1-L2

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?

Chromosome 1 Signup and view all the answers

Spectrin was first discovered in which decade?

1960s Signup and view all the answers

What is the composition of actin protofilaments?

14 monomers each Signup and view all the answers

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

Band 4.1 molecule Signup and view all the answers

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

Attachment of the spectrin-actin network to biological membrane Signup and view all the answers

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

G-actin Signup and view all the answers

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

Ankyrin (band 4.9) Signup and view all the answers

What is the primary function of carbohydrates in biological membranes?

Locking the orientation of proteins in the membrane Signup and view all the answers

Which component of biological membranes is least abundant?

Carbohydrates Signup and view all the answers

What percentage of biological membranes is made up of lipids?

40% Signup and view all the answers

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

Peripheral membrane proteins Signup and view all the answers

What is NOT a function of carbohydrates in biological membranes?

Energy storage Signup and view all the answers

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

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

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

200,000 Signup and view all the answers

What condition is associated with a deficiency of Band 4.1?

Hereditary elliptocytosis Signup and view all the answers

What essential role does Ankyrin play in red blood cells?

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

What is the significance of maintaining deformability in erythrocytes?

Enhances passage through capillary beds without lysis Signup and view all the answers

What is a characteristic shape of erythrocytes in hereditary spherocytosis?

Spherical Signup and view all the answers

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

Leukocytosis Signup and view all the answers

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

Normal hemoglobin levels Signup and view all the answers

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

Lacks central pallor Signup and view all the answers

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

Circular shape Signup and view all the answers

What is the basic functional unit of the spectrin network?

Tetramer Signup and view all the answers

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

Myosin Signup and view all the answers

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

Maintains structural integrity Signup and view all the answers

What form of actin is known as the monomeric form?

G-actin Signup and view all the answers

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

It enables cells to deform without rupturing. Signup and view all the answers

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

Formation of spherical RBCs Signup and view all the answers

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

Band 3 Signup and view all the answers

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

50% - 67% Signup and view all the answers

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

Alpha-spectrin defects Signup and view all the answers

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

RBCs lose their deformability Signup and view all the answers

What is a key characteristic of peripheral membrane proteins?

Bound to the surface of membranes temporarily Signup and view all the answers

What distinguishes integral membrane proteins from peripheral membrane proteins?

Interact with both sides of the lipid bilayer Signup and view all the answers

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

High ionic strength medium Signup and view all the answers

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

Signal transduction Signup and view all the answers

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

Involves changing pH or ionic strength Signup and view all the answers

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

Anion exchange and cytoskeletal anchoring Signup and view all the answers

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

SLC4A1 Signup and view all the answers

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

15 - 20% Signup and view all the answers

What type of mutations are associated with hereditary elliptocytosis?

Mutations in spectrin molecules Signup and view all the answers

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

They disrupt the function of Band 3 and interaction with the cytoskeleton. 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.