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General Biology: Cell Structure, Membranes, and Cell Communication

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  • What are phospholipids and why are they important in cell membranes?
    Phospholipids are amphipathic molecules with hydrophilic heads and hydrophobic tails that form the lipid bilayer, creating a selective barrier in cell membranes.
  • Define amphipathic in the context of membrane lipids.
    An amphipathic molecule has both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions, essential for forming membrane bilayers.
  • What role does cholesterol play in the plasma membrane?
    Cholesterol modulates membrane fluidity and stability by preventing tight packing of phospholipids.
  • What is the fluid mosaic model?
    The fluid mosaic model describes the plasma membrane as a dynamic structure with proteins embedded in or attached to a fluid lipid bilayer.
  • Name three factors that determine plasma membrane fluidity.
    Membrane fluidity is influenced by temperature, cholesterol content, and the types of phospholipid fatty acids (saturated vs. unsaturated).
  • What are the three categories of transmembrane proteins and their functions?
    Transport proteins move molecules, receptor proteins receive signals, and enzymatic proteins catalyze reactions at the membrane.
  • Which molecules can cross the plasma membrane easily?
    Small nonpolar molecules like O2 and CO2 cross easily; large or charged molecules require assistance.
  • Explain passive transport across the plasma membrane.
    Passive transport moves molecules down their concentration gradient without energy, including simple diffusion, osmosis, and facilitated diffusion.
  • Why does active transport require ATP?
    Active transport moves molecules against their concentration gradient, requiring ATP to power transport proteins.
  • What is the function of the Sodium-Potassium Pump?
    The Sodium-Potassium Pump uses ATP to exchange 3 Na+ ions out and 2 K+ ions into the cell, maintaining membrane potential.
  • Differentiate prokaryotes and eukaryotes.
    Prokaryotes lack a nucleus and membrane-bound organelles; eukaryotes have a nucleus and complex organelles.
  • What is the endomembrane system?
    The endomembrane system includes organelles like the nuclear envelope, ER, Golgi apparatus, lysosomes, and vesicles involved in protein and lipid processing.
  • Name the main functions of mitochondria and chloroplasts.
    Mitochondria generate ATP via cellular respiration; chloroplasts conduct photosynthesis in plant cells.
  • What are the three types of cytoskeletal fibers and their roles?
    Microfilaments support cell shape and movement, intermediate filaments provide mechanical strength, and microtubules assist in vesicle transport and cell division.
  • How do motor proteins interact with the cytoskeleton?
    Motor proteins like kinesin move along microtubules or actin filaments to transport vesicles and enable cell movement.
  • What is actin-myosin and its role?
    Actin-myosin interaction drives muscle contraction and cellular movements by sliding filaments past each other.
  • What are the three stages of cell signaling?
    Cell signaling involves reception of a signal, transduction of the signal inside the cell, and response to the signal.
  • Name five types of cell-to-cell communication.
    Cells communicate via endocrine, paracrine, autocrine, juxtacrine (direct contact), and synaptic signaling.
  • What are plasmodesmata and gap junctions?
    Plasmodesmata are channels between plant cells; gap junctions connect animal cells, allowing direct cytoplasmic exchange.
  • Why is signal transduction and amplification important?
    Signal transduction converts external signals into cellular responses, and amplification ensures a small signal triggers a large response.