lecture 4 - blood: blood groups Flashcards
what are blood groups?
a classification of blood based on the presence (or absence) of inherited antigenic substances on the surface of RBCs
what is an antigen?
a molecule that induces an immune response
those on RBCs will mount are red blood cell surface antigens
how many blood group systems are there?
30
how do we get our blood groups?
they are inherited and represent contributions from both parents
an individual always almost has the same blood group for life but it may change due to infection, malignancy, autoimmune disease or after a bone marrow transplant
what is the ABO system
determined by the terminal sugar structure in the surface of RBCs
what are the major sugars in the ABO system?
fucose galactose N-acetylgalactosamine N-acetylglucosamine sialic acid
what genes control the ABO system?
genes ABO and H
what do the ABO and H genes encode?
glycotransferases
• enzymes that transfer monosaccharides to polysaccharide chains
what are the alleles of the ABO gene?
A, B and O
A and B are dominant to O
O allele codes a truncated, non-functional proteins
what are the alleles of the H gene?
H and h
what does the H allele code for?
fucosyl transferase (FUT1) which converts precursor substance on RBCs to H antigen
H substance is required for A and B antigen production
adds a fucose to the terminal galactose
what does the h allele code for?
a non-functional protein
what substances do HH, Hh and hh individuals make?
HH make H substance
Hh make H substance
hh dont make H substance
hh individuals
dont possess a functioning copy of the FUT1 gene
bombay phenotype
no ill effect but people with this blood group can only have transfusions from others with the same blood group
may have functional A or B genes but as they don’t have a functional FUT1 they cannot make substance H so can’t make ABO antigens
where is the ABO gene located?
chromosome 9
the A and B alleles differ by 7 nucleotide substitutions