell eating) and pinocytosis (cell drinking).
• Exocytosis: Intracellular vesicles fuse with the plasma membrane to release their contents into the extracellular space, a process vital for neurotransmitter release and hormone secretion.