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General Biology: Water, Lipids, and Cell Membranes

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Termini in questo insieme (23)

  • Why is water a polar molecule?
    Oxygen has a higher electronegativity than hydrogen, pulling shared electrons closer and creating a slight negative charge on oxygen and a slight positive charge on hydrogen.
  • What are hydrogen bonds in water?
    Weak attractions between the slightly positive hydrogen of one water molecule and the slightly negative oxygen of another.
  • What property of water allows insects to walk on its surface?
    Surface tension created by cohesion of water molecules due to hydrogen bonding.
  • How do hydrogen bonds affect water's heat capacity?
    They require a lot of energy to break, allowing water to absorb large amounts of heat with little temperature change.
  • Why does ice float on liquid water?
    Hydrogen bonds in ice are stable and hold molecules farther apart, making ice less dense than liquid water.
  • What is a solvent, solute, and solution?
    Solvent: dissolving agent; Solute: substance dissolved; Solution: uniform liquid mixture of solute and solvent.
  • Why is water called the solvent of life?
    Its polarity allows it to dissolve polar and charged substances, forming aqueous solutions essential for life.
  • What ions do water molecules dissociate into in aqueous solutions?
    Hydrogen ions (H+) and hydroxide ions (OH–).
  • How is acidity measured and what does pH indicate?
    Acidity is measured on the pH scale; pH less than 7 is acidic, 7 is neutral, and greater than 7 is basic.
  • What role do buffers play in biological systems?
    Buffers resist pH changes by accepting excess H+ ions or donating H+ ions when depleted.
  • What are lipids and their general characteristics?
    Hydrophobic compounds mainly made of carbon and hydrogen, important for long-term energy storage, and contain twice as much energy as polysaccharides.
  • What are the three main types of lipids?
    Fats, phospholipids, and steroids.
  • What is the structure of a fat (triglyceride)?
    One glycerol molecule linked to three fatty acids via dehydration reactions.
  • What distinguishes saturated from unsaturated fatty acids?
    Saturated fatty acids have the maximum number of hydrogens with no double bonds; unsaturated have one or more double bonds causing kinks.
  • What are trans fats and how are they formed?
    Unsaturated fats converted to saturated fats by hydrogenation, associated with health risks.
  • How are phospholipids structurally different from fats?
    Phospholipids have two fatty acids and a phosphate group attached to glycerol, unlike fats which have three fatty acids.
  • How do phospholipids arrange themselves in cell membranes?
    They form a bilayer with hydrophilic heads facing water and hydrophobic tails facing inward.
  • What is the role of cholesterol in animal cell membranes?
    It stabilizes membranes at warm temperatures and maintains fluidity at low temperatures.
  • What is the fluid mosaic model of the cell membrane?
    A flexible membrane made of a phospholipid bilayer with embedded and attached proteins functioning together.
  • Name some functions of membrane proteins.
    Maintaining cell shape, acting as receptors, enzymes, participating in cell recognition, and forming intercellular junctions.
  • What is a glycoprotein and its function?
    A membrane protein with attached carbohydrates involved in cell-cell recognition.
  • Why is selective permeability important in membranes?
    It allows some substances to cross more easily than others, controlling the internal environment of the cell.
  • How did membranes contribute to the origin of life?
    Phospholipids spontaneously self-assemble into membranes, forming enclosed collections of molecules critical for the first cells.