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Ch. 3 Cellular Transport and Membrane Physiology

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  • What distinguishes carrier proteins from channel proteins in membrane transport?
    Carrier proteins undergo conformational changes to transport molecules across the membrane, while channel proteins form open pores allowing passive flow.
  • What is facilitated diffusion?
    Passive movement of particles from high to low concentration across a membrane via protein channels or carrier proteins.
  • Name the three main cytoskeletal elements and their primary functions.
    Microtubules: hollow tubes for cell shape and transport; Microfilaments: actin strands for shape and movement; Intermediate filaments: rope-like fibers for mechanical strength.
  • What is the main cation inside cells (ICF) and outside cells (ECF)?
    Potassium (K⁺) is the main intracellular cation; Sodium (Na⁺) is the main extracellular cation.
  • List factors that increase the rate of diffusion according to Fick's Law.
    Increased temperature, smaller molecular size, larger surface area, greater concentration gradient, and solubility.
  • How do hydrophobic and hydrophilic molecules differ in membrane permeability?
    Hydrophobic (non-polar) molecules cross membranes more easily; Hydrophilic (polar or charged) molecules cross less easily.
  • What is osmosis?
    Passive movement of water down its concentration gradient through lipid bilayer or aquaporins toward higher solute concentration.
  • Define osmotic pressure.
    The pressure required to stop water movement by osmosis across a membrane.
  • What is the difference between osmolarity and tonicity?
    Osmolarity measures total solute concentration in a solution; tonicity compares solute concentration between a solution and a cell affecting cell volume.
  • Describe isotonic, hypertonic, and hypotonic solutions in relation to cells.
    Isotonic: no net water movement; Hypertonic: water leaves cell causing shrinkage; Hypotonic: water enters cell causing swelling.
  • What is the physiological saline concentration and its tonicity?
    0.9% NaCl, approximately 278–310 mOsM, is isosmotic and isotonic to human cells.
  • What is exocytosis?
    Active vesicular transport moving macromolecules out of the cell by vesicle fusion with the plasma membrane.
  • Name and define the three types of endocytosis.
    Phagocytosis: cell eating solids; Pinocytosis: cell drinking fluids; Receptor-mediated endocytosis: selective uptake via receptors.
  • What is primary active transport?
    Transport using ATP directly to move substances against their concentration gradient, e.g., Na+/K+ pump.
  • What is secondary active transport?
    Transport using energy indirectly from ATP by coupling movement of one molecule down its gradient to move another against its gradient.
  • Define uniport, symport, and antiport transporters.
    Uniport: one molecule one direction; Symport: two molecules same direction; Antiport: two molecules opposite directions.
  • How does the Na+/K+ ATPase pump function?
    Pumps 3 Na+ out and 2 K+ in per ATP hydrolyzed, maintaining ionic gradients and resting membrane potential.
  • What is the resting membrane potential and its typical value in neurons?
    The voltage difference across the membrane at rest, typically around \(-70\,mV\).
  • Why is the resting membrane potential negative inside the cell?
    Due to impermeable anionic proteins inside, higher K+ permeability causing positive charge to leave, and Na+/K+ pump activity.
  • What is an electrochemical gradient?
    A combined concentration and electrical gradient that influences ion movement across membranes.