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Questions and Answers

Which of the following proteins is categorized as a peripheral membrane protein?

  • Band 3
  • Spectrin
  • Stomatin
  • Actin (correct)

    • What is the primary function of the erythrocyte cytoskeleton?

  • Protein synthesis
  • Maintain cell integrity (correct)
  • Oxygen transport
  • Energy production

    • What percentage of skeletal mass in red cells does spectrin constitute?

  • 10% to 20%
  • 50% to 75% (correct)
  • 25% to 50%
  • 75% to 90%

    • Which gene encodes for alpha spectrin?

    <p>Chromosome 1</p> Signup and view all the answers

    Spectrin was first discovered in which decade?

    <p>1960s</p> Signup and view all the answers

    What is the composition of actin protofilaments?

    <p>14 monomers each</p> Signup and view all the answers

    Which of the following proteins is involved in the interaction of actin towards the ends of spectrin rods?

    <p>Band 4.1 molecule</p> Signup and view all the answers

    What role do adaptor proteins serve in the spectrin-actin network?

    <p>Attachment of the spectrin-actin network to biological membrane</p> Signup and view all the answers

    What type of actin is involved in the dynamic equilibrium within the cell?

    <p>G-actin</p> Signup and view all the answers

    Which of the following is a type of adaptor protein mentioned in the context?

    <p>Ankyrin (band 4.9)</p> Signup and view all the answers

    What is the primary function of carbohydrates in biological membranes?

    <p>Locking the orientation of proteins in the membrane</p> Signup and view all the answers

    Which component of biological membranes is least abundant?

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

    What percentage of biological membranes is made up of lipids?

    <p>40%</p> Signup and view all the answers

    What type of membrane proteins are mainly found on the extracellular surface?

    <p>Peripheral membrane proteins</p> Signup and view all the answers

    What is NOT a function of carbohydrates in biological membranes?

    <p>Energy storage</p> Signup and view all the answers

    What is the primary function of Band 4.1 in red blood cells?

    <p>Stabilize the membrane by linking the spectrin-actin cytoskeleton to the lipid bilayer</p> Signup and view all the answers

    How many copies of Band 4.1 are present in each red blood cell?

    <p>200,000</p> Signup and view all the answers

    What condition is associated with a deficiency of Band 4.1?

    <p>Hereditary elliptocytosis</p> Signup and view all the answers

    What essential role does Ankyrin play in red blood cells?

    <p>Attachment of the spectrin-actin cytoskeletal network to the plasma membrane</p> Signup and view all the answers

    What is the significance of maintaining deformability in erythrocytes?

    <p>Enhances passage through capillary beds without lysis</p> Signup and view all the answers

    What is a characteristic shape of erythrocytes in hereditary spherocytosis?

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

    Which of the following symptoms is NOT typically associated with hereditary spherocytosis?

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

    What laboratory feature is commonly observed in patients with hereditary spherocytosis?

    <p>Normal hemoglobin levels</p> Signup and view all the answers

    Which of the following does NOT describe a normal red blood cell?

    <p>Lacks central pallor</p> Signup and view all the answers

    What is a distinguishing feature of spherocytes compared to normal red blood cells?

    <p>Circular shape</p> Signup and view all the answers

    What is the basic functional unit of the spectrin network?

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

    Which protein is NOT involved in linking the spectrin network to the plasma membrane?

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

    What role does the spectrin-actin network play in erythrocytes?

    <p>Maintains structural integrity</p> Signup and view all the answers

    What form of actin is known as the monomeric form?

    <p>G-actin</p> Signup and view all the answers

    Why is the dynamic nature of the spectrin-actin network important?

    <p>It enables cells to deform without rupturing.</p> Signup and view all the answers

    What is the primary consequence of mutations in spectrin leading to decreased structural integrity of RBCs?

    <p>Formation of spherical RBCs</p> Signup and view all the answers

    Which protein is primarily responsible for anchoring spectrin to the RBC membrane?

    <p>Band 3</p> Signup and view all the answers

    What percentage of hereditary spherocytosis cases is attributed to ankyrin deficiencies?

    <p>50% - 67%</p> Signup and view all the answers

    Which type of spectrin defect is associated with the most severe form of hereditary spherocytosis?

    <p>Alpha-spectrin defects</p> Signup and view all the answers

    What structural change occurs in red blood cells due to spectrin mutations?

    <p>RBCs lose their deformability</p> Signup and view all the answers

    What is a key characteristic of peripheral membrane proteins?

    <p>Bound to the surface of membranes temporarily</p> Signup and view all the answers

    What distinguishes integral membrane proteins from peripheral membrane proteins?

    <p>Interact with both sides of the lipid bilayer</p> Signup and view all the answers

    Which method is commonly used to release proteins from erythrocyte ghost membranes?

    <p>High ionic strength medium</p> Signup and view all the answers

    What is a function of integral membrane proteins in the lipid bilayer?

    <p>Signal transduction</p> Signup and view all the answers

    Which of the following best describes the extraction process for peripheral membrane proteins?

    <p>Involves changing pH or ionic strength</p> Signup and view all the answers

    What is the primary role of Band 3 in red blood cells?

    <p>Anion exchange and cytoskeletal anchoring</p> Signup and view all the answers

    Which gene is responsible for encoding Band 3 in red blood cells?

    <p>SLC4A1</p> Signup and view all the answers

    What percentage of hereditary spherocytosis (HS) mutations are attributed to defects in Band 3?

    <p>15 - 20%</p> Signup and view all the answers

    What type of mutations are associated with hereditary elliptocytosis?

    <p>Mutations in spectrin molecules</p> Signup and view all the answers

    How do mutations in the SLC4A1 gene affect red blood cells?

    <p>They disrupt the function of Band 3 and interaction with the cytoskeleton.</p> Signup and view all the answers

    Study Notes

    Major Erythrocyte Membrane Proteins

    • Peripheral proteins include Actin, Adducin, Ankyrin, Dermatin, G3PD, Protein 4.1, Spectrin, and Tropomyosin.
    • Integral proteins consist of Band 3 and Stomatin, among others.

    Cytoskeleton (Membrane Skeleton)

    • Comprises structural protein filaments, providing support and facilitating transport and cellular processes.
    • Major components: Spectrin and Actin.
    • Spectrin accounts for 50%-75% of the erythrocyte cytoskeleton, discovered in the 1960s.

    Actin

    • Assembles into stable protofilaments, vital for the dynamic equilibrium of G-actin and F-actin.
    • Enables rapid assembly/disassembly in response to cellular requirements.

    Spectrin Network

    • Spectrin tetramers link actin filaments, maintained by adaptor proteins like Band 4.1 and Adducin.
    • Integrates the cytoskeletal network with the cell membrane, crucial for RBC integrity.

    Biological Membrane Composition

    • Major components: Lipid bilayer (40%) and Proteins (60%).
    • Minor components: Carbohydrates (1-10%), primarily attached to proteins and lipids, involved in molecular recognition and stability.

    Band 4.1

    • Stabilizes the spectrin-actin cytoskeleton's attachment to the lipid bilayer.
    • Approximately 200,000 copies in each red cell; essential for RBC flexibility and integrity.

    Ankyrin (Band 4.9)

    • Links spectrin-actin network to the plasma membrane, ensuring structural stability.
    • Binds to integral membrane proteins aiding in RBC resilience during circulatory stress.

    Importance of Erythrocyte Cytoskeleton

    • Maintains erythrocyte deformability, crucial for passing through capillaries without fracturing.

    Hemolytic Anemia Overview

    • Characterized by premature destruction of RBCs.
    • Types include Hereditary Spherocytosis (spherical RBCs) and Hereditary Elliptocytosis (elliptical RBCs).

    Hereditary Spherocytosis (HS)

    • Often detected in infancy; signs include anemia, jaundice, and splenomegaly.
    • Lab findings show reticulocytosis, hyperbilirubinemia, and hallmark spherocytes, distinctive in shape and size.

    Normal vs. Spherocytes

    • Normal RBCs: Biconcave shape, maneuverable, and capable of expanding in hypotonic environments.
    • Spherocytes: Circular, reduced surface area, rigid and unable to maneuver effectively.

    Dynamic Spectrin Network

    • Remodeling allows erythrocytes to withstand mechanical stresses without rupturing, vital for microvascular circulation.

    Proteins in RBC Membrane

    • Comprise around 20 major and over 300 minor proteins crucial for erythrocyte function.
    • Protein extraction enhanced by high ionic strength or pH changes.

    Spectrin Deficiency in HS

    • Mutations affect spectrin structure, disrupting the network, leading to spherical RBCs that are prone to rupture.
    • Deficiencies vary between α-spectrin and β-spectrin.

    Ankyrin Deficiency in HS

    • Mutations in ANK1 affect the anchoring of spectrin to the RBC membrane.
    • Contributes to spherocyte formation and increased fragility, responsible for a significant portion of HS cases.

    Band 3 Defects

    • Integral to anion exchange and cytoskeletal anchoring; mutations disrupt RBC membrane integrity.
    • Defects account for a notable percentage of HS mutations.

    Hereditary Elliptocytosis (HE)

    • Associated with spectrin defects affecting the ability to form heterotetramers, resulting in fragile, elliptical cells.

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    Description

    This quiz explores the key peripheral and integral proteins found in erythrocyte membranes, detailing their molecular weights and functions. Test your knowledge on proteins such as Spectrin, Band 3, and more, while understanding their significance in cellular architecture.

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