1. Red Blood Cell Membrane Structure

2. Red cell membrane • The red cell membrane consists of: Proteins~50% Lipids~43% Carbohydrates~7%

3. Certain blood group Ags are associated with specific membrane structures • Many Ags are proteins • Rhesus, Duffy, Kidd • Others are carbohydrates • ABO, Lewis, P • Others are a combination of glyolipids & proteins • M,N

4. Composition of the red cell membrane Carbohydrates • They occur only on the external surface of the red cell. • They are composed of glycoproteins and glycolipids.

5. Majority of monosaccharides on red cell membrane are six carbon sugar • In solution the six carbon atoms form a ring • The carbons are numbered around the ring from 1 - 6

6. Seven different mono-saccharides are present on the RBC membrane external surface • N-acetylneuraminic acid • Fucose • Glucose • Galactose • Mannose • N-acetylglucosamine • N-acetylgalactosamine (-ve charge)

7. Monosaccharides linkage • Monosaccharides are linked together by specific enzymes – glycosyltransferases • Each transferase catalyses the transfer of one sugar onto acceptor sugar • The enzyme is named according to the sugar that it transfers

8. Composition of the RBC memb. (cont.) Lipids • Lipid components of the red cell membrane are: • 60% Phospholipids • 30% cholesterol. • 10% sphingolipids.

9. Phospholipids Phosphate • Fatty acid tails • hydrophobic • Phosphate group head • hydrophilic • Arranged as a bilayer Fatty acid

10. Phospho-lipid bilayer

11. Composition of the red cell membrane Proteins • These are either: • Peripheral (can be removed without disturbing the membrane) • Integral, penetrating the lipid bilayer (removed if lipid bilayer is disturbed)-

12. Integral proteins

13. Peripheral Proteins • The red cell peripheral proteins interact to form a cytoskeleton. • The cytoskeleton acts as a tough supporting framework for the lipid bilayer. • Four peripheral proteins play a key role in the structure of the red cell cytoskeleton, these are : • Spectrin, which is the most abundant • Ankyrin • Protein 4.1 and • Actin

14. Spectrin • is the most abundant, consists of two chains, a and b, wound around each other • Spectrin gives the cell membrane its flexibility & strength • If denatured, red cell takes spherical shape and loses flexibility

15. Integral Proteins • These penetrate the lipid bilayer and are firmly anchored within it via interactions with the core. • Band 3 (acts as anion transport channel). • Glycophorins A, B, and C. • Na+/K+ ATPase. • glucose transport protein. • surface receptors. (the most important is the transferrin receptors).

16. Blood group antigens • Blood group antigens: are antigens found on the red cell membrane, they are responsible for the determination of the blood group of the individual. • Blood group antigens are found on both the protein and the carbohydrate components of the membrane glycoproteins and the glycolipids.

17. Defects of the red cell membrane • Defects of the proteins may explain some of the abnormalities of the shape of the red cell membrane, e.g. hereditary spherocytosis and elliptocytosis. • While alterations in lipid composition because of congenital or acquired abnormalities in plasma cholesterol or phospholipids may be associated with other membrane abnormalities, e.g. target cells and acanthocytes.