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Cell Membrane Structure and Transport

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Termini in questo insieme (31)

  • Plasma membrane
    Separates the living cell from its environment and is selectively permeable, allowing only certain substances to cross.
  • Phospholipid bilayer
    Composed of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward, forming a barrier.
  • Amphipathic molecules
    Molecules that have both hydrophobic and hydrophilic components, like phospholipids.
  • Fluid mosaic model
    Describes the membrane as a fluid structure with a mosaic of proteins embedded within the phospholipid bilayer.
  • Membrane fluidity
    Membrane molecules move laterally; fluidity is influenced by temperature and lipid composition.
  • Effect of temperature on membrane fluidity
    Higher temperatures increase fluidity; lower temperatures cause phospholipids to pack tightly, reducing fluidity.
  • Role of unsaturated fatty acids in membranes
    Kinks in unsaturated fatty acid tails prevent tight packing, increasing membrane fluidity.
  • Role of cholesterol in membrane fluidity
    Acts as a fluidity buffer by preventing excessive movement at high temperatures and tight packing at low temperatures.
  • Integral membrane proteins
    Penetrate the hydrophobic interior of the bilayer; transmembrane proteins span the entire membrane.
  • Peripheral proteins
    Loosely bound to the membrane surface and do not penetrate the lipid bilayer.
  • Functions of membrane proteins
    Include transport, enzymatic activity, signal transduction, cell recognition, intercellular joining, and attachment to cytoskeleton.
  • Membrane carbohydrates
    Covalently bonded to lipids or proteins; important for cell-cell recognition and differentiation.
  • Selective permeability
    Membrane allows some substances to cross while blocking others; hydrophobic molecules cross easily, hydrophilic do not.
  • Transport proteins
    Help specific ions and molecules cross the membrane; include channel proteins and carrier proteins.
  • Passive transport
    Diffusion of substances across membranes without energy input, moving down their concentration gradient.
  • Osmosis
    Passive transport of water across a selectively permeable membrane from low to high solute concentration.
  • Tonicity
    Ability of a solution to cause a cell to gain or lose water based on solute concentration relative to the cell.
  • Isotonic, hypertonic, hypotonic solutions
    Isotonic: no net water movement; hypertonic: cell loses water; hypotonic: cell gains water and may burst.
  • Osmoregulation
    Control of water balance in organisms to prevent damage from hypotonic or hypertonic environments.
  • Facilitated diffusion
    Passive transport of molecules down their concentration gradient via specific transport proteins.
  • Gated channels
    Ion channels that open or close in response to stimuli such as electrical, chemical, or physical signals.
  • Active transport
    Energy-requiring process that moves substances against their concentration gradient using ATP.
  • Sodium-potassium pump
    Active transport pump that moves 3 sodium ions out and 2 potassium ions into the cell, maintaining gradients.
  • Membrane potential
    Voltage difference across a membrane, with the inside of the cell negative relative to the outside.
  • Electrochemical gradient
    Combination of an ion's concentration gradient and membrane potential driving ion diffusion.
  • Electrogenic pumps
    Pumps that generate voltage gradients across membranes, e.g., sodium-potassium pump and proton pumps.
  • Cotransport
    Coupled transport where the movement of one solute down its gradient powers the active transport of another solute.
  • Endocytosis
    Process by which cells engulf substances by forming vesicles from the plasma membrane.
  • Exocytosis
    Process where vesicles fuse with the plasma membrane to release contents outside the cell.
  • Phagocytosis vs. pinocytosis
    Phagocytosis is cellular eating of particles; pinocytosis is cellular drinking of fluids.
  • Receptor-mediated endocytosis
    Selective uptake of specific molecules via receptors that bind ligands triggering vesicle formation.