36. The ABO(H) system. Biosynthesis of ABO(H) and Lewis antigens.

Question 1

The ABO(H) systems

Answer 1

Nature:
-Type: Oligosaccharides on glycolipids and glycoproteins.
-Location: Part of the cell glycocalyx.

Structure:
-Core Oligosaccharide: Common base structure.
-Antigenic Determinants: One or two added monosaccharides distinguishing blood groups.

H Blood Group System:
-Enzymes: Glycosyltransferases synthesize A, B, and H antigens.
-Precursor: Common oligosaccharide ending with galactose.
-Antigen H: Formed by adding fucose via fucosyltransferase (encoded by H/FUT1 gene).
-Bombay Phenotype: hh homozygotes lack antigen H, carrying only the precursor.

Question 2

Biosynthesis of ABO(H)

Answer 2

Alleles: A, B, and O.
-A and B Alleles: Encode transferase A and transferase B.
-O Allele: Does not encode an active protein.
-Substrate: Both transferases use H antigen.
–Transferase A: Adds N-acetylgalactosamine, creating A antigen.
–Transferase B: Adds galactose, creating B antigen.