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What is the primary function of the plasma membrane?

  • To facilitate chemical reactions
  • To control traffic into and out of the cell (correct)
  • To store genetic information
  • To produce energy for the cell

    • Which statement best describes the Fluid Mosaic Model?

  • The membrane consists of a uniform layer of phospholipids only.
  • The membrane is static and does not allow for movement.
  • The membrane is a mosaic of proteins embedded in a fluid bilayer. (correct)
  • The membrane is a rigid structure with fixed proteins.

    • What are phospholipids primarily known for in the plasma membrane?

  • Serving as receptors for signaling molecules
  • Being the most abundant lipid in the membrane (correct)
  • Facilitating active transport across the membrane
  • Providing structural stability

    • Which of the following mechanisms does NOT contribute to selective permeability of the plasma membrane?

    <p>High temperatures stabilizing the membrane</p> Signup and view all the answers

    What is a characteristic feature of membrane proteins?

    <p>They serve specific functions such as transport and signaling.</p> Signup and view all the answers

    How do hydrophobic interactions contribute to plasma membrane structure?

    <p>They hold the phospholipid bilayer together.</p> Signup and view all the answers

    Which component of the plasma membrane is responsible for selective transport of molecules?

    <p>Membrane proteins</p> Signup and view all the answers

    What effect do temperature changes have on membrane fluidity?

    <p>Increased temperature can enhance membrane fluidity.</p> Signup and view all the answers

    What role do membrane carbohydrates play in cell recognition?

    <p>They assist in cell-cell recognition.</p> Signup and view all the answers

    Which of the following best describes glycoproteins?

    <p>Proteins that have carbohydrates covalently bonded to them.</p> Signup and view all the answers

    What mechanism is involved in the rejection of foreign cells by the immune system?

    <p>Cell-cell recognition.</p> Signup and view all the answers

    Which statement is true about gap junctions?

    <p>They allow the passage of molecules directly between adjacent cells.</p> Signup and view all the answers

    What property of the cell membrane primarily limits the passage of many molecules?

    <p>The hydrophobic core of the lipid bilayer.</p> Signup and view all the answers

    How do large uncharged polar molecules generally cross the cell membrane?

    <p>They require specific transport proteins.</p> Signup and view all the answers

    What is the function of microfilaments in relation to membrane proteins?

    <p>They stabilize the location of certain membrane proteins.</p> Signup and view all the answers

    What happens to a cell placed in a hypotonic solution?

    <p>Water enters the cell and it may burst.</p> Signup and view all the answers

    Which of these is NOT a characteristic of cell-cell recognition?

    <p>It prevents the merging of similar cells.</p> Signup and view all the answers

    In which type of solution does a cell maintain its volume without net movement of water?

    <p>Isotonic solution</p> Signup and view all the answers

    What is the primary effect of placing a plant cell in a hypertonic solution?

    <p>The plasma membrane pulls away from the cell wall.</p> Signup and view all the answers

    What is the definition of tonicity?

    <p>The ability of a solution to cause a cell to gain or lose water.</p> Signup and view all the answers

    What occurs when an animal cell is placed in an isotonic environment?

    <p>There is no net movement of water.</p> Signup and view all the answers

    What primarily happens to an animal cell in a hypertonic solution?

    <p>The cell may shrivel and die.</p> Signup and view all the answers

    How does a plant cell respond to a hypotonic environment?

    <p>The cell becomes turgid and firm.</p> Signup and view all the answers

    What is the result of increasing salinity in a lake for animal cells?

    <p>Animal cells lose water to their environment.</p> Signup and view all the answers

    What is the main function of transport proteins in facilitated diffusion?

    <p>To help solutes cross membranes while following their concentration gradient</p> Signup and view all the answers

    Which type of transport protein provides specific passageways for molecules and ions?

    <p>Channel protein</p> Signup and view all the answers

    How do aquaporins function in plant and animal cells?

    <p>By facilitating rapid diffusion of water molecules across the membrane</p> Signup and view all the answers

    What distinguishes gated ion channels from non-gated ion channels?

    <p>Gated channels open or close in response to stimuli, non-gated do not</p> Signup and view all the answers

    Which stimulus can cause a gated ion channel to open or close?

    <p>Chemical ligand binding</p> Signup and view all the answers

    Which characteristic is true of non-gated or leak channels?

    <p>They are always open and facilitate ion permeability</p> Signup and view all the answers

    What process is plasmolysis associated with in plant cells?

    <p>Cell contraction and wilting</p> Signup and view all the answers

    What is the primary role of carrier proteins in facilitated diffusion?

    <p>To bind specific molecules and transport them across the membrane</p> Signup and view all the answers

    What triggers the opening of mechanically-gated ion channels?

    <p>Physical deformation</p> Signup and view all the answers

    What is the primary defect in the chloride channels of individuals with cystic fibrosis?

    <p>Defective or absent chloride transport</p> Signup and view all the answers

    What effect does the high concentration of intracellular Cl- have in cystic fibrosis?

    <p>Inhibits mucus clearance by cilia</p> Signup and view all the answers

    Which of the following accurately describes the mechanism of carrier proteins?

    <p>They bind solutes and undergo a shape change.</p> Signup and view all the answers

    What is the primary consequence of defective carrier proteins in cystinuria?

    <p>Accumulation of cystine in urine</p> Signup and view all the answers

    What common complication arises from the accumulation of thick mucus in cystic fibrosis patients?

    <p>Respiratory infections</p> Signup and view all the answers

    How does extracellular Cl- contribute to mucus quality in cystic fibrosis?

    <p>It attracts water to maintain mucus consistency.</p> Signup and view all the answers

    What is a common symptom of cystinuria due to the accumulation of cystine?

    <p>Formation of kidney stones</p> Signup and view all the answers

    What is the main purpose of active transport in cells?

    <p>To enable cells to maintain specific internal concentrations of solutes.</p> Signup and view all the answers

    Which of the following accurately describes the sodium-potassium pump?

    <p>It exchanges Na+ for K+ against their concentration gradients.</p> Signup and view all the answers

    What is generated across a membrane by an electrogenic pump?

    <p>An electrochemical gradient.</p> Signup and view all the answers

    Which component is crucial for the functioning of cotransport systems?

    <p>The movement of one solute down its concentration gradient.</p> Signup and view all the answers

    What role does ATP play in active transport?

    <p>It directly powers the transport of solutes across the membrane.</p> Signup and view all the answers

    What happens when the proton pump operates in plant cells?

    <p>H+ ions accumulate outside the cell.</p> Signup and view all the answers

    What is a key benefit of having a high concentration of ions outside the cell in the context of cotransport?

    <p>It drives the uptake of nutrients against their gradients.</p> Signup and view all the answers

    Which of the following is an example of an electrogenic pump?

    <p>The sodium-potassium pump.</p> Signup and view all the answers

    Study Notes

    Plasma Membrane Transport

    • Chapter 3 of BIO091, Semester 1, 2024/2025
    • Learning outcomes:
      • List components of plasma membrane and their function
      • Describe plasma membrane structure and the functions of components
      • Explain the role of membrane proteins
      • Explain how membrane structure results in selective permeability
      • Explain various transport mechanisms across the membrane

    Membrane Components and Organization

    • The plasma membrane separates the living cell from its surroundings.
    • It controls traffic into and out of the cell
    • It exhibits selective permeability.
    • Phospholipids: The most abundant lipid in the plasma membrane, amphipathic (hydrophobic and hydrophilic regions).

    Structure of Plasma Membrane - Fluid Mosaic Model

    • Proposed by Singer and Nicolson in 1972.
    • The membrane is a mosaic of proteins embedded in a fluid bilayer of phospholipids.

    Membrane Proteins and Their Functions

    • Peripheral proteins: Not embedded in the lipid bilayer, located on the inner or outer surface, usually bound to exposed regions of integral proteins through noncovalent interactions.
    • Integral proteins: Penetrate the hydrophobic core; amphipathic proteins.
      • Hydrophilic segments are non-helical in contact with intracellular and extracellular fluids.
      • Hydrophobic segments are a-helical secondary structures or rolled-up B-pleated sheets).
    • Six major functions of membrane proteins:
      • Transport proteins
      • Involved in enzymatic activity
      • Involved in signal transduction processes
      • Involved in cell-cell recognition
      • As intercellular joining molecules
      • Attach to the cytoskeleton and extracellular matrix (ECM)

    Membrane Structure Results in Selective Permeability

    • Small hydrophobic molecules: Can dissolve in the lipid bilayer and pass through it. (e.g., hydrocarbons, gases like CO2 and O2, and small polar but uncharged molecules like H2O and ethanol).
    • Hydrophilic molecules: Cannot easily pass through the hydrophobic core of the membrane, and often require transport proteins. (e.g., large uncharged polar molecules like glucose, small ions such as H+, Na+ and K+).
    • Transport Proteins: Allow movement of hydrophilic molecules or ions across the membrane.
      • Channel proteins: Hydrophilic channels that specific molecules or ions use as tunnels.
        • Aquaporins: Specific channel proteins that facilitate the passage of water.
        • Ion channels: Non-gated (leak): Always open and responsible for permeability of specific types of ions.
          • Gated: Open or close in response to stimulus (chemical, electrical or mechanical).
      • Carrier proteins: Bind to molecules and change shape to pass them across the membrane, specific to the substance it moves.

    Passive Transport

    • Types of passive transports:
      • Simple Diffusion
      • Osmosis
      • Facilitated Diffusion.
    • Substances move down their concentration gradient without energy input.

    Active Transport

    • Movement of ions or molecules across the membrane against their concentration gradient (needs energy).
    • Uses carrier proteins, requiring ATP.
    • Types of active transport:
      • Electrogenic pump: Transport protein that generates a voltage across a membrane (e.g sodium-potassium pump, proton pump).
      • Cotransport: Two different solutes are transported simultaneously. One solute moves down its concentration gradient, providing the energy to move the other solute against its concentration gradient (e.g. H+-sucrose cotransporter, Na+-glucose cotransporter).
      • Bulk transport:
        • Endocytosis—movement of materials into the cell by forming vesicles. Examples include Phagocytosis, Pinocytosis, and receptor-mediated endocytosis.
        • Exocytosis—movement of materials out of the cell by fusion of vesicles with the plasma membrane.
    • Cystic Fibrosis: Genetic disease causing defective or absent chloride channels, resulting in mucus buildup in various organs.
    • Cystinuria: Inherited disease causing accumulation of cystine leading to crystals and stones blocking the kidneys, ureters, or bladder.
    • Hypercholesterolemia: Disease related to defective or missing LDL receptor proteins causing cholesterol accumulation in the blood, contributing to early atherosclerosis.

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