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Anatomy & Physiology: Cell Junctions, Membrane Transport, and Membrane Potential

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  • What are the three main types of cell junctions?
    Tight junctions, desmosomes, and gap junctions.
  • What is the primary function of tight junctions?
    Tight junctions create leakproof seals between cells, preventing fluids and molecules from passing between them.
  • Where are tight junctions especially useful in the body?
    In organs that must be leakproof, such as the urinary bladder.
  • How do desmosomes function in cell adhesion?
    Desmosomes act like Velcro, attaching cells tightly but allowing flexibility under stress.
  • What proteins form the linker in desmosomes?
    Linker proteins called cadherins interlock like zipper teeth between neighboring cells.
  • What is the role of keratin filaments in desmosomes?
    Keratin filaments connect plaques inside cells, providing anchoring strength.
  • What is the main function of gap junctions?
    Gap junctions allow direct communication between cells by passing ions, hormones, and nutrients.
  • What proteins form the tunnels in gap junctions?
    Transmembrane proteins called connexons form the channels.
  • What is the structure of the plasma membrane?
    A phospholipid bilayer with polar heads facing outward and hydrophobic tails inward, embedded with proteins and cholesterol.
  • What does it mean that membranes are 'fluid mosaics'?
    Proteins (the mosaic) move within the fluid phospholipid bilayer (the grout), allowing membrane flexibility.
  • Name the three major categories of membrane proteins.
    Transport proteins, receptor proteins, and recognition proteins.
  • What is passive transport?
    Movement of molecules across membranes without energy, driven by diffusion down a concentration gradient.
  • What are the types of passive transport?
    Simple diffusion, facilitated diffusion, and osmosis.
  • What is osmosis?
    The diffusion of water across a selectively permeable membrane.
  • Define isotonic, hypertonic, and hypotonic solutions in relation to red blood cells.
    Isotonic: equal water movement; Hypertonic: water moves out, cells shrink; Hypotonic: water moves in, cells swell.
  • What factors influence the speed of diffusion?
    Concentration gradient, molecular size, and temperature.
  • What is active transport?
    Movement of molecules across membranes requiring energy (ATP), often against concentration gradients.
  • What are the two types of active transport?
    Primary active transport uses ATP directly; secondary active transport uses energy from ionic gradients.
  • Describe the sodium-potassium pump.
    An antiporter that pumps Na+ out and K+ into the cell against their gradients, maintaining electrochemical balance.
  • What is vesicular transport?
    Transport of large particles or fluids across membranes in vesicles, requiring ATP.
  • Name the types of vesicular transport.
    Endocytosis, exocytosis, transcytosis, and vesicular trafficking.
  • What is phagocytosis?
    A type of endocytosis where cells engulf large particles or microorganisms ('cell eating').
  • What is pinocytosis?
    A type of endocytosis where cells ingest extracellular fluid and dissolved substances ('cell drinking').
  • What is receptor-mediated endocytosis?
    Selective uptake of molecules via receptors that cluster in coated pits forming vesicles.
  • What is resting membrane potential (RMP)?
    The electrical potential across the plasma membrane due to separation of charged particles.
  • Which ion primarily sets the resting membrane potential?
    Potassium (K+) because of its diffusion out of the cell and electrical gradient.
  • How does K+ contribute to RMP?
    K+ diffuses out through leakage channels but is pulled back by negative interior charge, balancing at RMP.
  • How does sodium (Na+) affect RMP?
    Na+ is attracted inside but membrane permeability to Na+ is low, so it has less influence than K+.
  • What role does the glycocalyx play in cell-environment interactions?
    It mediates cell adhesion and communication via cell adhesion molecules (CAMs) and membrane receptors.