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Membrane Structure and Function

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Terms in this set (25)

  • What is the fluid mosaic model of cellular membranes?
    Cellular membranes are fluid mosaics of lipids and proteins, mainly phospholipids arranged in a bilayer with embedded proteins.
  • What are phospholipids and their key property in membranes?
    Phospholipids are amphipathic molecules with hydrophilic heads and hydrophobic tails, forming the plasma membrane bilayer.
  • What does freeze-fracture technique reveal about membranes?
    Freeze-fracture splits membranes along the phospholipid bilayer, supporting the fluid mosaic model by showing protein distribution.
  • How do phospholipids move within the membrane?
    Phospholipids exhibit lateral movement (~10^7 times per second) and rare flip-flop movement across the bilayer.
  • How does temperature affect membrane fluidity?
    Membranes switch from fluid to solid state as temperature cools; fluidity depends on lipid types like saturated or unsaturated tails.
  • What role does cholesterol play in membrane fluidity?
    Cholesterol modulates fluidity by preventing tight packing at low temperatures and restraining movement at high temperatures.
  • List six major functions of membrane proteins.
    Transport, enzymatic activity, signal transduction, cell-cell recognition, intercellular joining, and attachment to cytoskeleton/ECM.
  • How do membrane carbohydrates contribute to cell recognition?
    Carbohydrates covalently bonded to lipids (glycolipids) or proteins (glycoproteins) enable cells to recognize each other.
  • What is selective permeability of membranes?
    Membranes regulate molecular traffic, allowing hydrophobic molecules to pass easily but restricting polar molecules.
  • What are transport proteins and their types?
    Transport proteins facilitate hydrophilic molecule passage; types include channel proteins (e.g., aquaporins) and carrier proteins.
  • Define passive transport and diffusion.
    Passive transport is diffusion across membranes without energy; diffusion is molecules spreading evenly in available space.
  • What is osmosis?
    Osmosis is the diffusion of water across a selectively permeable membrane from low to high solute concentration.
  • Explain tonicity and its effects on cells.
    Tonicity describes solution's effect on cell water balance: isotonic (no change), hypertonic (cell loses water), hypotonic (cell gains water).
  • What is facilitated diffusion?
    Facilitated diffusion uses transport proteins to speed passive movement of molecules across membranes without energy.
  • What is active transport?
    Active transport moves substances against concentration gradients using energy, usually ATP, via specific membrane proteins.
  • Describe the sodium-potassium pump.
    An active transport system exchanging 3 Na+ out and 2 K+ into the cell, maintaining concentration gradients and membrane potential.
  • What is membrane potential?
    Membrane potential is the voltage difference across a membrane caused by ion distribution differences.
  • What forces drive ion diffusion across membranes?
    The electrochemical gradient combines chemical concentration gradient and electrical membrane potential forces.
  • What is an electrogenic pump?
    A transport protein that generates voltage across a membrane, e.g., sodium-potassium pump in animals or proton pump in plants.
  • What is cotransport?
    Cotransport is coupled transport where a membrane protein moves two substances simultaneously, often using a gradient.
  • What are exocytosis and endocytosis?
    Bulk transport processes where cells export materials via vesicles (exocytosis) or import via vesicle formation (endocytosis).
  • Name three types of endocytosis.
    Phagocytosis (cell eating), pinocytosis (cell drinking), and receptor-mediated endocytosis (ligand-specific uptake).
  • How does phagocytosis work?
    A cell engulfs particles into a vacuole that fuses with lysosomes for digestion.
  • What happens during pinocytosis?
    Extracellular fluid is 'gulped' into tiny vesicles for nonspecific uptake of molecules.
  • Explain receptor-mediated endocytosis.
    Specific ligands bind receptors triggering vesicle formation to selectively import molecules.