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Chapter 5: Membrane Transport and Cell Signaling

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Termini in questo insieme (29)

  • Fluid mosaic model
    Describes the plasma membrane as a dynamic structure with proteins and lipids forming specialized patches that move laterally within the phospholipid bilayer.
  • Phospholipid bilayer structure
    Composed of amphipathic phospholipids with hydrophilic heads facing water and hydrophobic tails shielded inside, forming a stable boundary between aqueous compartments.
  • Membrane fluidity factors
    Unsaturated hydrocarbon tails increase fluidity by preventing tight packing; cholesterol stabilizes fluidity by restraining movement at high temperatures and preventing solidification at low temperatures.
  • Integral vs. peripheral membrane proteins
    Integral proteins span the lipid bilayer and often form hydrophilic channels; peripheral proteins are loosely attached to membrane surfaces, often on the cytoplasmic side.
  • Selective permeability of membranes
    Membranes allow some substances to cross more easily than others, with hydrophobic molecules passing rapidly and ions or polar molecules requiring transport proteins.
  • Passive transport
    Diffusion of substances down their concentration gradient across membranes without energy input, including simple diffusion and facilitated diffusion via transport proteins.
  • Facilitated diffusion
    Passive transport aided by channel or carrier proteins that allow specific polar molecules or ions to cross membranes faster than by diffusion alone.
  • Active transport
    Energy-requiring process where transport proteins move solutes against their concentration gradients, often powered by ATP hydrolysis.
  • Sodium-potassium pump cycle
    Moves 3 Na+ ions out and 2 K+ ions in per cycle using ATP; involves binding, phosphorylation, conformational change, ion release, and dephosphorylation.
  • Osmosis
    Diffusion of free water across a selectively permeable membrane from higher free water concentration (lower solute) to lower free water concentration (higher solute).
  • Tonicity effects on cells
    Isotonic: no net water movement; hypotonic: water enters cell causing swelling; hypertonic: water leaves cell causing shrinkage or plasmolysis.
  • Bulk transport mechanisms
    Exocytosis secretes large molecules via vesicle fusion with plasma membrane; endocytosis takes in large molecules by vesicle formation (phagocytosis, pinocytosis, receptor-mediated).
  • G protein-coupled receptors (GPCRs)
    Transmembrane receptors that activate G proteins upon ligand binding, triggering intracellular signaling cascades.
  • Ligand-gated ion channels
    Membrane receptors that open or close ion channels in response to ligand binding, altering ion flow and cellular activity.
  • Intracellular receptors
    Receptors located in cytoplasm or nucleus that bind hydrophobic signaling molecules able to cross the membrane, often acting as transcription factors.
  • Phosphorylation cascade
    Series of protein kinases activating each other by phosphorylation, amplifying the signal and regulating cellular responses.
  • Second messengers
    Small nonprotein molecules like cyclic AMP (cAMP) that diffuse within the cell to propagate and amplify signals.
  • Cotransport
    Transport protein couples downhill diffusion of one solute to uphill transport of another, using energy stored in electrochemical gradients.
  • Membrane potential
    Voltage across the plasma membrane caused by unequal ion distribution, influencing ion movement and cellular processes.
  • Role of cholesterol in membranes
    Cholesterol modulates membrane fluidity by restraining phospholipid movement at high temperatures and preventing tight packing at low temperatures.
  • Aquaporins
    Channel proteins that facilitate rapid water transport across membranes, excluding charged ions like hydronium.
  • Endocytosis types
    Phagocytosis engulfs particles; pinocytosis ingests extracellular fluid nonspecifically; receptor-mediated endocytosis selectively internalizes specific molecules.
  • Cell-cell recognition
    Cells recognize each other via membrane carbohydrates attached to glycoproteins and glycolipids, important for immune response and development.
  • Membrane synthesis and sidedness
    Membrane proteins and lipids are synthesized in the ER and Golgi, establishing asymmetric distribution of molecules between inner and outer membrane faces.
  • Signal transduction stages
    Reception: ligand binds receptor; transduction: signal relayed and amplified; response: cellular activity changes such as gene expression or enzyme activation.
  • Role of protein kinases and phosphatases
    Protein kinases add phosphate groups to activate proteins; phosphatases remove them to deactivate proteins, regulating signaling pathways.
  • Membrane protein functions
    Include transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton and ECM.
  • Electrogenic pumps
    Membrane proteins like sodium-potassium and proton pumps that generate voltage by moving ions, storing energy for cellular work.
  • Receptor-mediated endocytosis example
    Cells take in cholesterol via LDL receptors; defects cause familial hypercholesterolemia with high blood cholesterol.