Membranes and Receptors Module

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Questions and Answers

What role do carbohydrate groups play in integral proteins like bands 3 and 7?

They lock the orientation of the protein in the membrane. (correct)

They increase the solubility of proteins in the cytoplasm.

They enhance the electrical conductivity of the cell membrane.

They facilitate the rotation of proteins within the membrane.

What is the primary protein structure that forms the erythrocyte cytoskeleton?

Keratin

Collagen

Myosin

Spectrin (correct)

Which of the following statements about Hereditary Spherocytosis is accurate?

It leads to decreased resistance to lysis during capillary passage. (correct)

It results in normal spectrin levels.

It causes increased red blood cell deformability.

It is characterized by elongated red blood cells.

The erythrocytes in Hereditary Elliptocytosis are fragile mainly because:

Spectrin fails to form heterotetramers. Signup and view all the answers

What is the function of ankyrin in the cytoskeleton of red blood cells?

To link spectrin to integral membrane proteins. Signup and view all the answers

How does the attachment of integral membrane proteins to the cytoskeleton affect their mobility?

It restricts the lateral mobility of membrane proteins. Signup and view all the answers

What consequence arises due to the structure of the spectrin-actin network in erythrocytes?

Maintenance of red blood cell deformability. Signup and view all the answers

What characterizes integral membrane proteins?

They interact extensively with the hydrophobic regions of the lipid bilayer. Signup and view all the answers

Which of the following is NOT a component that links to the erythrocyte cytoskeleton?

Hemoglobin Signup and view all the answers

Why is the asymmetrical orientation of membrane proteins important?

It enables receptors to interact correctly with extracellular signals. Signup and view all the answers

How can peripheral proteins be distinguished from integral proteins in erythrocyte ghosts?

Peripheral proteins are removed by high ionic strength conditions. Signup and view all the answers

What is the lipid mosaic theory?

It states that proteins are embedded irregularly in a fluid lipid bilayer. Signup and view all the answers

Which method is used to analyze erythrocyte ghost membranes?

Gel electrophoresis. Signup and view all the answers

What happens to peripheral proteins when the pH is altered?

They can be extracted from the membrane. Signup and view all the answers

What type of molecule must an extracellular messenger receptor direct towards the extracellular space?

Hydrophilic molecules. Signup and view all the answers

Which proteins are typically susceptible to proteolysis only when the cytoplasmic face is accessible?

Peripheral proteins. Signup and view all the answers

Study Notes

Membranes and Receptors Module - Session 1, Lecture 1.2 - Proteins of Cell Membrane

The lecture is about proteins of cell membranes.
The objectives include understanding the distribution and role of proteins in membrane structure, the importance of asymmetrical distribution of membrane proteins, and the structure of the erythrocyte cytoskeleton.

Lipid Mosaic Theory of Membrane Structure

Biological membranes are composed of a lipid bilayer with associated proteins.
Proteins can be peripheral or integral.
Peripheral proteins are bound to the membrane surface by electrostatic and hydrogen bonds, and can be removed by changes in pH or ionic strength.
Integral proteins are deeply embedded within the hydrophobic regions of the lipid bilayer, requiring detergents or organic solvents for removal.

Fluid Mosaic Model

The model depicts the arrangement of phospholipids and proteins within the membrane structure.
Integral proteins are depicted as traversing the lipid bilayer, while peripheral proteins are positioned on the membrane's surface.
The model highlights the fluid nature of membranes, allowing for protein and lipid movement.

Importance of Asymmetrical Distribution of Membrane Proteins

Asymmetrical protein orientation is crucial for membrane function.
Examples: receptors for hydrophilic extracellular messengers (e.g., insulin) require their recognition sites to face the extracellular space.
This precise arrangement allows for proper signal transduction and cellular response.

Erythrocyte Cytoskeleton

The erythrocyte cytoskeleton provides structural support and maintains the cell's shape.
It is a network of spectrin and actin molecules.
Spectrin is a long, floppy rod-like molecule composed of alpha and beta subunits.
These subunits form heterodimers that associate to create a heterotetramer (alpha2beta2).
Spectrin-actin networks connect to the membrane through adapter proteins (ankyrin, band 4.1, adducin).

Composition of Red Blood Cell (RBC) Membrane

RBC membranes are composed of:
- 50% protein
- 20% phospholipid
- 20% cholesterol
- 10% carbohydrate

Distinguishing Peripheral and Integral Proteins

Peripheral proteins are released when ghost membranes are treated with high ionic strength media or pH changes.
Integral proteins (e.g., bands 3 and 7) require detergents to dissociate from the membrane.
Peripheral proteins are located on the cytoplasmic face of the membrane, as they are accessible to proteolysis there.

Glycoproteins and Membrane Stability

Many membrane proteins are glycoproteins, possessing covalently linked carbohydrate units.
Extracellular carbohydrate groups are highly hydrophilic, contributing to membrane stability by preventing flip-flop rotation of the proteins.
These carbohydrate units also play a role in cellular recognition and immune reactions.

Haemolytic Anemias

RBC cytoskeleton is essential for maintaining deformability during capillary passage without hemolysis.
Hereditary spherocytosis involves reduced spectrin levels, resulting in spherocytes and premature erythrocyte destruction (hemolysis).
Hereditary elliptocytosis involves spectrin abnormalities leading to fragile elliptoid cells.

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Description

This quiz covers the proteins of cell membranes, focusing on their distribution, roles, and the structure of the erythrocyte cytoskeleton. It delves into the lipid mosaic theory and fluid mosaic model, explaining the distinctions between peripheral and integral proteins. Test your understanding of the fundamental concepts of membrane structure and dynamics.