Lecture 3 Flashcards
What carries out the adaptive immune system?
B and T lymphocytes
Describe the structure of antibody (BCR)?
- 2 identical heavy chains (50 kDa)
- 2 identical light chains (25 kDa)
- bivalent
- heavy and light chains held together by interchain disulfide bonds
- secreted and membrane bound forms
What is the hinge region?
-allows antibody to bind with both arms to many different arrangements of antigens on the surfaces of pathogens
Describe th eFab fragment?
fragment antigen binding; 2 identical fragments that bind antigen
What is the Fc fragment?
fragment crystallizable; 1 fragment responsible for destroying or clearing antigen from our bodies (effector function)
What bond forms intrachain immunoglobulin domains?
disulfide bonds
Are all antibodies proteins with constant region?
no, they have variable and constant regions
what forms the antigen binding site?
variable heavy and constant light region
What is an epitope?
the region of the protein or bacteria that binds to the antibody
Difference between monoclonal and polyclonal epitope?
monoclonal- antibody that only binds to one epitope
polyclonal- antibody that can bind to many sites
What does bivalent mean?
two binding sites on binding site
What is an antigenic determinant?
region that antibody contacts
What is the difference between continuous and conformational epitopes?
continuous binds linearly and it is between amino acids
conformational- binds at different parts of the protein; usually occurs in tertiary structures that are denaturing
What are possible bonds between antigen and antibody?
noncovalent
- hydrogen
- van der waal
- electrostatic interaction
- hydrophobic forces
What is avidity?
The sum of affinity present
Wht is affinity?
the strength of binding
What is cross reactivity?
The ability for an antibody to bid to multiple epitopes
What is somatic recombination?
allows for increase diversity of antibodies
What are the kappa and lambda components of an antibody?
aprt of the light chain
- have no functional difference
- each antibody contains both of them
What makes up each domain in antibody?
2 beta sheets connected by polypeptide loops
Why is CDR3 so important in gene diversity?
It is where all the VDJ segments join forms a lot of gene diversity
What segment is in the heavy chain but not in the light chain?
Segment
D
What is different between Chain rearrangement in the Heavy and the light?
Light chain uses only V and J segments
rearragnes DNA/ DNA is loss….trasncription… RNA splicing
Heavy uses V D and J segments
- ) DJ segements join
- )V-DJ joining
- ) transcription
- ) alternative mRNA splicing that forms two products (mu and delta)
- ) translation
What are recombination signal sequences? (RSSs)
recombination signal sequence that flank each V/d/J gene segment
12/23 rule
What is the RAG complex?
recombinase composed 2 RAG1 and 2 RAG2 proteins, has endonuclease activity
What is Junctional Diversity?
random incorporation of nucleotides at coding joints
What are P nucelotides?
‘Palandromic”- consequence of RAG endonuclease action which create DNA hairpins. When repaired , the nick that opens the hairpin cna occur at several positions-> P nucelotides
What are N nucleotides?
“non template’ consequence of termina ldeoxynucleotidyl transferase (TdT). This enzyme adds nucelotides to the opened hairpin ends
What are diversifications of antibodies after B cells encounter antigen?
- secreted antibodies
- somatic hypermutation/ affinity maturation
- class switching: mechanism and significance
What class of antibodies are found on the membrane of B cell surface?
IgM and IgD
What allows plasma cells to to produce secreted antibody?
alternative RNA processing
What stabilizes the receptor of the membrane for the transmembrane antibody?
the hydrophobic region which is changed into a hydrophilic region to allow for secretion
What are somatic hypermutations?
Targeted introduction of point mutations into V regions of H and L chains
- leads to increased antibody affintiy
- carried out by Activation Cytidine Deaminase (AID) and and deaminates C–> U
What is affinity maturation?
selection of antibodies that have increased affinity for antigen
What is isotype switching (1)?
- prodcues immunoglobulin with a different constant region by identical antigen specificity
- antibodies with different constant regions have different effector functions
- homologous DNA recombination
What is isotype switchign (2)?
DNA is lost
-further switching to downstream isotypes can take plae subsequently
What is IgM?
- monomer on B-cell
- pentamer in serum
- activates complement
- neutralization (inactivation of (pathgen/toxin) - has 10 binding sites
What is IgA?
- 2 subclasses
- IgA1- monomer in serum
- IgA2-dimer in secretions
functions
- neitralization
- opsonization
- major form of immunity at mucosal surface
- More IgA made than any other antibidy
What is IgG?
4 subclasses
longest 1/2 life —> passive immunization
Functions neutralization opsonization complement activation **Cross placenta
What are IgD and IgE?
IgD- monomer
- B cell receptor
- binds to basophils
IgE-monomer
- least abundant in serum–> binds to mast cells and basophils via Fc region
- immunity against parasitic infections
- mediates allergic reactions
