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.

Outlines

00:00

🌟 Blood Group Biochemistry Introduction

This paragraph introduces the topic of the video, which is the biochemistry of the blood group system. It explains that an individual's blood group is determined by the surface proteins, or antigens, present on red blood cells (RBCs). The human population has four main blood groups: A, B, AB, and O. The script clarifies that the O blood group does not have any A or B antigens but does have the H antigen, which is a precursor for A and B antigens. The video promises to delve into the formation of these antigens from the H antigen through the action of specific enzymes.

🧬 The Structure and Formation of Blood Group Antigens

This paragraph delves into the biochemical processes that lead to the formation of different blood group antigens. It describes the immature RBCs, which have an oligosaccharide molecule on their surface, the basic structure of which is composed of fucose, galactose, and N-acetylglucosamine. The chromosome 19 contains the H locus, which includes the H gene responsible for the fucosyltransferase enzyme. This enzyme transfers fucose to the oligosaccharide chain, creating the H antigen. The paragraph then explains how different alleles (A and B) code for specific enzymes that modify the H antigen to form A and B antigens, respectively. The A allele produces an enzyme that adds an additional galactose, forming the A antigen, while the B allele produces an enzyme that modifies the fucose to form the B antigen.

🔬 Genetic Determinants of Blood Group Antigens

This paragraph discusses the genetic basis for the presence or absence of A and B antigens on RBCs. It explains that individuals with the O allele are homozygous for a null allele, which does not produce a functional protein to modify the H antigen, leaving it as the only antigen present. In contrast, individuals with the A or B alleles have functional enzymes that add specific sugars to the H antigen, resulting in the formation of A or B antigens. The paragraph also explains that individuals with both A and B alleles will have both A and B antigens on their RBCs due to the presence of both enzymes.

Keywords

💡Multiple Alleles

Multiple alleles refer to the presence of more than one variant of a gene that can be found at the same locus on homologous chromosomes. In the context of the video, this concept is used to explain the genetic diversity that leads to different blood types, such as A, B, AB, and O, within a population. The script mentions that the blood group system is determined by the presence of antigens on the surface of red blood cells (RBCs), which are influenced by the alleles inherited from parents.

💡Blood Group System

The blood group system is a classification of blood based on the presence or absence of inherited antigenic substances on the surface of red blood cells (RBCs). The video discusses the ABO blood group system, which includes types A, B, AB, and O. The system is crucial for blood transfusions, as matching blood groups is essential to prevent adverse reactions.

💡Antigens

Antigens are molecules, usually proteins, found on the surface of cells that can trigger an immune response when recognized by the immune system as foreign. In the video, antigens are the A and B substances present on the surface of RBCs, which determine a person's blood group. The presence or absence of these antigens is what differentiates one blood type from another.

💡Red Blood Cells (RBCs)

Red blood cells, or erythrocytes, are the most common type of blood cell and the vertebrate's principal means of delivering oxygen to the body tissues via hemoglobin. The video emphasizes that the type of antigen present on the surface of RBCs determines a person's blood group.

💡H Antigen

The H antigen is a precursor substance found on the surface of red blood cells that can be converted into either A or B antigens through the action of specific enzymes. The video explains that all individuals have the H antigen, which is crucial as it serves as the foundation for the development of A and B antigens.

💡Null Alleles

Null alleles are versions of a gene that do not produce a functional protein or product. In the script, individuals with type O blood are said to have null alleles, which means they do not produce A or B antigens, and only the H antigen is present on their RBCs.

💡Precursors

Precursors are substances that precede the formation of a product, often through a series of chemical reactions. In the context of the video, the H antigen is a precursor to both A and B antigens, undergoing enzymatic changes to form the specific antigens that determine blood type.

💡Fucosyltransferase

Fucosyltransferase is an enzyme that transfers a fucose molecule to another molecule, often a carbohydrate. In the video, the enzyme coded by the A allele, known as GalNAc transferase, is an example of a fucosyltransferase that catalyzes the formation of the A antigen from the H antigen.

💡Galactosyltransferase

Galactosyltransferase is an enzyme that transfers a galactose molecule to another molecule. The video describes how the B allele codes for an enzyme called galactosyltransferase, which is responsible for the conversion of the H antigen into the B antigen.

💡Oligosaccharide Chain

An oligosaccharide chain is a short chain of sugar molecules linked together. In the video, the immature RBCs have an oligosaccharide molecule on their surface that forms the basic structure for the H antigen before any antigenic determinants are added.

💡Chromosome 19

Chromosome 19 is one of the 23 pairs of human chromosomes and contains the gene locus responsible for the ABO blood group system. The video script mentions that the H locus on chromosome 19, which includes the FUT1 gene, plays a key role in the production of the H antigen.

Highlights

The video discusses the biochemistry of the blood group system, focusing on the formation of antigens on the surface of red blood cells (RBCs).

Blood groups are determined by the surface proteins present on RBCs, with four main types: A, B, AB, and O.

The H antigen is a precursor molecule for both A and B antigens and is present on the surface of all RBCs.

Individuals with blood group O have null alleles and do not produce any additional antigens beyond the H antigen.

The H antigen locus on chromosome 19 contains the H gene, which codes for a fucosyltransferase enzyme.

Fucosyltransferase transfers fucose sugar from GDP-fucose to the oligosaccharide chain on the RBC surface, forming the H antigen.

Blood group A individuals have the A allele, which codes for an enzyme that adds an N-acetyl-D-galactosamine to the H antigen to form the A antigen.

Blood group B individuals have the B allele, which codes for an enzyme that adds D-galactose to the H antigen to form the B antigen.

The A and B antigens are formed from the H antigen through the action of specific transferase enzymes.

The video explains the biochemical process behind the formation of A, B, and AB blood groups from the H antigen.

Individuals expressing both A and B alleles will have both A and B antigens present on their RBCs.

The video clarifies the misconception that O blood group individuals lack antigens, when in fact they have the H antigen.

The biochemical pathways for the formation of blood group antigens are detailed, emphasizing the role of specific enzymes.

The video provides a clear understanding of the genetic basis for the different blood groups found in the human population.

The importance of the H antigen as a fundamental component of the blood group system is highlighted.

The video concludes by summarizing the key points of the blood group system's biochemistry and encourages viewer engagement.

Transcripts

Oh in the previous video we discussed

about the multiple alleles by taking the

example of leads pond within the

population now in this video we'll be

discussing about the biochemistry of

blood group system while we will be

discussing about the formation of

different antigens on the surface of

ultra sites when we talk about the blood

group of an individual is determined by

the surface proteins on it resides it is

actually what kind of antigen is present

on the surface of RBC's in human

population the system has poor

possible blood groups found within the

population it's a blood group B blood

group a B blood group and Oh blood group

in case of a blood group individuals the

a antigen is present on the surface of

RBC's in case of B blood group

individuals the B antigen is present on

the surface of RBC's in case of a B

individuals both antigens are present on

the surface of RBC's and in all

individuals the H antigen is present on

the surface of RBC's do not get confused

here that may be sometimes you might

have heard that or individuals like any

antigen on RBC's it's because the or

individuals have null alleles and do not

go for any addition of molecules on the

precursor molecule which is already

present here in the form of H antigen

and this H antigen acts as a precursor

molecule for both a and B antigens which

we are going to discuss later on in this

video now looking at the structure of

immature RBC that's devoid of any

antigen yet it has got oligosaccharide

molecule on its surface having a

structure that consists of wilcos

galactose and Estelle glucose mine and

galactose this is the basic structure of

alpha site prior to any addition of

fully functional surface antigens after

that the chromosome number 19 has got H

locus that's the H antigen locus which

consists of fut one gene at antigen gene

and this fut one gene codes for pure

Cosell transferase enzyme we see the

function of mucosal transferase enzyme

is that it will transfer the Fuko sugar

from Gd

chuckles molecule towards the

oligosaccharide chain on

RBC surface as you can see in this

diagram on this addition the surface

molecule is now called H antigen and

this H antigen molecule is precursor for

both a and B antigens now we have four

scenarios here individuals expressing a

lead individual is expressing B allele

individual is expressing Oly Oly in

homo-sex condition or individuals

expressing both a and B allele

now let's take our individuals first the

individuals were or allele in homozygous

condition this allele is null allele and

it will produce a non-functional protein

and this non-functional protein will not

add any molecule to the precursor h

antigen for the h antigen on the surface

of RBC remains as such in its form in Oh

blood group individuals that's why we

say Oh blood group individuals does not

have surface antigen but actually they

have the H antigen on its surface that's

already present prior to orally

expressing now we have individuals

expressing a allele and individuals

expressing ble the a allele codes for an

enzyme called gal neg transferase or

simply an a style glucosamine

transferase whereas the B allele codes

for the enzyme called gal transferase

the RBC has precursor molecule in the

form of H antigen only to surface as

shown in the figure and to that gal Lake

transferase catalyzed the reaction of

transfer of cowl-neck or simply a nest

alkaloid Tosa my this catalyzes the

formation of a antigen from h antigen

then we have B allele expressing

individuals while we get gal transferase

enzyme and this gal transferase enzyme

transfers their like toes towards the

edge antigen which catalyzes the

formation of B antigen from H antigen so

this is how the formation of a and B

antigen takes place from H antigen with

the transferase enzymes so this is all

about biochemistry op blood group

system I hope you liked the video if you

liked it give it a thumbs

and make sure to subscribe channel

thanks