Fluid Mosaic Model: Study Notes

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Fluid Mosaic Model

Definition: The Fluid Mosaic Model is a scientific concept that describes the structure of cell membranes. It was proposed by S.J. Singer and Garth Nicolson in 1972.

Key Features:

• • Phospholipid Bilayer:The cell membrane is primarily composed of a double layer of phospholipids.
  • Phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
  • The hydrophilic heads face outward towards the water inside and outside the cell, while the hydrophobic tails face inward, away from water, forming a barrier.
  • Proteins:The membrane is embedded with proteins that float in or on the fluid lipid bilayer.
  • Integral Proteins: These span the entire membrane and are involved in transport, acting as channels or carriers.
  • Peripheral Proteins: These are attached to the outer or inner surface of the membrane and are involved in signaling or structural support.
  • Carbohydrates:Carbohydrates are attached to proteins (glycoproteins) or lipids (glycolipids) on the extracellular surface of the membrane.
  • These carbohydrate chains serve as recognition sites for cell-cell interactions and communication.
  • Cholesterol:Cholesterol molecules are interspersed within the phospholipid bilayer.
  • They help stabilize the membrane's fluidity, making it less permeable to very small water-soluble molecules that might otherwise pass freely through.

Fluidity:

• The membrane is described as "fluid" because the lipids and proteins can move laterally within the layer, much like icebergs floating in the sea.
• This fluidity is essential for the functioning of the membrane, allowing it to be flexible, self-sealing, and capable of fusing with other membranes.

Mosaic:

• The "mosaic" part of the model refers to the pattern produced by the scattered protein molecules when the membrane is viewed from above.

Functions of the Fluid Mosaic Model:

• Selective Permeability: The membrane controls the movement of substances into and out of the cell.
• Transport: Proteins act as channels or carriers for molecules to move across the membrane.
• Cell Signaling: Receptors on the membrane surface interact with external signals (hormones, neurotransmitters).
• Cell Recognition: Carbohydrate chains enable the cell to recognize and be recognized by other cells.

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