Red Cell Membrane Structure and Function

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Questions and Answers

What is the primary function of red blood cells?

To transport respiratory gases to/from tissues (correct)

To fight off infections

To produce hormones

To regulate body temperature

What is the average lifespan of red blood cells in the blood circulation?

240 days

180 days

60 days

120 days (correct)

What is the composition of the red cell membrane?

44% lipid and 56% protein (correct)

55% lipid and 45% protein

70% lipid and 30% protein

60% lipid and 40% protein

What is the function of the glycocalyx in the red cell membrane?

To provide a site for membrane surface receptors Signup and view all the answers

Why is the red cell membrane required to be tough but flexible and show deformability?

To function in microcirculation Signup and view all the answers

What is the role of haemoglobin in red blood cells?

To enable oxygen delivery to the tissues Signup and view all the answers

What is the result of a reduced lifespan of red blood cells?

Haemolytic anaemia Signup and view all the answers

Where do red blood cells develop?

In the bone marrow Signup and view all the answers

What is the percentage of protein in the red cell membrane?

49% Signup and view all the answers

What is the main function of the Band 3 protein in the red cell membrane?

Facilitates anion transport across the membrane Signup and view all the answers

What is the primary function of glycophorins in the red cell membrane?

Act as binding sites for viruses, bacteria, and parasites Signup and view all the answers

What is the percentage of carbohydrate in the red cell membrane?

7% Signup and view all the answers

What is the primary function of the glucose transport protein in the red cell membrane?

Facilitates glucose transport across the membrane Signup and view all the answers

What is the primary function of spectrin in the red cell membrane?

Associates with ankyrin, band 4.1, actin, and anionic phospholipids Signup and view all the answers

What is the primary function of ankyrin in the red cell membrane?

Anchors spectrin molecules to the lipid bilayer Signup and view all the answers

What is the arrangement of subunits in spectrin?

Anti-parallel arrangement Signup and view all the answers

What is the function of Band 4.1 in the cytoskeleton?

Binds to spectrin close to the actin binding site Signup and view all the answers

What is the function of Ankyrin in the cytoskeleton?

Anchors spectrin molecules to the lipid bilayer Signup and view all the answers

What is the function of Actin in the cytoskeleton?

Polymerizes to form filaments Signup and view all the answers

What is the function of Spectrin in the cytoskeleton?

Associates with Ankyrin, band 4.1, actin & anionic phospholipids Signup and view all the answers

What is the function of the Glucose Transport Protein (GLUT 1)?

Transports glucose molecules Signup and view all the answers

What is the function of Glycophorin A?

Binds to Band 4.1 Signup and view all the answers

What is the function of the Red Cell Na+/K+ ATPase?

Transports Na+ and K+ ions Signup and view all the answers

What is the result of each ATP hydrolysis by the Red Cell Na+/K+ ATPase?

Removes 3 Na+ and transports 2 K+ Signup and view all the answers

What is transported out of the cell during the release of the pump?

3 NA+ molecules Signup and view all the answers

What is the function of Ankyrin in the peripheral proteins of the cytoskeleton?

To anchor spectrin molecules to the lipid bilayer Signup and view all the answers

What is the shape of the cells in Hereditary Elliptocytosis?

Oval or elliptical Signup and view all the answers

Which protein binds to spectrin close to the actin binding site?

Band 4.1 Signup and view all the answers

What is the result of defective/deficiency of skeletal proteins in Hereditary Spherocytosis?

Spherocytosis and haemolytic anaemia Signup and view all the answers

What is the characteristic of cells in Rh Null Syndrome?

Stomatocytosis and spherocytosis Signup and view all the answers

Which of the following is NOT a characteristic of Primary Membrane Disorders?

Increased life-span of red cells Signup and view all the answers

Which protein is mainly affected in Hereditary Spherocytosis?

Spectrin Signup and view all the answers

Study Notes

Red Blood Cells

Also known as erythrocytes, they have a bi-concave disc shape
Their role is to transport respiratory gases to and from tissues, specifically delivering oxygen to tissues and removing waste products of metabolism
On average, a healthy adult male has 5,000,000,000,000 red blood cells per liter of blood

Red Cell Facts

Red blood cells develop in the bone marrow but lose their nucleus by the time they reach the bloodstream
They contain hemoglobin, which enables oxygen delivery to tissues
Red blood cells have an average lifespan of 120 days in the blood circulation, and a reduced lifespan can lead to hemolytic anemia

Function of Red Cell Membrane

The membrane must be tough but flexible and show deformability to function in microcirculation
This is achieved by the interaction of a protein cytoskeleton with the membrane lipid bilayer
The main functions of the red cell membrane are:
- Separating the cell contents from the plasma
- Maintaining the characteristic shape of the cell
- Regulating intracellular cat ion concentrations
- Serving as a site for membrane surface receptors

The Red Cell Membrane

Composed of an outer glycocalyx carbohydrate 'coat', a lipid bilayer, and a framework of peripheral proteins that comprise the red cell cytoskeleton
The glycocalyx is made up of both extracellular proteins and glycosylated proteins and lipids from the lipid bilayer
The lipid bilayer is made up of 44% lipid, which acts as a permeability barrier and comprises a basic phospholipid bilayer
The protein component is 49% of the membrane, comprising integral and peripheral proteins that provide skeletal structure and selective transport across the membrane
The carbohydrate component is 7% of the membrane, associated with proteins or lipids, and presented on the outside of the membrane

Composition of the Red Cell Membrane

Membrane lipids:
- 30% cholesterol
- 60% phospholipid (phosphatidyl choline, sphingomyelin, phosphatidyl ethanolamine, phosphatidyl serine)
- 10% glycerides/FFA
Integral proteins:
- Band 3: facilitates anion transport across the membrane, binding site for skeletal and other red cell proteins
- Glycophorins (A, B, C, D, E): sialoglycoproteins providing negative charge, acting as binding sites for viruses, bacteria, and parasites, and required for structural integrity of the red cell
- Glucose Transport Protein: 12 trans-membrane domains, surface concentration varies
- Rh Proteins: associated into a macrocomplex, transport function, and interact with the cytoskeleton

Peripheral Proteins of the Cytoskeleton

Spectrin: subunits bind in an anti-parallel arrangement, associates with ankyrin, band 4.1, actin, and anionic phospholipids
Ankyrin: found in 2 forms, anchors spectrin molecules to the lipid bilayer
Actin: globular protein that polymerizes readily to form filaments, binds weakly to the tail end of spectrin and holds together in a 2D lattice
Band 4.1: globular protein that binds to spectrin close to the actin binding site, binds directly to glycophorins A & C, Band 3, phosphatidyl serine, and ankyrin

Red Cell Na+/K+ ATPase 'Cation Pump'

Enzyme composed of 3 protein subunits, catalyzes the conversion of ATP to ADP to release energy
ADP formed is reconverted to ATP by the EM Pathway
Each ATP hydrolyzed removes 3 Na+ molecules and subsequently transports 2 K+ into the cell

Mechanism of Na+/K+ ATPase 'Pump'

Phosphorylation (energy release) of the pump transports out 3 Na+ molecules
Dephosphorylation transports 2 K+ into the cell

Primary Membrane Disorders

Inherited disorders of the red cell membrane
Affects cell shape, reduced life-span can lead to compensated anemia
Examples:
- Hereditary Spherocytosis: autosomal inheritance, results in defective/deficiency of skeletal proteins (mainly spectrin), causes spherocytosis and hemolytic anemia
- Hereditary Elliptocytosis: presence of a large proportion of oval or elliptical cells, defective spectrin, Band 4.1, or Band 3
- Rh Null Syndrome: absence of Rh Polypeptides and RhAG in the membrane, stomatocytosis and spherocytosis observed in peripheral blood, patient experiences compensated hemolytic anemia

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Description

Learn about the constituents of the red cell membrane, its function, and how its structure enables it to perform its function. Understand how the membrane works to maximize red cell lifespan.