Cell Membrane Structure and Fluidity
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Cell Membrane Structure and Fluidity

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Questions and Answers

What effect do shorter tails have on transmembrane proteins?

  • They decrease the fluidity of the membrane.
  • They increase the stability of the membrane.
  • They allow for easier movement of transmembrane proteins. (correct)
  • They enhance protein binding to the cytoskeleton.

    • How does the presence of double bonds affect lipid behavior in the membrane?

  • They create a kink in the lipid tail, enhancing membrane fluidity. (correct)
  • They make lipids more rigid.
  • They decrease the overall number of lipids.
  • They prevent lipids from forming bilayers.

    • What is the role of cholesterol in cell membranes?

  • It acts solely as a barrier against toxins.
  • It promotes the movement of lipids only.
  • It stabilizes membranes, affecting fluidity based on temperature. (correct)
  • It enhances the fluidity of membranes at all temperatures.

    • What percentage of membrane proteins may be restricted in their movement?

    <p>Between 10% and 70%</p> Signup and view all the answers

    Where does the synthesis of lipids primarily occur in eukaryotic cells?

    <p>In the cytosol and smooth endoplasmic reticulum.</p> Signup and view all the answers

    What is the first destination for most transmembrane proteins after synthesis?

    <p>Endoplasmic reticulum membrane.</p> Signup and view all the answers

    What is glycosylation?

    <p>The attachment of carbohydrates to proteins or lipids.</p> Signup and view all the answers

    What is N-linked glycosylation?

    <p>Attaching carbohydrates to the nitrogen atom of asparagine.</p> Signup and view all the answers

    Which molecules can pass through a phospholipid bilayer most easily?

    <p>Gases and small uncharged molecules.</p> Signup and view all the answers

    What happens when cells face temperature changes?

    <p>They may alter their lipid composition.</p> Signup and view all the answers

    What define the selectivity of the plasma membrane?

    <p>The hydrophobic interior and membrane proteins.</p> Signup and view all the answers

    What defines the process of active transport?

    <p>It requires energy to transport substances against their concentration gradient.</p> Signup and view all the answers

    What typically characterizes the permeability of ions across the membrane?

    <p>Very low permeability.</p> Signup and view all the answers

    How does HbA1c test benefit diabetes management?

    <p>It measures the average blood sugar control over three months.</p> Signup and view all the answers

    What is the primary structure that makes up the framework of biological membranes?

    <p>Phospholipid bilayer</p> Signup and view all the answers

    Which type of membrane protein is physically embedded in the phospholipid bilayer?

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

    What characteristic of phospholipids contributes to their arrangement in biological membranes?

    <p>Amphipathic nature</p> Signup and view all the answers

    What is required for the 'flip-flop' movement of lipids between the leaflets of a membrane?

    <p>Flippase activity</p> Signup and view all the answers

    What distinguishes lipid rafts from the rest of the membrane?

    <p>High concentration of cholesterol</p> Signup and view all the answers

    Which factor does NOT affect the fluidity of membranes?

    <p>Presence of enzymes</p> Signup and view all the answers

    Which type of protein is attached to the membrane via a covalent bond to a lipid molecule?

    <p>Lipid-anchored proteins</p> Signup and view all the answers

    How do lipids primarily move within the membrane?

    <p>Lateral movement</p> Signup and view all the answers

    What best describes the Fluid-Mosaic Model of membranes?

    <p>Dynamic structure with elements able to move relative to one another</p> Signup and view all the answers

    Which property of membrane lipids contributes to their behavior as a fluid structure?

    <p>Shorter acyl tails lead to reduced interaction</p> Signup and view all the answers

    What happens to animal cells in a hypertonic solution?

    <p>They shrink and undergo crenation</p> Signup and view all the answers

    What process prevents osmotic lysis in plant cells when taking up water?

    <p>Cell wall</p> Signup and view all the answers

    Which type of transport protein uses energy to move solutes against their concentration gradient?

    <p>Active transporters</p> Signup and view all the answers

    What is the primary role of Na+/K+ -ATPase in cells?

    <p>Generates electrochemical gradients</p> Signup and view all the answers

    What characterizes receptor-mediated endocytosis?

    <p>It is driven by specific receptors in the plasma membrane</p> Signup and view all the answers

    Which of the following best describes osmosis?

    <p>Water moves to balance solute concentrations across a membrane</p> Signup and view all the answers

    What is plasmolysis in plant cells?

    <p>Plasma membrane detachment from the cell wall</p> Signup and view all the answers

    How do contractile vacuoles help freshwater protists like Paramecium?

    <p>Maintain constant cell volume by expelling water</p> Signup and view all the answers

    What is a characteristic of gated channels in cell membranes?

    <p>Transition from open to closed states controlled by ligands</p> Signup and view all the answers

    Which of the following describes secondary active transport?

    <p>It relies on gradients created by primary active transport</p> Signup and view all the answers

    What is the function of transport proteins in membranes?

    <p>Facilitate movement of ions and hydrophilic molecules</p> Signup and view all the answers

    What is the definition of osmosis?

    <p>The movement of water across a selectively permeable membrane</p> Signup and view all the answers

    What does active transport require that passive transport does not?

    <p>Cellular energy input</p> Signup and view all the answers

    Study Notes

    Membrane Structure

    • The cell membrane is a phospholipid bilayer
    • The phospholipid bilayer consists of two layers of phospholipids
    • Phospholipids are amphipathic, with hydrophilic heads and hydrophobic tails
    • The hydrophilic heads face the aqueous environment, while the hydrophobic tails face each other inside the membrane
    • Cell membranes also contain proteins and carbohydrates
    • The two layers of the phospholipid bilayer are asymmetrical: they contain different amounts of lipids, proteins, and carbohydrates

    Fluidity of Membranes

    • The cell membrane is a fluid structure meaning that phospholipids and proteins can move laterally within the membrane
    • Membrane fluidity is influenced by fatty acid tail length, degree of saturation, and cholesterol content
    • Shorter fatty acid tails and unsaturation increase membrane fluidity
    • Cholesterol can stabilize membranes at high temperatures and decrease fluidity at low temperatures

    Synthesis of Membrane Components

    • Lipids are synthesized in the smooth endoplasmic reticulum (ER)
    • Fatty acid building blocks are made by enzymes in the cytosol
    • Membrane proteins are synthesized on ribosomes and inserted into the ER membrane
    • Most proteins destined for the plasma membrane first go to the ER
    • Glycosylation occurs in the ER and Golgi apparatus

    Overview of Membrane Transport

    • Biological membranes are selectively permeable, allowing some molecules to pass through while blocking others
    • Membrane transport can be passive or active
    • Passive transport does not require energy: simple diffusion and facilitated diffusion
    • Active transport requires energy to move molecules against their concentration or electrochemical gradient

    Proteins That Carry Out Membrane Transport

    • Transport proteins are transmembrane proteins that provide a pathway for the movement of ions and molecules across membranes
    • Channels form open passageways for facilitated diffusion
    • Transporters bind to a solute and undergo a conformational change to move them across the membrane
    • Transporters can be uniporters, symporters, or antiporters

    Exocytosis and Endocytosis

    • Exocytosis and endocytosis are processes used to transport large molecules and polysaccharides
    • Exocytosis involves the packaging of material inside the cell into vesicles and their release into the extracellular medium
    • Endocytosis involves the invagination of the plasma membrane to form vesicles that bring substances into the cell
    • There are three types of endocytosis: receptor-mediated endocytosis, pinocytosis, and phagocytosis

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    Chapter 5 Membrane Structure, Synthesis, and Transport PDF

    Description

    Explore the intricate structure and dynamics of the cell membrane. This quiz covers phospholipid bilayers, membrane fluidity, and the impact of various components on membrane stability. Test your knowledge about the synthesis of membrane components and their functions.

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