Cell Membrane Structure & Function
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Questions and Answers

How does temperature affect membrane fluidity?

  • Fluidity increases as temperatures decrease.
  • Fluidity decreases as temperatures decrease.
  • Fluidity remains constant regardless of temperature.
  • Fluidity increases as temperatures increase. (correct)

    • What structural feature of unsaturated fatty acids contributes to the increased fluidity of membranes?

  • They are fully hydrogenated.
  • They have a higher surface area for van der Waals interactions.
  • Their kinks prevent tight packing. (correct)
  • Their long carbon chains allow tight packing.

    • Which statement about cholesterol in membranes is true?

  • Cholesterol only decreases membrane fluidity at cool temperatures.
  • Cholesterol acts as a fluidity buffer, affecting fluidity based on temperature. (correct)
  • Cholesterol increases fluidity in both warm and cool temperatures.
  • Cholesterol solely functions to increase membrane rigidity.

    • What region of an integral protein typically consists of non-polar amino acids?

    <p>The hydrophobic regions</p> Signup and view all the answers

    What characteristic of phospholipids allows them to form bilayers in the plasma membrane?

    <p>They are amphipathic molecules.</p> Signup and view all the answers

    Why are membranes rich in shorter fatty acid chains more fluid than those rich in longer chains?

    <p>They have less surface area for stabilizing interactions.</p> Signup and view all the answers

    What is the primary function of membrane proteins?

    <p>To determine the membrane’s specific functions.</p> Signup and view all the answers

    Which interaction is primarily responsible for the fluidity of cell membranes?

    <p>Hydrophobic interactions among fatty acid chains.</p> Signup and view all the answers

    What is the primary function of the contractile vacuole in Paramecium?

    <p>To pump water out of the cell</p> Signup and view all the answers

    What occurs to a plant cell when it is placed in a hypotonic solution?

    <p>The cell walls prevent it from bursting.</p> Signup and view all the answers

    What distinguishes facilitated diffusion from active transport?

    <p>Facilitated diffusion does not require energy.</p> Signup and view all the answers

    In a hypertonic environment, what is the potential outcome for plant cells?

    <p>The cells will undergo plasmolysis.</p> Signup and view all the answers

    What type of transport protein allows specific molecules to cross the membrane without energy?

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

    During active transport, what is the role of ATP?

    <p>It provides energy to move solutes against their gradients.</p> Signup and view all the answers

    What happens to a plant cell in isotonic conditions?

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

    Which protein undergoes a shape change to transport solutes across the membrane?

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

    What mechanism is primarily used by cells to maintain water balance in a hypertonic environment?

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

    Which of the following correctly defines the process of plasmolysis?

    <p>The detachment of the cell membrane from the cell wall in hypertonic conditions.</p> Signup and view all the answers

    What is the primary distinction between facilitated diffusion and active transport?

    <p>Active transport requires energy and membrane-bound transport proteins</p> Signup and view all the answers

    Which type of transport is primarily responsible for taking in macromolecules through vesicle formation?

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

    What term describes the simultaneous transport of two molecules in the same direction across a membrane?

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

    Which of the following correctly describes phagocytosis?

    <p>Engulfs solid particles in a vacuole</p> Signup and view all the answers

    Which molecules are typically involved in facilitated diffusion?

    <p>Ions and polar molecules</p> Signup and view all the answers

    What is the main mechanism through which exocytosis operates?

    <p>Fusion of transport vesicles with the cell membrane</p> Signup and view all the answers

    Which of these statements is true regarding receptor-mediated endocytosis?

    <p>It relies on ligand binding to trigger vesicle formation</p> Signup and view all the answers

    What type of transport requires membrane-bound proteins but does not require energy?

    <p>Facilitated diffusion</p> Signup and view all the answers

    In what process do cells take in fluids from the extracellular environment?

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

    Which transport mechanism is characterized by moving two molecules in opposite directions?

    <p>Co-transport in antiport</p> Signup and view all the answers

    What is the primary role of membrane carbohydrates in cell-cell recognition?

    <p>To bind to and identify other cells</p> Signup and view all the answers

    Which of the following is characteristic of passive transport across a membrane?

    <p>It results in no work being done to move substances</p> Signup and view all the answers

    What is the effect of a hypertonic solution on an animal cell?

    <p>The cell loses water and shrivels</p> Signup and view all the answers

    What distinguishes channel proteins from carrier proteins?

    <p>Carrier proteins bind to molecules and facilitate their movement</p> Signup and view all the answers

    Which type of molecule is most likely to pass through the plasma membrane without assistance?

    <p>Hydrophobic (non-polar) molecules</p> Signup and view all the answers

    In which scenario would osmosis cause water to move out of a cell?

    <p>When the cell is placed in a hypertonic solution</p> Signup and view all the answers

    Which of the following accurately describes the process of diffusion?

    <p>It is the movement of molecules along their concentration gradient.</p> Signup and view all the answers

    What is the term used to describe a solution with a solute concentration equal to that inside a cell?

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

    What happens to water when it moves through aquaporins?

    <p>Water passes through the membrane via a specific channel</p> Signup and view all the answers

    Which process allows the cell to recognize and interact with other cells?

    <p>Cell-cell recognition through surface molecules</p> Signup and view all the answers

    Study Notes

    Cell Membrane Structure & Function

    • Phospholipids are the most abundant lipids in the plasma membrane.
    • Phospholipids are amphipathic molecules, meaning they have both hydrophobic and hydrophilic regions.
    • The fluid mosaic model describes the plasma membrane as a fluid structure with various proteins embedded in it.

    Fluidity of Membranes

    • Phospholipids in the plasma membrane can move within the bilayer.
    • Most lipids and some proteins drift laterally or rotate within the membrane.
    • Flip-flop of molecules across the membrane is rare.

    Temperature and Membrane Fluidity

    • As temperature increases, membranes transition from a solid (gel) state to a more fluid state.
    • Membranes with shorter fatty acid chains are more fluid than those with longer chains. Shorter chains result in less surface area and fewer van der Waals/hydrophobic interactions between neighboring phospholipid molecules.
    • Membranes rich in unsaturated fatty acids are more fluid than those rich in saturated fatty acids. Unsaturated fatty acid kinks prevent tight packing.

    Cholesterol and Membrane Fluidity

    • In animal cells, cholesterol affects membrane fluidity differently at different temperatures.
    • At warm temperatures, cholesterol restrains phospholipid movement, decreasing membrane fluidity.
    • At cool temperatures, cholesterol prevents tight packing and increases membrane fluidity.

    Membrane Proteins and Their Functions

    • A membrane is a collection of different proteins embedded in the fluid matrix of the lipid bilayer.
    • Proteins determine most of the membrane's specific functions.
    • Peripheral proteins are bound to the membrane surface.
    • Integral proteins penetrate the hydrophobic core.
    • Transmembrane proteins span the membrane.
    • The hydrophobic regions of integral proteins consist of nonpolar amino acids, often coiled into α-helices.

    Six Major Functions of Membrane Proteins

    • Transport
    • Enzymatic activity
    • Signal transduction
    • Cell-cell recognition
    • Intercellular joining
    • Attachment to the cytoskeleton and extracellular matrix (ECM)

    Carbohydrates in Cell-Cell Recognition

    • Cells recognize each other by binding to carbohydrates on the plasma membrane.
    • Membrane carbohydrates may be bonded to lipids (glycolipids) or commonly to proteins (glycoproteins).
    • Carbohydrates vary among species, individuals, and cell types.

    Selective Permeability

    • Cells must exchange materials with their surroundings.
    • Plasma membranes are selectively permeable, regulating the cell's molecular traffic.
    • Hydrophobic molecules can dissolve in the lipid bilayer and pass through rapidly (e.g., water).
    • Polar molecules (e.g., sugars) do not cross easily.
    • Charged substances (ions) cannot pass through the lipid bilayer.

    Transport Proteins

    • Transport proteins allow passage of hydrophilic substances across the membrane.
    • Channel proteins have hydrophilic channels, acting as tunnels for molecules/ions.
    • Aquaporins facilitate the passage of water.
    • Carrier proteins bind to molecules and change shape to transport them across the membrane.

    Passive Transport

    • Diffusion is the tendency for molecules to spread out evenly in an available space.
    • Molecules diffuse down their concentration gradient, from high to low concentrations.
    • Diffusion across a biological membrane is passive transport because no energy is required.

    Osmosis

    • Osmosis is the diffusion of water across a selectively permeable membrane.
    • Water diffuses from a region of lower solute concentration to a region of higher solute concentration.

    Water Balance of Cells Without Cell Walls

    • Tonicity is a solution's ability to cause a cell to gain or lose water.
    • Isotonic solution: Solute concentration is the same as in the cell.
    • Hypertonic solution: Solute concentration is higher than in the cell; cell loses water.
    • Hypotonic solution: Solute concentration is lower than in the cell; cell gains water (and may burst).

    Water Balance of Cells with Cell Walls

    • Cell walls help maintain water balance.
    • A plant cell in a hypotonic solution will swell until the wall prevents further uptake, becoming turgid.
    • In an isotonic solution, there is no net water movement, and the cell becomes flaccid.
    • In a hypertonic solution, the plasma membrane pulls away from the cell wall, a process called plasmolysis.

    Facilitated Diffusion

    • In facilitated diffusion, transport proteins speed passive movement of molecules across the membrane.
    • Channel proteins provide corridors for specific molecules/ions.
    • Aquaporins facilitate water diffusion.
    • Ion channels open/close in response to stimuli (gated channels).
    • Carrier proteins change shape to translocate solute-binding sites across the membrane.

    Active Transport

    • Active transport moves substances against their concentration gradient (low to high).
    • Active transport requires energy, usually in the form of ATP.
    • The sodium-potassium pump is an example of active transport.

    Bulk Transport

    • Exocytosis is the process where transport vesicles fuse with the membrane to release their contents.
    • Endocytosis is the process where the cell takes in macromolecules by forming new vesicles from the plasma membrane.
    • Phagocytosis ("cellular eating"): Engulfing a solid particle.
    • Pinocytosis ("cellular drinking"): Taking up fluid.
    • Receptor-mediated endocytosis: Binding of ligands to receptors triggers vesicle formation.

    Co-transport

    • Symport: Two molecules transported in the same direction.
    • Antiport: Two molecules transported in opposite directions.

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    BISC 101 Cell Membrane Structure & Function STUDENT COPY PDF

    Description

    Explore the essential components and characteristics of cell membranes, including the structure and function of phospholipids. This quiz also covers the fluidity of membranes and how temperature affects their behavior. Test your knowledge on the fluid mosaic model and the effects of fatty acids.

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