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Membrane Transport & Cell Signaling

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  • Plasma membrane structure
    The plasma membrane is a selectively permeable boundary composed mainly of amphipathic lipids and proteins, forming a fluid mosaic model.
  • Fluid mosaic model
    Describes the membrane as a mosaic of protein molecules bobbing in a fluid bilayer of phospholipids.
  • Membrane fluidity factors
    Membrane fluidity is influenced by temperature, lipid composition (unsaturated vs saturated fatty acids), and cholesterol content.
  • Effect of unsaturated vs saturated fatty acid tails
    Unsaturated tails increase fluidity due to kinks preventing tight packing; saturated tails decrease fluidity by packing tightly.
  • Role of cholesterol in membrane fluidity
    Cholesterol reduces membrane fluidity at moderate temperatures but prevents solidification at low temperatures by disrupting packing.
  • Integral vs peripheral membrane proteins
    Integral proteins penetrate the hydrophobic bilayer, often spanning it; peripheral proteins are loosely bound to membrane surfaces.
  • Six major functions of membrane proteins
    Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton/ECM.
  • Glycolipids and glycoproteins
    Carbohydrates covalently bonded to lipids or proteins on the extracellular membrane surface, important for cell recognition.
  • Selective permeability of membranes
    Hydrophobic molecules cross easily; larger polar molecules require transport proteins to cross the membrane.
  • Transport proteins types
    Channel proteins provide hydrophilic tunnels; carrier proteins bind and shuttle molecules by changing shape.
  • Passive transport
    Diffusion of substances across membranes down their concentration gradient without energy input.
  • Osmosis
    Diffusion of water across a selectively permeable membrane from lower to higher solute concentration.
  • Tonicity effects on cells without walls
    Hypotonic causes swelling/lysis; isotonic causes no net water movement; hypertonic causes shrinking.
  • Tonicity effects on plant cells
    Hypotonic solution makes cells turgid; isotonic makes cells flaccid; hypertonic causes plasmolysis.
  • Facilitated diffusion
    Passive transport aided by transport proteins moving molecules down their concentration gradient.
  • Active transport
    Energy-requiring process moving substances against their concentration gradient using ATP.
  • Sodium-potassium pump
    An active transport protein exchanging Na+ out and K+ into animal cells to maintain concentration gradients.
  • Membrane potential
    Voltage across a membrane created by differences in ion distribution, resulting in a negatively charged cell interior.
  • Electrochemical gradient
    Combined effect of membrane potential and ion concentration gradient driving ion diffusion.
  • Electrogenic pumps
    Transport proteins that generate voltage across membranes, e.g., sodium-potassium pump and proton pump.
  • Cotransport
    Coupled transport where downhill diffusion of one solute drives uphill transport of another against its gradient.
  • Bulk transport
    Energy-requiring transport of large molecules via vesicles by exocytosis (out) and endocytosis (in).
  • Types of endocytosis
    Phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis.
  • Cell signaling stages
    Reception (signal detection), transduction (signal conversion), and response (cellular activity).
  • Membrane receptors types
    G protein-coupled receptors and ligand-gated ion channels.
  • Ligand-gated ion channel receptor
    Receptor that acts as a gate for ions when a ligand binds, important in nervous system signaling.
  • Signal transduction cascade
    Multiple-step molecular interactions amplifying a signal to produce a large cellular response.
  • Cellular response to signaling
    Regulation of cytoplasmic activities or gene expression by turning genes on or off.