Block A - lecture 2 Flashcards
what is the part of the T cell that recognises the antigen ?
the T cell receptor
what chains make up the TCR ?
an alpha and a beta chain
are the chains always constant or variable and explain
There is a variable beta and a variable alpha chain. The constant regions do not change in sequence from T cell to cell and they are located closer to the membrane
how do the variable regions form ?
The variable regions are deliberately mutated to generate variants so that it could fit a range of antigen and peptides
are the variable regions in T cells all the same or different ?
the variable regions in an individual of T cell are all the same , however each T cell generates its own particular variable region. So that you have a series of different T cells. Within each T cell there are thousands of receptors and they are all the same
what do the TCR share similarities with ?
the immunoglobin domains
what is the MHC class II molecule on and what does it present to ?
on the presenting cell , not the T cell. It contains the peptide and presents it to the T cell
where does the TCR lie and what does it contain that recognises the peptide from the APC?
Within the bilayer, the T cell receptor lies and it contains the alpha and beta chains and this is what recognises the peptide from the APC. The peptide will be complimentary in shape to the receptor.
how come the T cell doesn’t contain a signalling capacity and as a result what causes the signalling ability ?
It does not contain tails that extend into the cytosol and it doesn’t have a signalling capability as a result of this. The T cell receptor and accessory proteins that are involved in signalling surround the receptor and collectively called the T cell receptor complex.
explain the CD3 complex ?
A major part of the complex that is closest to the binding site is called the CD3 complex chains and they lie to the right. They consist of 4 peptide chains that are labelled as Epsilon, delta and gamma, there are 3 different types of chains. The epsilon chain surrounds the delta and gamma chains to form a tetrameric complex. This CD3 complex interacts with 2 further chains called zeta chains that are free within the membrane of the inactivated T cell.
explain the CD4 marker proteins ?
In addition to the zeta chains, there is CD4 marker proteins to the left which contains the receptor binding site for the MHC molecule. So that when the APC, containing the MHC class II arrives, the peptide binds to the T cell receptor and the CD4 proteins bind to the MHC class II.
explain the location of the LCK molecule and it’s function ?
It is attached to CD4 but not covalently is a protein called LCK, it is a kinase (add phosphates) and found on the inner bilayer of the cell.
CD45 ?
CD45 is found in the membrane and it is an enzyme, a phosphatase (removes phosphates).
ITAMS?
ITAMS (immunoreceptor Tyrosine Activation Motifs) these are motifs or patterns that are commonly recurring in a variety of proteins when it comes to signalling. They are common in immune cells. The motifs are the recurring pattern and the amino acid is what is recurring. This is important as tyrosine signalling is occurring and it is the phosphorylation of tyrosine using a kinase ( adding a phosphate) or phosphatase ( removing a phosphate) that affects signalling.
in the ITAMS , what is the Y and L showing ?
Y is the code name for tyrosine, and this is separated by 2 amino acids and then leucine ( L). Then between 6 to 8 intervening amino acids then repeated of the tyrosine and 2 amino acids separated them from leucine.
