Plasma Membrane Structure and Function
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Questions and Answers

Which of the following is NOT a function of the cell membrane?

  • Exchanging nutrients, wastes, and secretions
  • Responding to changes in the environment or signals
  • Producing energy through ATP synthesis (correct)
  • Maintaining an ionic gradient for electrical activity

    • Which of the following is a type of protein found in the cell membrane that facilitates the passage of water?

  • Carrier molecules
  • Membrane receptors
  • Docking-marker acceptors
  • Aquaporins (correct)

    • The fluid mosaic model of the cell membrane describes its structure as:

  • A rigid, fixed structure with proteins embedded in a lipid bilayer
  • A homogeneous, uniform layer of lipids and proteins without any distinct organization
  • A dynamic, fluid structure with a tri-laminar appearance (correct)
  • A static layer of proteins on the exterior of a lipid bilayer

    • Which of the following is NOT a type of specialized cell junction?

    <p>Synaptic junctions</p> Signup and view all the answers

    Which of the following extracellular matrix components is responsible for providing elasticity and flexibility to tissues?

    <p>Elastin</p> Signup and view all the answers

    Which of the following components of the cell membrane is primarily responsible for creating a barrier to the passage of water-soluble substances?

    <p>Phospholipids</p> Signup and view all the answers

    What is the primary function of glycoproteins and glycolipids in the cell membrane?

    <p>To serve as self-identity markers for cell recognition</p> Signup and view all the answers

    What is the role of cell adhesion molecules (CAMs) in cell-cell interactions?

    <p>To connect cells together through hook-like and loop-like structures, generating a velcro-like effect</p> Signup and view all the answers

    What type of junction is responsible for creating a tight seal between adjacent epithelial cells, preventing the passage of materials between cells?

    <p>Tight junctions</p> Signup and view all the answers

    Which of the following statements accurately describes the role of connexons in gap junctions?

    <p>Connexons serve as channels that allow the passage of small particles between adjacent cells.</p> Signup and view all the answers

    How does the lipid solubility of a substance affect its ability to cross a cell membrane via diffusion?

    <p>Substances with higher lipid solubility diffuse more rapidly across the membrane because they can readily dissolve in the lipid bilayer.</p> Signup and view all the answers

    Which of the following is NOT a characteristic of passive transport?

    <p>Passive transport processes involve the use of membrane proteins for transport.</p> Signup and view all the answers

    What is the driving force behind osmosis?

    <p>The difference in water concentration across a semi-permeable membrane.</p> Signup and view all the answers

    How does the electrochemical gradient influence the movement of ions across a membrane?

    <p>Ions move down the combined influence of both concentration and electrical gradients.</p> Signup and view all the answers

    When does osmosis cease in a system separated by a semi-permeable membrane?

    <p>When the water concentration is equal and the hydrostatic pressure is also equal.</p> Signup and view all the answers

    Which of the following is NOT a factor that influences the rate of diffusion?

    <p>The presence of membrane proteins that facilitate transport.</p> Signup and view all the answers

    What is the primary difference between primary and secondary active transport?

    <p>Primary active transport uses ATP directly to move substances against their concentration gradient, while secondary active transport uses the energy stored in an electrochemical gradient established by primary active transport.</p> Signup and view all the answers

    Which of the following examples represents a situation where diffusion is the primary mode of transport?

    <p>The movement of oxygen from the alveoli in the lungs into the bloodstream.</p> Signup and view all the answers

    Which of the following statements correctly describes the role of caveolae?

    <p>Caveolae are small invaginations of the plasma membrane involved in both membrane transport and signal transduction.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of desmosomes?

    <p>Desmosomes anchor cells together, providing structural integrity and resisting mechanical stress.</p> Signup and view all the answers

    What is the primary function of the plasma membrane?

    <p>Regulating the passage of substances into and out of the cell.</p> Signup and view all the answers

    Which of the following statements accurately describes the relationship between the electrical and concentration gradients in the electrochemical gradient?

    <p>The electrical and concentration gradients can either reinforce or oppose each other, influencing the net movement of ions.</p> Signup and view all the answers

    Which of the following statements accurately describes the role of the sodium-potassium pump in cellular transport?

    <p>The sodium-potassium pump uses ATP to move sodium ions out of the cell and potassium ions into the cell, against their concentration gradients.</p> Signup and view all the answers

    Study Notes

    Plasma Membrane Structure and Function

    • The plasma membrane is a lipid bilayer, a selectively permeable barrier
    • It contains phospholipids (polar head groups and nonpolar tails) and cholesterol
    • Phospholipids provide fluidity and stability to the membrane
    • Cholesterol helps maintain fluidity at different temperatures
    • Membrane proteins are embedded in the lipid bilayer, performing a variety of functions
    • Proteins can be transmembrane or peripheral (on one surface)
    • Membrane proteins include channels, carriers, receptors, enzymes, and cell-adhesion molecules

    Functions of Cell Membrane

    • Maintains homeostasis and cell survival, coordinating cell activity with other cells
    • Acts as a mechanical barrier to separate cells
    • Facilitates exchange of nutrients, wastes, and secretions from cell to cell
    • Responds to environmental changes and signals
    • Maintains ionic gradients for electrical activity

    Components of Cell Membrane: Lipids

    • Phospholipids and cholesterol form the lipid bilayer, acting as a barrier to water-soluble substances
    • It provides fluidity and stability to the membrane
    • The phospholipid's hydrophilic head group faces outward, while the hydrophobic tail group faces inward

    Components of Cell Membrane: Proteins

    • Proteins have both hydrophobic and hydrophilic regions, embedded in the lipid bilayer
    • Integral proteins are transmembrane proteins, spanning the bilayer
    • Peripheral proteins are on one surface only
    • Proteins perform diverse functions, including transport, signaling, and cell adhesion

    Components of Cell Membrane: Carbohydrates

    • Carbohydrates are present on the outer surface of the membrane only
    • Glycolipids and glycoproteins are carbohydrate chains attached to lipids or proteins
    • These form glycocalyx, functioning as self-identity markers

    Structure of Cell Membrane: Fluid Mosaic Model

    • The fluid mosaic model describes the membrane's structure as a mosaic of protein molecules embedded in a fluid bilayer of phospholipids
    • The membrane is characterized by its fluidity and the dynamic movement of components

    Cell-Cell Adhesions

    • Extracellular matrix (ECM) is a biological glue, secreted by cells to adhere cells to each other.
    • Specialized cell junctions, such as desmosomes and tight junctions, hold cells together, mediating communication and maintaining tissue integrity
    • Cell adhesion molecules (CAMs) mediate cell–cell interactions and cell–extracellular matrix interactions

    Extracellular Matrix (ECM)

    • The ECM is an area outside the cell, containing interstitial fluid and fibrous proteins
    • It acts as a filler to support and maintain the structure of cells and tissues
    • Collagen (cable-like) provides tensile strength
    • Elastin (rubber-like) allows organs to stretch
    • Fibronectin promotes cell adhesion

    Transport Across the Membrane: Overview

    • Membrane transport is crucial for maintaining homeostasis
    • The plasma membrane is selectively permeable
    • Permeability factors include lipid solubility and particle size, requiring forces to transport substances

    Transport Across the Membrane: Passive Transport

    • Passive transport does not require energy input from the cell
    • Common types include diffusion, osmosis, and facilitated diffusion
    • Diffusion is movement from high to low concentration
    • Osmosis is water movement from high to low water concentration

    Transport Across the Membrane: Active Transport

    • Active transport requires energy expenditure
    • This includes primary and secondary active transport
    • Primary active transport uses ATP directly
    • Secondary active transport uses an electrochemical gradient

    Diffusion

    • Diffusion is the net movement of a substance from high to low concentration
    • Factors influencing the diffusion rate: concentration gradient, temperature, surface area, membrane permeability, and distance

    Osmosis

    • Osmosis is the net movement of water across a semipermeable membrane from high to low water concentration
    • Tonicity describes the concentration of non-penetrating solutes
    • Osmolarity describes the total concentration of all solute particles, including penetrating and non-penetrating solutes
    • Isotonic solutions have equal solute concentrations inside and outside the cell.
    • Hypotonic solutions have a lower solute concentration than inside the cell; water moves into the cell, potentially causing the cell to burst.
    • Hypertonic solutions have a higher solute concentration than inside the cell, water moves out of the cell, potentially causing the cell to shrink.

    Carrier-Mediated Transport

    • Carrier proteins bind to specific solutes (e.g. glucose)
    • Binding changes the carrier protein's shape, moving the solute across the membrane
    • Uniport, symport, antiport are different types of carrier-mediated transport based on the direction and number of substances being moved

    Cell Junctions: Desmosomes, Tight Junctions, and Gap Junctions

    • Desmosomes/Adhering junctions are anchoring junctions that facilitate mechanical strength
    • Tight junctions create an impermeable barrier to block fluid movement between cells
    • Gap junctions allow communication between adjacent cells

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    Description

    Test your knowledge on the structure and function of the plasma membrane. This quiz covers the lipid bilayer, the roles of phospholipids and cholesterol, and the various membrane proteins. Understand how the cell membrane maintains homeostasis and facilitates cellular communication.

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