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Anatomy & Physiology: Cell Structure and Membrane Transport Chapter 3

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Termini in questo insieme (20)

  • What are the three basic parts of a generalized human cell?
    Plasma membrane (flexible outer boundary), cytoplasm (intracellular fluid with organelles), and nucleus (DNA-containing control center).
  • Describe the structure of the plasma membrane.
    A double layer of phospholipids with embedded proteins, cholesterol for stiffness, forming a fluid mosaic model that controls entry and exit of substances.
  • What are the characteristics of phospholipids in the plasma membrane?
    Phosphate heads are polar and hydrophilic, fatty acid tails are nonpolar and hydrophobic, forming a bilayer with cholesterol increasing membrane stiffness.
  • What are the two main types of membrane proteins and their functions?
    Integral proteins span the membrane and act as transporters, enzymes, or receptors. Peripheral proteins attach loosely and function as enzymes, motor proteins, or cell connectors.
  • What is selective permeability of the plasma membrane?
    The membrane allows some substances to enter or exit while blocking others, maintaining internal cell environment by permitting nutrients in and wastes out.
  • Define simple diffusion and give examples of substances that use it.
    Movement of nonpolar, lipid-soluble molecules directly through the lipid bilayer, e.g., oxygen, carbon dioxide, steroid hormones, and small amounts of water.
  • What is facilitated diffusion and how does it differ from simple diffusion?
    Passive transport assisted by carrier or channel proteins for hydrophobic molecules like glucose, amino acids, and ions, moving down their concentration gradient.
  • Explain carrier-mediated facilitated diffusion.
    Specific large polar molecules bind to transmembrane carrier proteins, which change shape to transport the molecule across the membrane.
  • Describe channel-mediated facilitated diffusion.
    Molecules move through aqueous channels in transmembrane proteins, selective by pore size or charge; channels can be always open (leakage) or gated.
  • What is osmosis and how does it occur in cells?
    Movement of water through a selectively permeable membrane via lipid bilayer or aquaporins, from low to high solute concentration.
  • What is tonicity and its effect on red blood cells?
    Tonicity is a solution's ability to change cell shape by altering water volume: isotonic (normal), hypertonic (cell shrinks), hypotonic (cell swells and may burst).
  • What distinguishes active membrane transport from passive transport?
    Active transport requires energy (ATP) to move solutes against their concentration gradient, unlike passive transport which requires no energy.
  • Describe the sodium-potassium pump function.
    An ATPase enzyme pumps 3 Na+ out and 2 K+ into the cell, maintaining electrochemical gradients essential for muscle and nerve function.
  • What is secondary active transport?
    Uses energy stored in ion gradients created by primary active transport to drive movement of other solutes like sugars and amino acids.
  • What is vesicular transport and its types?
    Movement of large substances via membrane-bound vesicles; includes transcytosis, vesicular trafficking, endocytosis, and exocytosis.
  • Explain endocytosis and its three forms.
    Process of engulfing substances into the cell: phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (specific molecule uptake).
  • What is phagocytosis?
    Cell engulfs large particles by forming pseudopods, creating a phagosome that fuses with lysosomes for digestion; used by macrophages.
  • Describe pinocytosis.
    Nonspecific uptake of extracellular fluid and solutes by plasma membrane infolding, forming vesicles; main nutrient absorption method in intestines.
  • What is receptor-mediated endocytosis?
    Selective uptake where extracellular substances bind to specific receptors, concentrating molecules in protein-coated vesicles for internalization.
  • How does exocytosis work?
    Vesicles containing substances fuse with the plasma membrane, releasing contents outside the cell; triggered by signals and involves SNARE proteins.