What chromosomes in humans are the kappa and gamma light chains on?
kappa - 2
In humans what chromosome is the heavy chain on?
What segments are the light chains encoded by in the genome?
V (variable) and J(junctional) gene segments
What segments are the heavy chains encoded by in the genome?
V (variable), J (junctional) and D (diversity)
What is combination diversity?
Generating variable region exons by recombining gene segments
In heavy chain gene recombination which two segments join first.
followed by addition of V to make VDJ
How many nucleotides are in the recombination signal sequences?
7 or 9 nucleotides that flak the gene segments
How many nucleotides separate the flanking nucleotides around gene segments?
12 or 23
the 12 23 rule
What does the RAG complex contain?
RAG1 and RAG2 and other enzymes
Is the RAG complex expressed in
a) T cells
b) B cells
What is junctional diversity? and what causes it?
- Diversity in the junction between gene segments (DS cut is precise, the re joining is not)
- caused by RAG complex
What adds palindromic nucleotides (p-nucleotides) to blunt end of DNA post hair pin loop cleavage in junctional diversity?
The RAG complex
What adds N-nucleotides?
Tdt (terminal deoxynucleotidyl transferase).
These add 1, 2 or 3 nt to either strand
What happen if the recombination of gene segments s unsuccessful in making productive protein?
B Cell dies
What does somatic hypermutation do?
Increases diversity at CDR regions.
What enzyme drives somatic hypermutation?
AID (activation induced cytidine deaminase)
This enzyme is only made proliferating B cells
What does AID do?
Converts cytosine to uracil which is then converted to other bases
The process of somatic hypermutation drives an event called…?
What is affinity maturation?
An improvement of binding strength of antibody over time.
How does somatic hyper mutation lead to affinity maturation?
- variability generated on variable regions
- antibody on b cells with tightest affinity binds antigen
- this b cell population expands
Following rearrangements you get initial transcription which includes which constant gene segments?
mu and delta
(these are the first immunoglobulins to be expressed)
These regions are then processed to give either IgM or IgD
Unactivated B cells in the periphery will coexpress which immunoglobulins?
IgM and IgD
They are expressed on the B cells and act as receptors. These have the same VDJ and hence same specificity
Between IgM and IgD which exists in the serum?
IgM, following differentiation of B cell into plasma cell IgD is not expressed
What generates the difference between membrane bound or secreted IgM?
There are two exons:
Mc (membrane coding)- M1 and M2
Sc (secretion coding)
Is the secreted or the membrane form of IgM pentameric?
membrane bound is monomeric
Which terminus of the heavy chain determines whether the IgM is membrane bound or secreted?
The c terminus. As this is what determines whether the protein is anchored in the membrane or trafficked to ER to form a pentamer prior to secretion.
How many amino acids of the C terminus of IgM are identical regardless of whether it is secreted or membrane bound?
After this amino acids are more hydrophillic or hydrophobic depending on whether they are secreted or membrane bound
In the membrane bound form of IgM are there negative amino acids on the cytoplasmic end or on the outside?
Negative aa are on the outside and pisotive charges on cytoplasmic.
What is class switching?
Changing the class of immunoglobulin that the cell expresses.
What is the first immunoglobulin to be produced post production of IgM?
remember IgD is not expressed in activated B cells
What dictates which antibody classes are made following stimulation?
Cytokines dictate which antibody classes are made
What catlyses the class switching?