Structure of B and T Lymphocyte Receptors Flashcards
what do B cell receptors contain?
- an antibody of defined specificity
what do T cell receptors contain?
- structure that resembles part of an antibody molecule (Fab fragement) that is specific for peptides from the antigen that was presented to the naive T lymphocyte by the APC
what is the structure of B-cell receptors?
quaternary protein with two identical heavy chains and two identical light chains
what are co-receptors and what are some examples?
BCRs cannot signal directly when they bind an antigen so to transmit activation signals into the cell they use co-receptors
- Igα and Igβ
- CD19/CD21/CD81
explain how lignand receptor binding causes molecular changes?
dimerization or multimerization occurs and the receptors are clustered and localized in lipid rafts
what are the two antibody forms?
membrane bound form and secreted Ig form
what produces antibodies?
B lymphocytes and plasma cells
what are plasma cells?
highly differentiated B lymphocytes that are specialized in the secretion of antibodies
what is the structure of the typical antibody molecule IgG?
- divalent
- two binding sites for cross linking
- proline rich hinge region that allows an extension
- 2 identical light and 2 identical heavy chains
- held together by disulfide bonds
- contains variable and constant domains
what are the two light chains and what are the five heavy chains?
- kappa and lambda
- mu, alpha, gamma, delta and epsilon
compare the amino acid sequences for the variable region and the constant region?
- variable region: the amino acid sequences of the
antibody molecules produced by different clones of B lymphocytes VARY - constant region: identical amino acid sequence even when different clones of B lymphocytes produce antibody molecules.
what is the difference between the C terminal and N terminal of a typical antibody molecules (IgG)?
- N terminal: antigen binding site/recognition site (Fab)
- C terminal: mediates effector activities (Fc, c=crystallization)
what is a paratope?
the structure of the Fab fragment of an ANTIBODY that makes direct contact with an antigen
what is an epitope?
the portion of the ANTIGEN that is bound to the antibody
how many hypervariable regions are there in the heavy and light chains of an antibody?
3 on each
the residues in the hypervariable region make?? what is another name for the hypervariable region?
- the closest contact with antigen at the antigen combing sites
- complementary determining region
what does the amino acid sequence in the complementary determining regions determine?
shape, charge and chemistry of an antibody for its antigen ie specificity
describe antigen-antibody interactions
- non-covalent bonds
- reversible
- require close steric fit
- closer fit= tighter fit= higher affinity binding specificity
what is affinity?
the strength of an individual bond for a certain interaction between antibody and antigen
what is avidity?
combined strength of binding of multiple interactions (multivalent)
for T cell receptor complexes with coreceptors what is the functions of CD3, CD4 and 8 and CD28?
- CD3 contains ITAMs that transmits signals to the cell
- CD4 and CD8 increase the avidity
- CD28 engages CD80/86 on the antigen presenting cell to activate the T cell
what are the 5 immunoglobulins?
- IgG
- IgA
- IgM
- IgD
- IgE
what is the heavy chain and light chain composition of secreted IgG?
heavy chain: gamma
light chain: kappa or lambda
what are some specific properties of secreted IgG?
- monomer
- crosses the placenta (protects fetus only in womb)
- found in the blood stream and tissue fluid
