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How does the ABO gene produce different antigens on red blood cells?
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blood group
The major component of human blood is the red blood cell.
The ABO gene does not produce antigens directly; rather, it codes for specific glycosyltransferase enzymes that modify carbohydrate chains on the surface of red blood cells.
The process relies on a core precursor substance that must first be converted into the H antigen. The H gene produces an enzyme that adds l-fucose to this precursor. Once the H antigen is present, the ABO genes function as follows:
- A gene: Codes for an enzyme that adds N-acetyl-d-galactosamine to the H antigen, forming the A antigen.
- B gene: Codes for an enzyme that adds d-galactose to the H antigen, forming the B antigen.
If an individual lacks the functional A or B enzymes, the H antigen remains unmodified, resulting in type O blood. These antigens are typically found on glycolipid and glycoprotein molecules embedded in the red cell membrane.1