~ 1J CHEMICAL CONNECTIONS 12D A, B, AB, and 0 Blood Types

Membranes of animal plasma cells have large numbers of relatively small carbohydrates bound to them. In fact, the outsides of most plasma cell membranes are literally II sugar-coated. II These mem­brane-bound carbohydrates are part of the mechanism by which cell types recognize one another and, in effect, act as biochemical markers. Typically, they contain from 4 to 17 monosaccharide units consisting primarily of relatively few monosaccharides, the most common of which are D-galactose, D-mannose, L-fucose, N-acetyl-D-glucosamine, and N-acetyl-D-galactosamine. L -Fucose is a 6-deoxyaldohexose.

CHO

HO H

H ----If----- 0 H An L-monosaccharide because this -OH group is on the left in the ~ H --+--- 0 H Fischer projection ~

H 0 -----1---- H /Carbon 6 is -CH3

C / rather than -CH20H

H3 L-Fucose

To see the importance of these membrane-bound carbohy­drates, consider the ABO blood group system, discovered in 1900 by Karl Landsteiner (1868-1943). Whether an individual belongs to

Bag of blood showing blood type.

u c

~-QJ

..c ~ ro QJ VI QJ

0::: o ...... o

..c CL

---

type A, B, AB, or 0 is genetically determined and depends on the type of trisaccharide or tetrasaccharide bound to the surface of the red blood cells. These surface-bound carbohydrates, designated as A, B, and 0, act as antigens. The type of glycosidic bond joining each monosaccharide is shown in the figure.

Type A N Acetyl (a-l ,4) (f3-1 ,3) - - ---D-Galactose N-Acetyl-D-glucosamine--+-

D-galactosamine

TypeB D-Galactose

Type 0

(a-l ,2)

L-Fucose

Red (a-l ,4) (f3-1 ,3) ---D-Galactose N -Acety 1-D-gI ucosamine ---I- blood

(a-l ,2) cell L-Fucose

G 1 (f3-1 ,3) All . D- a actose N- cety -D-g ucosamlne--+-

•

(a-l,2)

L-Fucose

The blood carries antibodies against foreign substances. When a blood carries B antigen (D-galactose) and has anti-A antibodies (against A antigens). Transfusion of type A blood into a person with type B blood can be fatal, and vice versa. The relationships between blood type and donor-receiver relationships are summa­rized in the figure.

person receives a blood transfusion, the antibodies clump together (aggregate) the foreign blood cells. Type A blood, for example, has A antigens (N-acetyl-D-galactosamine) on the surfaces of its red blood cells and carries anti-B antibodies (against B antigen). B-type

A, B, AB, and 0 Blood Types (continued)

Sugar on cell surface: A Has antibodies against: B Can receive blood from: A and ° Can donate blood to: A and AB

Sugar on cell surface: ° Has antibodies against: A and B Can receive blood from: ° Can donate blood to: 0, A, B, and AB

Type °

Type A

TypeAB

Type B

Sugar on cell surface: B Has antibodies against: A Can receive blood from: Band ° Can donate blood to: Band AB

Sugars on cell surface: A and B Has antibodies against: None Can receive blood from: 0, A, B, and AB Can donate blood to: AB

People with type 0 blood are universal donors, and those with type AB blood are universal acceptors. People with type A blood can accept blood from type A or type 0 donors only. Those with

type B blood can accept blood from type B or type 0 donors only. Type 0 persons can accept blood only from type 0 donors.