Cell Membrane Structure and Composition
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Questions and Answers

Which of these is NOT a type of lipid found in the plasma membrane?

  • Glycoprotein (correct)
  • Phosphatidylcholine
  • Phosphatidylserine
  • Sphingomyelin

    • What is the primary function of membrane proteins?

  • To provide structural support for the cell
  • To regulate the movement of substances across the membrane (correct)
  • To synthesize proteins
  • To store energy

    • Which type of membrane protein is embedded within the lipid bilayer and spans the entire membrane?

  • Monolayer-associated protein
  • Integral transmembrane protein (correct)
  • Peripheral protein
  • Lipid-linked protein

    • What is the primary structural feature of a transmembrane protein that allows it to cross the lipid bilayer?

    <p>Alpha helix (C)</p> Signup and view all the answers

    How is the asymmetry of the plasma membrane maintained during membrane transfer?

    <p>The cytosolic monolayer always faces the cytosol. (D)</p> Signup and view all the answers

    What are the main mechanisms that restrict the movement of membrane proteins?

    <p>Binding to the cell cortex, extracellular matrix molecules, or proteins on other cells (D)</p> Signup and view all the answers

    Which of the following processes can be used to visualize membrane fluidity?

    <p>Fluorescence recovery after photobleaching (FRAP) (A)</p> Signup and view all the answers

    What is the main difference between integral transmembrane proteins and peripheral proteins?

    <p>Integral transmembrane proteins are permanently associated with the membrane, while peripheral proteins are not (A)</p> Signup and view all the answers

    What is the primary function of tight junctions in epithelial cells of the gut?

    <p>To prevent mixing of proteins from different sides of the plasma membrane. (D)</p> Signup and view all the answers

    How does the glycocalyx contribute to cell-cell recognition?

    <p>By presenting unique carbohydrate patterns that allow cells to identify each other. (C)</p> Signup and view all the answers

    What is the main reason for the cell membrane being considered asymmetric?

    <p>The presence of different lipid molecules on the inner and outer leaflets of the bilayer. (A)</p> Signup and view all the answers

    How is the fluidity of a cell membrane regulated?

    <p>All of the above. (D)</p> Signup and view all the answers

    Which type of membrane protein is anchored to the lipid bilayer through a covalent attachment to a lipid molecule?

    <p>Anchored protein. (B)</p> Signup and view all the answers

    How are new membrane components synthesized?

    <p>They are synthesized in the endoplasmic reticulum and then transferred to the membrane. (D)</p> Signup and view all the answers

    What is the role of the cell cortex?

    <p>It provides structural support and helps maintain cell shape. (A)</p> Signup and view all the answers

    What is the main function of the glycocalyx in tissue formation?

    <p>It helps in the adhesion of cells to each other and to the extracellular matrix. (B)</p> Signup and view all the answers

    What is the significance of the hydrophobic tails of phospholipids being shielded from water in the plasma membrane?

    <p>It allows for the formation of a stable, sealed compartment within the cell. (A)</p> Signup and view all the answers

    What type of enzyme facilitates the flipping of phospholipids between the cytosolic and non-cytosolic layers of the membrane?

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

    Which factor contributes to a more fluid plasma membrane?

    <p>Shorter fatty acid chains (D)</p> Signup and view all the answers

    Where is new membrane synthesized in the cell?

    <p>Smooth endoplasmic reticulum (B)</p> Signup and view all the answers

    What is the role of the Golgi apparatus in membrane synthesis?

    <p>Transfer specific phospholipids to the cytosolic monolayer (C)</p> Signup and view all the answers

    What is the primary function of glycolipids in the plasma membrane?

    <p>Participate in cell recognition and signaling (D)</p> Signup and view all the answers

    Which of the following statements is TRUE about the structure of the plasma membrane?

    <p>Membranes can be viewed as fluids that allow for the movement of phospholipids and proteins within the same layer. (D)</p> Signup and view all the answers

    Which of the following factors would NOT increase membrane fluidity?

    <p>Increasing the saturation degree of hydrocarbon tails (D)</p> Signup and view all the answers

    What is the primary function of the cell cortex in red blood cells?

    <p>To provide structural support and maintain the cell's biconcave shape. (C)</p> Signup and view all the answers

    Which of the following is NOT a component of the cell cortex in red blood cells?

    <p>Glycogen (C)</p> Signup and view all the answers

    What is the main role of the glycocalyx in the cell membrane?

    <p>To facilitate cell-to-cell communication and recognition. (D)</p> Signup and view all the answers

    Which of the following is a major lipid component of the plasma membrane?

    <p>Phosphatidylcholine (B)</p> Signup and view all the answers

    What is the structural characteristic of phospholipids that allows them to form a bilayer in the plasma membrane?

    <p>They are hydrophilic and hydrophobic. (B)</p> Signup and view all the answers

    Which feature of the cell membrane is responsible for its selective permeability, allowing only certain molecules to pass through?

    <p>The presence of integral and peripheral proteins. (B)</p> Signup and view all the answers

    Hereditary spherocytosis is a genetic disease caused by dysfunction in the function of which type of proteins?

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

    What is the primary cause of the symptoms associated with hereditary spherocytosis, such as fatigue, dizziness, and hair loss?

    <p>Reduced oxygen-carrying capacity due to abnormal red blood cell shape. (B)</p> Signup and view all the answers

    Flashcards

    Lipid Bilayer

    A structure formed by phospholipids with hydrophilic heads facing water and hydrophobic tails shielded from it.

    Hydrophilic Heads

    The part of phospholipids that is attracted to water, facing the aqueous environment.

    Hydrophobic Tails

    The non-polar part of phospholipids that repels water, located inside the bilayer.

    Cytosolic Monolayer

    The layer of the lipid bilayer that faces the cytosol inside the cell.

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    Non-Cytosolic Monolayer

    The layer of the lipid bilayer that faces the external environment of the cell.

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    Plasma Membrane Fluidity

    The characteristic of the plasma membrane that allows lipids and proteins to move freely within it.

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    Asymmetrical Distribution

    The non-uniform arrangement of phospholipids and glycolipids between the monolayers.

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    Factors Affecting Fluidity

    Key elements that influence how fluid a plasma membrane is, such as temperature, lipid composition, and tail length.

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    Phosphatidylethanolamine

    A phospholipid component of cell membranes, often present in the inner leaflet.

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    Plasma membrane asymmetry

    The distinct distribution of lipids and proteins in the inner and outer layers of the membrane.

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    Vesicle budding

    The process of membrane transport where vesicles form from the Golgi apparatus.

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    Integral membrane proteins

    Proteins that span the membrane and can be transmembrane or lipid-linked.

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    Transmembrane proteins

    Proteins that cross the lipid bilayer, often forming α-helices.

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    Lateral movement of proteins

    The ability of membrane proteins to move within the lipid bilayer.

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    Cell cortex binding

    The restriction of proteins to specific areas by linking to the cell's cytoskeleton.

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    Membrane fluidity visualization

    The method to observe protein movement in membranes by staining.

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    Hereditary spherocytosis

    A genetic disease resulting in abnormal red blood cells that are spherical and less flexible, causing hemolytic anemia.

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    Biconcave shape

    The natural disc-like shape of red blood cells, allowing flexibility and passage through capillaries.

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    Hemolytic anemia

    A condition characterized by the destruction of red blood cells faster than they can be made, leading to symptoms like fatigue and dizziness.

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    Cell cortex

    A meshwork of proteins in red blood cells that maintains their shape, including spectrin and ankyrin.

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    Glycocalyx

    A sugar coating formed by carbohydrates attached to plasma membrane proteins and lipids, providing protection and recognition.

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    Phospholipids

    Major components of cell membranes that have a hydrophilic head and a hydrophobic tail, forming a bilayer.

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    Amphipathic molecules

    Molecules with both hydrophilic (water-attracting) and hydrophobic (water-repelling) parts, typical of membrane lipids.

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    Phosphatidylcholine

    The most common phospholipid in biological membranes, essential for membrane structure and function.

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    Tight Junctions

    Connections between epithelial cells that prevent mixing of membrane proteins.

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    Cell Membrane Functions

    Involves cell signaling, transport, growth, recognition, and adhesion.

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    Lipid Bilayer Fluidity

    The lipid bilayer is dynamic, allowing movement of its components.

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    Integral vs. Peripheral Proteins

    Integral proteins span the membrane; peripheral proteins are attached to its surface.

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    Phospholipid Asymmetry

    Phospholipids are distributed unevenly across the bilayer, affecting membrane properties.

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    Cell-Cell Adhesion

    Process by which cells stick together, crucial for tissue formation.

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    Study Notes

    Cell Membrane Structure and Composition

    • The cell membrane is a phospholipid bilayer, composed of phospholipid molecules.
    • Phospholipids have a hydrophilic head and two hydrophobic tails.
    • The hydrophilic heads face the extracellular fluid and cytoplasm, while the hydrophobic tails face each other in the interior of the membrane.
    • Cholesterol and glycolipids are also components of the cell membrane.
    • Proteins are embedded in the membrane, and are either integral or peripheral.
    • Integral proteins span the entire membrane, while peripheral proteins are only on one side of the membrane.
    • Carbohydrates are attached to proteins (glycoproteins) and lipids (glycolipids), and face the extracellular fluid.
    • This carbohydrate layer is called the glycocalyx.
    • The cell membrane's structure as a fluid mosaic model: A flexible sheet composed of lipids and proteins.
    • The membrane is composed of a fluid phospholipid bilayer with proteins embedded within it that have various functions.

    Hereditary Spherocytosis

    • Hereditary spherocytosis is a genetic disorder causing hemolytic anemia.
    • It's characterized by red blood cells losing their biconcave shape, becoming spherical, and unable to flow through narrow capillaries efficiently.
    • It leads to symptoms like fatigue, dizziness, hair loss, and yellowing of the eyes.
    • The disease results from dysfunctional proteins (like spectrin and ankyrin) that attach the cell membrane to its cytoskeleton.

    Red Blood Cell Membrane Structure

    • Red blood cell membranes are supported by a protein framework called the cell cortex comprised of actin, myosin, and proteins like spectrin and ankyrin.
    • The membrane itself is a thin film of fatty lipids and proteins.
    • Carbohydrates are attached to the lipids and proteins on the outer surface, forming the glycocalyx.

    All Plasma Membranes

    • All plasma membranes, surrounding the cell or organelles, consist of lipids and proteins.
    • Membrane lipids are arranged in two sheets, called a lipid bilayer.

    Plasma Membrane Lipids

    • The primary lipids in the plasma membrane are phospholipids, cholesterol, and glycolipids.
    • Phospholipids are amphipathic, with a hydrophilic head and hydrophobic tails.
    • The arrangement of the hydrophilic heads and hydrophobic tails cause the formation of the bilayer, shielding the hydrophobic tails from the surrounding water.
    • Cholesterol and glycolipids further contribute to membrane properties.

    Phosphatidylcholine

    • Phosphatidylcholine is the predominant phospholipid in biological membranes.
    • Its hydrophilic head comprises a choline molecule and a phosphate group.
    • The hydrophobic tails are composed of fatty acids.
    • These tails can be saturated or unsaturated, affecting overall membrane fluidity.

    Phospholipid Bilayer

    • The hydrophilic heads of the phospholipids face outward, interacting with water on both sides of the membrane.
    • The hydrophobic tails face inward, shielded from water.
    • This arrangement forms a stable, sealed compartment.

    Membrane Protein Types

    • Integral proteins are embedded within the lipid bilayer, often spanning it completely.
    • Peripheral proteins are loosely attached to the surface of the membrane.

    Transmembrane Proteins

    • Transmembrane proteins usually traverse the lipid bilayer as an alpha helix.
    • The polypeptide backbone is hydrophilic, allowing it to interact with water.
    • Hydrophobic amino acid side chains interact with the lipid bilayer's hydrophobic core.

    Membrane Protein Movement

    • Membrane proteins can move laterally within the lipid bilayer.
    • The movement is restricted by interactions with other cell components.

    Carbohydrates on the Cell Membrane

    • Carbohydrates are attached to membrane proteins (glycoproteins) and lipids (glycolipids).
    • These carbohydrates form the glycocalyx on the outer surface of the cell membrane.
    • The glycocalyx plays a role in cell recognition and adhesion.

    Cell Adhesion

    • The glycocalyx allows for cell-cell adhesion through interactions between carbohydrate regions.

    Plasma Membrane Functions

    • The cell membrane is involved in cell signaling, transport, cell growth and motility, cell-cell recognition, and intercellular adhesion.
    • Membrane proteins have specific roles in these functions.

    Membrane Fluidity

    • Temperature, lipid composition (including cholesterol), and saturation degree impact membrane fluidity.

    Membrane Protein Synthesis and Transport

    • Membranes are synthesized in the smooth endoplasmic reticulum.
    • Phospholipids are added to the cytosolic side.
    • The Golgi apparatus further modifies the membrane and distributes phospholipids asymmetrically.

    Membrane Asymmetry

    • The distribution of lipids and proteins within the membrane is not even, leading to membrane asymmetry.

    Membrane Protein Movement

    • Staining membrane proteins allows observation of protein movement.
    • Movement may be restricted by factors, such as binding to the cytoskeleton or extracellular matrix.

    Learning Outcomes

    • Understanding the structure, location, and function of the cell cortex.
    • Explaining the formation of the lipid bilayer and its characteristics as fluid and asymmetrical.
    • Listing membrane components, explaining their movement, and mechanisms regulating it.
    • Visualizing cell membrane structures depicting phospholipids and protein types, and showing membrane asymmetry.
    • Predicting the effects of component removal or inhibition.
    • Explaining cell fusion experiments and results.
    • Classifying transmembrane proteins based on structure.
    • Describing how polypeptide chains span the hydrophobic lipid bilayer interior.
    • Detailing new membrane synthesis and phospholipid asymmetry.
    • Explaining membrane orientation maintenance.
    • Defining the glycocalyx, its structure and function in tissue formation.

    Keywords for Studying the Lecture

    • Amino acids (hydrophobic, hydrophilic, polar, nonpolar)
    • Lipids (polar, nonpolar)
    • Charges (partial positive, partial negative)
    • Bonds (covalent)
    • Molecular structure (primary, secondary)

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    Cell Membrane Structure and Composition PDF

    Description

    This quiz covers the key features of the cell membrane, including its phospholipid bilayer structure and the roles of embedded proteins. Explore the functions of cholesterol, glycolipids, and glycoproteins within the membrane, as well as the fluid mosaic model concept. Test your understanding of how these components contribute to cell function.

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