CH 5 immuno

Ch. 5 1. a) Vk gene segments sometimes join to Clamba gene segments. FALSE- Vk gene segments and C1 are located on separate chromosomes and cannot be brought together during gene rearrangement. b) With the exception of a switch to IgD, immunoglobulin class switching is mediated by DNA rearrangements. TRUE c) Separate exons encode the transmembrane portion of each membrane immunoglobulin. TRUE d) Although each B cell carries two alleles encoding the immunoglobulin heavy and light chains, only one allele is expressed. TRUE e) Primary transcripts are processed into functional mRNA by removal of introns, capping, and addition of a poly-A tail. TRUE f) The primary transcript is an RNA complement of the coding strand of the DNA and includes both introns and exons. TRUE 3. Considering only combinatorial joining of gene segments and association of light and heavy chains, how many different antibody molecules potentially could be generated from germ-line DNA containing 500 VL and 4 JL gene segments and 300 VH, 15 DH, and 4 JH gene segments? Light Chains: 500 x VL 3 4 JL = 2 3 10^3 Heavy Chains: 300 VH x 3 15 DH x 3 4 JH= 1.83 x10^4 Antibody molecules: (2 x 3 10^3 LCs) x 3(1.8 x 3 10^4 HCs) = 3.6 x 3 10^7 4. a) Recombination of immunoglobulin gene segments serves to: - promote Ig diversification - assemble a complete Ig coding sequence - allow changes in coding information during B-cell maturation b) Somatic mutation of immunoglobulin genes accounts for: - affinity maturation c) The frequency of somatic mutation in Ig genes is greatest during: - generation of memory B cells d) Kappa and lambda light-chain genes: - none…. Eff. e) Generation of combinatorial diversity among immunoglobulins involves: - DNA rearrangement - recombination signal sequences - one-turn/ two-turn joining rule f) A B cell becomes immunocompetent: - following productive rearrangement of variable-region heavy-chain and light-chain gene segments in germ-line DNA g) The mechanism that permits immunoglobulins to be synthesized in either a membrane-bound or secreted form is: - differential RNA processing 6. You have been given a cloned myeloma cell line that secrets IgG with the molecular formula y2lamba2 . Both the….. 7. You have a B-cell lymphoma that has made nonproductive rearrangements for both heavy-chain alleles. What is the arrangement of its light-chain DNA? Why? The k-chain DNA must have the germ-line configuration because a productive heavy-chain rearrangement must occur before the light-chain (k) DNA can begin to rearrange. 8. Indicate whether each of the class switches indicated below can occur or cannot occur: a) IgM to IgD NO b) IgM to IgA YES c) IgE to IgG NO d) IgA to IgG NO e) IgM to IgG YES 12. a) RAG-1 and RAG-2 -Enzymes expressed in developing B cells b) Double-strand break repair (DSBR) enzymes - Enzymes expressed in developing B cells - Enzymes expressed in mature B cells - Enzymes that are defective in SCID mice c) Coding joints - Junctions between immunoglobulin gene segments formed during rearrangement d) RSSs - Conserved DNA sequences, located adjacent to V,D, and J segments, that help direct gene rearrangement e) P-nucleotides - Source of diversity in antibody heavy chains - Product of endonuclease cleavage of hairpin intermediates in Ig-gene rearrangement f) N-nucleotides - Source of diversity in antibody heavy chains - Nucleotides added by TdT enzyme g) Promoters - DNA regulatory sequences - Nucleotide sequences located close to each leader segment in immunoglobulin genes to which RNA polymerase binds f) Enhancers - DNA regulatory sequences - Nucleotide sequences that greatly increase the rate of transcription of rearranged immunoglobulin genes compared with germ-line DNA 13. Because mouse antibodies are rapidly cleared from the human system, therapeutic anti0idiotype antibodies derived from mice are most effective if they are humanized; i.e., genetic engineering is used to replace all mouse sequences except the CERs with human Ig sequences. It is highly unlikely that the B-cell lymphomas of different patients will have the same idiotype. Therefore, this is an approach that would have to be repeated for every B-lymphoma patient to whom it was applied.