T-Cell biochemistry Flashcards
Downsides of antibodies:
There are things that antibodies cannot be used to combat effectively, what are these things?
- Intracellular pathogens
- Bacteria and Viruses
- Tumours
Downsides of antibodies:
As antibodies cannot be used to combat everything, what else does the immune system need?
The T-cell
The T-cell receptor (TCR):
Approximately how many T-Cell receptors are on the surface of the the T-Cell?
10^5
The T-cell receptor (TCR):
What does the TCR consist of?
- 2 polypeptide chains
- Majority - ⍺β T-cells
- Minority - 𝛾δ T-cells
Differences between the TCR and Fab:
C⍺:
Half of the domain, what does that closest to the β chain form?
- Forms a β-sheet
Differences between the TCR and Fab:
C⍺:
What is the other half made up of?
- The other half is made up of loosely packed strand and a short stretch of ⍺-helix
- Held to one of the strands of the β-domain to this helix
Differences between the TCR and Fab:
What are the interactions between C⍺ and Cβ assisted by?
- Carbohydrates
- Carbohydrate on C⍺ forming hydrogen bonds with the amino acids of Cβ.
Differences between the TCR and Fab:
CDR loops: what are they fairly similar to?
Fairly similar between an antibody and the TCR, some displacement
Differences between the TCR and Fab:
What do TCRs have a 4th of? and where is it found?
- TCRs have a 4th hypervariable region
- Away from the antibody binding site
T-cell receptor gene rearrangement:
TCR⍺ is similar to what chain? and why?
- The Immunoglobulin light chain
- V and J segments
T-cell receptor gene rearrangement:
TCRβ is similar to what chain? and why?
- The immunoglobulin heavy chain
- V, D, and J segments
T-cell receptor gene rearrangement:
When do the genes rearrange and where does the process happen?
What is this process similar to?
- The genes rearrange during T-cell development
- In the thymus
- In a process similar to the Germinal Centre Reaction for B-cells
T-cell Receptors don’t bind antigen directly:
Where do antibodies bind antigen?
- Antibodies bind antigen in the circulation
- Whether that be free flowing or on the surface of the pathogen
T-cell Receptors don’t bind antigen directly:
What do T cells bind to?
- T-cell bind to an antigen-protein complex
MHC-I and MHC-II:
What is MHC?
MHC= Major histocompatibility complex
T-cell Receptors don’t bind antigen directly:
What is an antigen-protein complex?
- Short, continuous amino acid sequences from an unfolded protein
-Presented as part of a protein complex on the surface of an antigen presenting cell
MHC-I and MHC-II:
The 2 are closely related in overall structure and function, but what do they differ in?
- Differ in their protein subunits
- 2 paired domains nearest the membrane resemble an immunoglobulin
- 2 domains furthest from the membrane produce a peptide-binding cleft
MHC-I and MHC-II:
What does MHC-I consist of?
- 2 Polypeptide chains
- The ⍺-chain, which makes up 3 domains of the protein and crosses the membrane and forms the entire peptide binding cleft
- Β2-microglobulin associates with the ⍺3 domain
MHC-I and MHC-II:
What does MHC-II consist of?
- 2 polypeptide chains
- Both the ⍺ and the β chain cross the membrane
- The peptide binding cleft is made up of both the ⍺ and the β chain
MHC-I and MHC-II:
What do MHCs need to be able to do in order to stimulate T-Cells?
- MHCs need to be able to bind a large variety of peptides
MHC-I and MHC-II:
When are MHC proteins unstable?
- MHC proteins are unstable when not bound to a peptide
MHC-I and MHC-II:
What length of amino acids to MHC-I and MHC-II bind peptides to?
- MHC-I binds peptides 8-10 amino acids in length
- MHC-II can bind peptides of any length
MHC-I and MHC-II:
MHC-I binds and presents intracellular peptides that reside where?
- In the cytosol
MHC-I and MHC-II:
Where do some pathogenic bacteria and some protozoa reside?
- Reside inside vacuoles once inside the cell and peptides are presented on MHC-II
