1. Red Blood cell membrane

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 monosaccharides 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 Fatty acid tails Phosphate group head
hydrophobic
Phosphate group head
hydrophilic
Arranged as a bilayer
Fatty acid

10. Phospholipid 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.