1

Red Blood cell membrane

2

Red cell membrane

The red cell membrane consists of:

Proteins~50% Lipids~43% Carbohydrates~7%

CHO

Lipids

Proteins

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% Phospholipids30% cholesterol.10% sphingolipids.

9

Phospholipids

Fatty acid

Phosphate

Fatty acid tails hydrophobic

Phosphate group head hydrophilic

Arranged as a bilayer

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, and , 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.