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Lipids, Membranes, and the First Cells - General Biology

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Termini in questo insieme (21)

  • What is the primary function of the plasma membrane?
    Separates life from nonlife, acts as a selective barrier allowing entry of needed materials, keeping damaging materials out, and facilitating necessary chemical reactions.
  • What defines lipids chemically?
    Carbon-containing compounds insoluble in water due to a high proportion of nonpolar bonds.
  • What are hydrocarbons and their property?
    Nonpolar molecules containing only carbon and hydrogen, making them hydrophobic.
  • What is an isoprenoid and its biological roles?
    A hydrocarbon chain that functions as pigments, scents, vitamins, sex hormone precursors, and building blocks for complex lipids.
  • What is a fatty acid?
    A hydrocarbon chain bonded to a polar carboxyl (–COOH) functional group, typically containing 14–20 carbon atoms.
  • Difference between saturated and unsaturated fatty acids?
    Saturated fatty acids have only single bonds and maximum hydrogens; unsaturated have one or more double bonds causing kinks in the chain.
  • How does bond saturation affect the physical state of lipids?
    Highly saturated lipids are solid at room temperature; highly unsaturated lipids are liquid at room temperature.
  • Name three important types of lipids found in cells.
    Steroids, fats (triacylglycerols), and phospholipids.
  • What structural feature defines steroids?
    A bulky, four-ring hydrocarbon structure with varying functional groups.
  • What is the primary role of fats (triacylglycerols)?
    Energy storage due to a large number of high-energy bonds in fatty acid chains.
  • How are fats formed chemically?
    By dehydration reactions linking three fatty acids to glycerol via ester linkages.
  • What distinguishes phospholipids from fats?
    Phospholipids have a glycerol linked to a phosphate group and two hydrocarbon tails, making them amphipathic.
  • What does amphipathic mean in the context of phospholipids?
    Molecules containing both hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
  • What structures do amphipathic lipids form in water?
    Micelles (spherical aggregates) and lipid bilayers (paired sheets).
  • What are liposomes?
    Artificial membrane-bound vesicles formed from phospholipids in the lab.
  • What is selective permeability of lipid bilayers?
    Ability to allow small or nonpolar molecules to cross quickly, while charged or large polar molecules cross slowly or not at all.
  • How does hydrocarbon tail length affect membrane permeability?
    Longer tails increase hydrophobic interactions, making membranes less permeable.
  • How does saturation of hydrocarbon tails affect membrane permeability?
    Unsaturated tails with kinks weaken hydrophobic packing, increasing permeability; saturated tails pack tightly, reducing permeability.
  • What effect does cholesterol have on membrane permeability?
    Cholesterol increases packing density of phospholipid tails, reducing membrane permeability.
  • How does temperature influence membrane fluidity and permeability?
    Lower temperatures decrease fluidity and permeability by slowing molecular movement and tightening tail packing.
  • What is diffusion in the context of membranes?
    Spontaneous movement of molecules from high to low concentration along a concentration gradient.