Membrane-structure-and-function
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Questions and Answers

What effect does cholesterol have on the fluidity of the membrane?

  • Decreases fluidity by intercalating among phospholipids (correct)
  • Has no effect on membrane fluidity
  • Only affects the membrane at high temperatures
  • Increases fluidity by making the membrane thicker

    • How do charged molecules typically cross membranes?

  • Using ligand- or voltage-gated ion channels (correct)
  • By active transport regardless of the concentration gradient
  • Through simple diffusion without any transport proteins
  • By facilitated diffusion using carrier proteins only

    • What classification does not apply to major ATP-driven pumps?

  • D (dilution) pumps (correct)
  • F (energy factors) pumps
  • ABC transporters
  • P (phosphorylated) pumps

    • Which mechanism is used for transporting large molecules across the membrane?

    <p>Exocytosis or endocytosis (B)</p> Signup and view all the answers

    What can mutations in membrane proteins potentially lead to?

    <p>Disruption of cellular signal pathways or diseases (A)</p> Signup and view all the answers

    What is the primary function of the cell membrane?

    <p>Contains and protects the cell while regulating molecular traffic (D)</p> Signup and view all the answers

    Which components primarily make up the structure of the cell membrane?

    <p>Lipid bilayer, proteins, and carbohydrates (C)</p> Signup and view all the answers

    What is the role of integral proteins in the cell membrane?

    <p>To allow for selective and bi-directional transport (A)</p> Signup and view all the answers

    What characterizes the organization of a lipid bilayer in the cell membrane?

    <p>Hydrophilic heads directed outward and hydrophobic tails oriented toward each other (D)</p> Signup and view all the answers

    Which of the following processes does NOT contribute to the semi-permeability of the cell membrane?

    <p>Mitosis (A)</p> Signup and view all the answers

    What defines the main characteristic of peripheral proteins in the cell membrane?

    <p>They are attached to the outer or inner membrane surface (A)</p> Signup and view all the answers

    Which statement about the lipid bilayer is correct?

    <p>It consists of two sheets of phospholipids with hydrophilic heads facing outward (B)</p> Signup and view all the answers

    What is the significance of gap junctions in the cell membrane?

    <p>They facilitate communication between adjacent cells (D)</p> Signup and view all the answers

    Flashcards

    Cell Membrane Function

    The cell membrane acts as a barrier, protecting the cell's contents and controlling what goes in and out.

    Selective Permeability

    The cell membrane is selectively permeable, meaning it allows certain substances to pass through while blocking others.

    Lipid Bilayer

    The cell membrane's structure is a two-layered sheet of phospholipids, with the hydrophilic heads facing outward and the hydrophobic tails facing inward.

    Membrane Proteins

    Proteins embedded within the cell membrane play a crucial role in transporting substances across the membrane.

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    Integral vs. Peripheral Proteins

    Integral membrane proteins are permanently embedded in the lipid bilayer, while peripheral proteins are only temporarily attached.

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    Selective Transport

    Membrane proteins ensure that the transport of molecules across the membrane is specific and controlled.

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    Bi-directional Transport

    Transport across the membrane can move substances in both directions, allowing for communication and exchange between the cell and its environment.

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    Gap Junctions

    Gap junctions are specialized channels that allow direct communication between adjacent cells, facilitating rapid exchange of ions and small molecules.

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    Membrane Fluidity

    The tail of a phospholipid is in "trans" configuration, which makes the membrane more fluid. However, cholesterol intercalates among the phospholipids, reducing fluidity.

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    Simple Diffusion

    Certain hydrophobic molecules can move across membranes from an area of high concentration to low concentration without needing help.

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    Facilitated Diffusion

    Glucose enters cells using specific carrier proteins called transporters, moving down a concentration gradient.

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    ATP-driven pumps

    These pumps use ATP for energy to move ions across membranes, playing a vital role in maintaining cell function.

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    Ligand- or Voltage-gated Ion Channels

    Charged molecules such as Na+, K+, and Ca2+ move across membranes down their electrochemical gradient through channels that open in response to specific signals.

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    Study Notes

    Membrane Structure and Function

    • Cell membranes enclose and protect cells, regulating substances entering and leaving.
    • Membranes are semi-permeable, maintaining internal and external composition differences. Mechanisms like transporters, channels, and endocytosis/exocytosis control this.
    • Membranes are primarily a lipid bilayer, constructed from phospholipids.
    • Phospholipid heads are hydrophilic and face the aqueous environment, while the tails are hydrophobic and face inwards.
    • Cholesterol is embedded within the bilayer and influences membrane fluidity.
    • Membrane proteins are either integral (firmly embedded) or peripheral (loosely attached). These proteins facilitate transport, signaling, and other functions.

    Membrane Fluidity

    • Unsaturated hydrocarbon tails have kinks, which increases fluidity. Saturated tails are straight, which decreases fluidity.
    • Cholesterol intercalates amongst phospholipids to regulate fluidity

    Membrane Proteins

    • Membrane proteins often act as channels or transporters for specific molecules
    • Involved in signal transduction
    • Crucial for bi-directional transport

    Types of Transport

    • Simple diffusion: molecules move from high to low concentration without protein assistance
    • Facilitated diffusion: molecules move down their concentration gradient, often through protein channels
    • Active transport: molecules move against their concentration gradient, requiring energy (ATP).

    Types of Endocytosis

    • Phagocytosis ("cell eating"): cell engulfs large particles or cells via pseudopods
    • Pinocytosis ("cell drinking"): cell takes in small droplets of extracellular fluid
    • Receptor-mediated endocytosis: specific receptors bind to target molecules, bringing them into the cell in vesicles

    Membrane Disorders

    • Mutations affecting membrane proteins can cause various diseases, impacting transport and other critical functions.
    • Examples include achondroplasia, familial hypercholesterolemia, cystic fibrosis, long QT syndrome, Wilson disease, and I-cell disease. These are caused by various mutations of genes involved in cell membrane structures/function. Genetic defects can lead to various diseases.

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