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General Biology: Cell Membranes and Perforin Cytotoxicity

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  • What role does perforin play in cytotoxic T lymphocytes (CTLs)?
    Perforin is used by CTLs to create pores in target cell membranes, allowing granzymes to enter and induce apoptosis.
  • What is the difference between perforin-1 and perforin-2?
    Perforin-1 is used by CTLs to kill virally infected or cancer cells, while perforin-2 is used by phagocytes to target phagocytosed microbes.
  • What are the main components of the eukaryotic cell boundary?
    The eukaryotic cell boundary consists of the plasma membrane and sometimes a cell wall in plants and fungi.
  • How do Gram-positive and Gram-negative bacterial cell walls differ?
    Gram-positive bacteria have a thick peptidoglycan layer with lipoteichoic acids, while Gram-negative bacteria have a thin peptidoglycan layer and an outer membrane containing lipopolysaccharides.
  • What is the structure of the archaeal cell membrane and wall?
    Archaeal membranes contain phospholipids with isoprenoid alcohols and L-glycerol ethers, and their cell walls often have an S-layer instead of peptidoglycan.
  • What is the fluid mosaic model of the plasma membrane?
    The plasma membrane is a fluid bilayer of phospholipids with embedded proteins that move laterally, creating a dynamic mosaic.
  • What does amphipathic mean in the context of glycerophospholipids?
    Amphipathic molecules have both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
  • What types of molecules can easily diffuse across the plasma membrane?
    Small, nonpolar molecules like O2, CO2, and H2O can diffuse easily across the membrane.
  • Why do large polar molecules have limited permeability across membranes?
    Large polar molecules like glucose and ions cannot easily cross the hydrophobic core of the membrane without transport proteins.
  • What is osmosis?
    Osmosis is the passive diffusion of water across a selectively permeable membrane from low to high solute concentration.
  • How does the plasma membrane regulate inbound and outbound traffic?
    Through passive transport, active transport, endocytosis, and exocytosis involving transport proteins and vesicles.
  • What is the role of transport proteins in the plasma membrane?
    Transport proteins facilitate the movement of molecules that cannot diffuse freely, either passively or actively using energy.
  • What happens to animal cells in hypotonic, isotonic, and hypertonic solutions?
    In hypotonic solutions, cells lyse; in isotonic, they remain normal; in hypertonic, they shrivel.
  • What happens to plant cells in hypotonic, isotonic, and hypertonic solutions?
    In hypotonic, cells become turgid; isotonic, flaccid; hypertonic, plasmolyzed.
  • What are the four important classes of biological molecules related to membranes?
    Lipids, proteins, carbohydrates, and nucleic acids, with lipids forming the membrane bilayer.
  • What are the key functions of lipids in cells?
    Lipids provide energy, form cell membranes, and act as hormones.
  • What is the structural formula of a phospholipid?
    A phospholipid has a hydrophilic head (choline, phosphate, glycerol) and two hydrophobic fatty acid tails.
  • What is the significance of cholesterol in the plasma membrane?
    Cholesterol modulates membrane fluidity and stability.
  • What is the raft model of the plasma membrane?
    Membrane rafts are microdomains enriched in cholesterol and sphingolipids that organize membrane proteins for signaling.
  • How do vesicles participate in membrane transport?
    Vesicles mediate bulk transport by endocytosis (inward) and exocytosis (outward) of large molecules.