Cell Membrane Structure and Function

Cell Membrane Structure and Function

• The cell membrane is composed of lipids and proteins, separating the cell's contents from the outside world.
• It's a bilayer, meaning it consists of two layers of phospholipids.
• Phospholipids have hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
• The heads face the watery environment, while the tails face away from it, forming a barrier.
• The Fluid Mosaic Model more accurately depicts the structure of the cell membrane.
• It's called "fluid" because the cell membrane isn't rigid, and "mosaic" because of the various proteins embedded in the lipid bilayer.
• Proteins within the membrane can help with transport.

Membrane Transport

• Semipermeable: The cell membrane allows some substances to pass through while blocking others.
• Diffusion: The movement of liquid or gas molecules from a high concentration area to a low concentration area, across a semipermeable membrane.
• Osmosis: The diffusion of water across a semipermeable membrane, influenced by solute concentrations.
• Hypertonic solution: A solution with a higher solute concentration outside the cell than inside. Water moves out of the cell, causing it to shrink.
• Hypotonic solution: A solution with a lower solute concentration outside the cell than inside. Water moves into the cell, causing it to swell and potentially burst.
• Isotonic solution: A solution with an equal solute concentration inside and outside the cell. Water moves in and out of the cell at an equal rate, maintaining the cell's shape.

Types of Membrane Transport

• Facilitated Diffusion: Movement of molecules across the membrane with the help of carrier proteins, without energy input.
• Active Transport: Movement of molecules against the concentration gradient, requiring energy (like ATP).
• Bulk Transport: Large molecules are moved across the membrane.
  • Exocytosis: Substances are released out of the cell.
  • Endocytosis: Substances are taken into the cell.
  • Receptor-mediated endocytosis: A specific type of endocytosis where molecules bind to specific receptors on the cell surface before being taken into the cell.