Dentist Notes

Cell Membrane

General HistologyUpdated 1 min read
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Components

Membrane ComponentKey Characteristics & MCQ BuzzwordsPrimary Function in MCQs
Phospholipid BilayerAmphipathic matrix (hydrophilic heads outward, hydrophobic fatty acid tails inward).Forms the basic structural barrier; controls passive permeability of lipophilic substances.
CholesterolSteroid ring lipid wedged between hydrophobic phospholipid tails.Fluidity buffer (stabilizes membrane at high temperatures; prevents crystallization/freezing at low temperatures).
Integral (Transmembrane) ProteinsSpan the entire lipid bilayer; amphipathic.Act as channels, carriers, pumps (e.g., Na/K ATPase), and receptors for cell signaling.
Peripheral ProteinsAttached loosely to the inner or outer surface; easily removed.Cytoskeletal anchors (e.g., spectrin/ankyrin in RBCs) or intracellular signaling molecules.
GlycocalyxCarbohydrate coat (glycoproteins/glycolipids) on the outer leaflet only.Crucial for cell-cell recognition, adhesion, and acting as an immunological signature.
Lipid RaftsMicrodomains rich in sphingolipids and cholesterol; thicker and less fluid.Platforms for cell signaling and specialized endocytosis.

Top 3 Repeater MCQ Traps to Remember:

  1. Asymmetry: Carbohydrates (Glycocalyx) are never on the cytoplasmic side; they face the extracellular environment.
  2. Fluidity: The fluid nature is determined by the fatty acid tails (unsaturated = more fluid) but regulated/maintained dynamically by cholesterol.
  3. Transport Types:
    • Primary Active: Pumps (Na+/K+ pump, H+/K+ pump) that split ATP directly.
    • Secondary Active: Co-transporters (e.g., Na+ - glucose, Na+ - amino acids) that use the gradient built by a primary pump.