~
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 sugar-coated. 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.
II
II
u
c
~-
CHO
QJ
..c
~
ro
QJ
HO
VI
H
QJ
0:::
o
......
o
..c
CL
H ----If----- 0 H
---
An L- monosaccharide
because this -OH group
is on the left in the ~
H --+--- 0 H
Fischer projection
~
H0
-----1----
H
/Carbon 6 is -CH3
/
rather than -CH 2 0H
Bag of blood showin g blood type.
C 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
Type A
N Acetyl
(a-l ,4)
---D-Galactose
D-galactosamine
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.
(f3-1 ,3)
N-Acetyl-D-glucosamine--+-
(a-l ,2)
L-Fucose
TypeB
D-Galactose
(a-l ,4)
- - - D-Galactose
(f3-1 ,3)
N -Acety1- D-gI ucosamine
---I-
(a-l ,2)
Red
blood
cell
L-Fucose
Type 0
D- G a 1actose
(f3-1 ,3)
lucosamlne--+.
N- A
cety l
-D-g
(a-l,2)
L-Fucose
•
The blood carries antibodies against foreign substances. When a
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
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.
A, B, AB, and 0 Blood Types (continued)
°
°
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
Sugar on cell surface: A
Has antibodies against: B
Can receive blood from: A and
Can donate blood to: A and AB
°
Type B
TypeAB
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.