IMM2011 Lecture Notes - Lecture 6: B-Cell Receptor, Complementarity-Determining Region, Pattern Recognition Receptor

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Online lesson 1: T and b cell development:
An antigen : molecule that will bind to an antigen receptor; these are the T cell antigen
receptor (TCR) and the B cell antigen receptor (BCR)
Types of antigens that bind to B cell receptor:
-protein, carbohydrate, lipids, or nucleic aid.
Antigen receptor
- Hypervariable region or complementarity determining region:
T cell receptors:
- More restericted than b cell receptors.
- Mainly bind to protein peptides (short string of amino acid).
- Only those presented to them by MHC molecules
- This binding is different to pattern recognition receptors binding PAMPS.
- T and b cell receptors unlike pattern recognition which are quite limited . they are
unlimited in number .
- Each t and b cell have different receptors. Which responds to any pathogen that the
body comes into contact with.
- Immune system can make more t cell receptors than genes.
B cell:
- Produce and secrete antibodies
- B cell receptor is an antibody molecule that is embedded on the surface of b cell
- B cell activated”= secrete antibody,also called immunoglobulin (ig).
- Each b cell will express thousand of b cell receptors on their surface and these have
the same specificity.
- Individual b cell expressed different b cell receptors that bind to unique antigen
specificity.
Antibody:secreted form of b cell receptor and they bind to antigen.
- It is y shaped structure.
- Contains two binding sites which have the same
structure.
- 4 polypeptide chains: 2 identical heavy chains and 2
identical light chains.
-Red region: variable region where antibodies bind to
antigen which means there differences amino acid
composition between antibodies, gives antibody specificity
-Blue: constant region which is same in all antibodies,
high similarity in amino acid across with different antibody
molecules.
- Heavy + light chain have region called immunoglobulin
domains.
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C= constant region, H= heavy chain, V= variable region and L= light chain
CH1:this s the first constant domain in the heavy chain.
CH2: this is the second constant demain in the heavy chain
CH3: third constant domain in heavy chain
VH: variable in the heavy chain
Cl: this is the constant in the light chain.
VL: variable domain in the light chian.
Hinge region: provide flexibility at these points, allowing the arms to
move.
Antibodies with hinge regions are not fixed in how far apart their
binding sites need to be.
Disulfide bond: between the heavy chain and the heavy and light
chain. Associated with covalent bonds which bind the chain together
and provide structural support.
Antibodies bind epitopes:
Epitopes: small and specific region of the antigen that is bound by the antibody.
For t cell: the epitopes is the specific piece of peptide that is being displayed by the MHC.
Conformation epitopes:
- In which the epitope is more complex
- Might be where distant loops of a protein are found close together.
Linear epitopes: such as string of amino acids as part of a protein.
Antibody binding:
- Antibodies bind to target antigen at the antigen binding site.
- Pocket:generated by heavy and light chains.
- Antibody binds to the shape of epitope/
- Antibody needs to see or bind the antigen(from a pathogen) as it exists in nature.
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Document Summary

Online lesson 1: t and b cell development: An antigen : molecule that will bind to an antigen receptor ; these are the t cell antigen receptor (tcr) and the b cell antigen receptor (bcr ) Types of antigens that bind to b cell receptor: Mainly bind to protein peptides (short string of amino acid). Only those presented to them by mhc molecules. This binding is different to pattern recognition receptors binding pamps. T and b cell receptors unlike pattern recognition which are quite limited . they are unlimited in number . Each t and b cell have different receptors. Which responds to any pathogen that the body comes into contact with. Immune system can make more t cell receptors than genes. B cell receptor is an antibody molecule that is embedded on the surface of b cell. B cell activated = secrete antibody,also called immunoglobulin (ig).

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