Biochemistry of ABO Antigens

Summary

This video delves into the biochemical basis of the blood group system, explaining how different antigens form on the surface of red blood cells (RBCs). It clarifies that blood groups are determined by the presence of A, B, or both antigens, or the absence of any, resulting in the O blood group. The H antigen, present in all individuals, serves as a precursor for A and B antigens, with specific enzymes coded by the A and B alleles catalyzing their formation. The video also addresses the null alleles in O blood group individuals, which do not add to the H antigen, maintaining its original form.

Takeaways

• 🧬 The human blood group system is determined by the surface proteins, specifically antigens, present on red blood cells (RBCs).
• 🔍 There are four main blood groups: A, B, AB, and O, with the H antigen being a common precursor for A and B antigens.
• 🌐 The H antigen locus on chromosome 19 contains the fucosyltransferase gene, which is crucial for the formation of the H antigen.
• 🔬 Individuals with blood group O have null alleles, resulting in no additional molecules being added to the H antigen, leaving only the H antigen on RBCs.
• 📚 The H antigen is a basic structure consisting of a trisaccharide with fucose, galactose, and N-acetylglucosamine.
• 🧬 In individuals with blood group A, the A allele codes for an enzyme that adds a specific sugar to the H antigen, forming the A antigen.
• 🧬 For blood group B, the B allele produces an enzyme that modifies the H antigen to create the B antigen.
• 🔄 The process of blood group antigen formation involves specific enzymes transferring sugars to the H antigen precursor on the RBC surface.
• 🧬 The presence of A, B, or both A and B antigens on RBCs is determined by the expression of the respective alleles and the activity of their enzymes.
• 📝 The video script provides a biochemical explanation of how different blood group antigens are formed from a common precursor, the H antigen.
• 👍 The video encourages viewers to like and subscribe for more content on the topic.

Q & A

What is the primary determinant of an individual's blood group?

An individual's blood group is determined by the surface proteins, specifically the antigens present on the surface of red blood cells (RBCs).

What are the four main blood groups found in the human population?

The four main blood groups are A, B, AB, and O.

What is the significance of the H antigen in the context of blood groups?

The H antigen is significant as it acts as a precursor molecule for both A and B antigens and is present on the surface of RBCs in all individuals, regardless of their blood group.

What is the role of the FUT1 gene in the formation of blood group antigens?

The FUT1 gene codes for the α-1,2-fucosyltransferase enzyme, which is responsible for transferring fucose sugar from GDP-fucose to the oligosaccharide chain on the RBC surface, forming the H antigen.

How does the presence of the null allele affect the blood group of an individual?

The presence of the null allele in individuals with blood group O results in the production of a non-functional protein, which does not add any molecules to the precursor H antigen, leaving the RBCs with only the H antigen.

What enzyme does the A allele code for, and what is its function in blood group formation?

The A allele codes for an enzyme called GalNAc transferase or α1,3-N-acetylgalactosaminyltransferase, which catalyzes the transfer of N-acetylgalactosamine to form the A antigen from the H antigen.

What is the enzyme coded by the B allele, and how does it contribute to the formation of the B antigen?

The B allele codes for the enzyme called galactose transferase, which transfers galactose to the H antigen, catalyzing the formation of the B antigen.

What is the basic structure of the oligosaccharide molecule found on immature RBCs before any antigen addition?

The basic structure of the oligosaccharide molecule on immature RBCs consists of fucose, galactose, and N-acetylglucosamine.

How does the chromosome 19 contribute to the blood group system?

Chromosome 19 contains the H locus, which includes the FUT1 gene responsible for the production of the α-1,2-fucosyltransferase enzyme, essential for the formation of the H antigen.

What is the biochemical process that leads to the formation of A and B antigens from the H antigen?

The formation of A and B antigens from the H antigen involves the action of specific transferase enzymes coded by the A and B alleles, which catalyze the addition of N-acetylgalactosamine and galactose, respectively, to the H antigen.

Why do individuals with blood group AB have both A and B antigens on their RBCs?

Individuals with blood group AB have both A and B antigens on their RBCs because they express both the A allele, which codes for the enzyme to form the A antigen, and the B allele, which codes for the enzyme to form the B antigen.