EBK BROCK BIOLOGY OF MICROORGANISMS
15th Edition
ISBN: 8220103633352
Author: Stahl
Publisher: PEARSON
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Chapter 27.6, Problem 1CR
Q Polymorphism implies that each different MHC protein binds a different peptide motif. For the MHC class I polymorphisms, how many different MHC proteins are expressed in an individual? How many by the entire human population?
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Polymorphism implies that each different MHCprotein binds a different peptide motif. For the MHCclass I polymorphisms, how many different MHCproteins are expressed in an individual? How many bythe entire human population?
In the 1980s, a mutant strain of mice was identified, carrying amino acid changes in the MHC class II gene. This mutant strain was derived from C57Bl/6 mice, which carry the H-2b haplotype. Inbred H-2b mice express only one MHC class II protein, called Ab. The mutant strain, called ‘bm12’ was found to have 3 amino acid changes in the Ab protein, at positions 67, 70, and 71 of the Aβ chain. The positions of these amino acid changes on the MHC class II structure are shown below by the red circles in Figure Q6.30A. On the right, the side view diagram of MHC class II shows the direction of these three amino acid side chains.
Initial experiments with wild-type C57Bl/6 mice and bm12 mice showed that the wild-type mice made a robust CD4 T cell response after immunization with the insulin protein isolated from a cow; in contrast, the bm12 mice failed to make any detectable response to this foreign protein. Epitope mapping studies identified amino acid residues 1–14 of the bovine insulin A…
Three major cell types, dendritic cells, macrophages, and B cells, present peptides bound to MHC class II molecules for recognition by CD4 T cells. In general, these peptides are derived from proteins or pathogens taken up by the cell by endocytosis, phagocytosis, or macropinocytosis. Based on these pathways of antigen uptake, some of the enzymes that degrade proteins to generate peptides for MHC class II presentation are:
Ubiquitin ligases that tag proteins for degradation by the proteasome
ATP transporter proteins that deliver endocytic proteins into the cytosol for degradation
Cysteine proteases like cathepsins that function at acidic pH
The lysosomal thiol reductase found in the endosomes
The lysosome-associated membrane trafficking protein, LAMP-2
Chapter 27 Solutions
EBK BROCK BIOLOGY OF MICROORGANISMS
Ch. 27.1 - Prob. 1MQCh. 27.1 - Prob. 2MQCh. 27.1 - Distinguish between clonal deletion and clonal...Ch. 27.1 - QWhy is it necessary that all three defining...Ch. 27.2 - Identify the intrinsic and extrinsic properties of...Ch. 27.2 - Describe an epitope recognized by an antibody, and...Ch. 27.2 - Give an example for each: natural and artificial...Ch. 27.2 - QWhat properties are required for a vaccine to...Ch. 27.3 - Summarize antibody production starting with...Ch. 27.3 - Differentiate among antibody classes using...
Ch. 27.3 - Prob. 3MQCh. 27.3 - QDescribe the structural and functional...Ch. 27.4 - Draw a complete Ig molecule and identify...Ch. 27.4 - Describe antigen binding to the CDR1, 2, and 3...Ch. 27.4 - Describe the recombination events that produce a...Ch. 27.4 - QWhich Ig chains are used to construct a complete...Ch. 27.5 - Identify the cells that display MHC class I and...Ch. 27.5 - Compare the MHC I and MHC II protein structures...Ch. 27.5 - Define the sequence of events for processing and...Ch. 27.5 - QDescribe the basic structure of class I and class...Ch. 27.6 - Define polymorphism and polygeny as they apply to...Ch. 27.6 - How does a single MHC protein present many...Ch. 27.6 - QPolymorphism implies that each different MHC...Ch. 27.7 - Prob. 1MQCh. 27.7 - Identify diversity-generating mechanisms unique to...Ch. 27.7 - Describe and compare the structural features of Ig...Ch. 27.7 - QWhat diversity-generating mechanisms function to...Ch. 27.8 - Describe the mechanism used by Tc cells to...Ch. 27.8 - Describe the effector system (the cell-killing...Ch. 27.8 - Compare and contrast the roles and activities of...Ch. 27.8 - QWhat mechanism do Tc cells use to identify and...Ch. 27.9 - Discriminate between immediate hypersensitivity...Ch. 27.9 - Provide examples and mechanisms for an...Ch. 27.9 - QHow do immediate and delayed-type...Ch. 27.10 - Describe the binding site for superantigens on T...Ch. 27.10 - Compare and contrast the immunodeficiency observed...Ch. 27.10 - Prob. 3MQCh. 27.10 - Prob. 1CRCh. 27 - Antibodies of the IgA class are probably more...Ch. 27 - Prob. 2AQCh. 27 - Polymorphism implies that each different MHC...Ch. 27 - What problems would arise if a person had a...
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- A cell line carrying a mutation in a single gene is found to express very low levels of MHC class I on its surface. When infected with influenza virus, these cells are not recognized nor are they killed by a CD8 T cell line specific for an influenza peptide bound to the MHC class I protein expressed by these cells. Incubation of the mutant cell line with a large excess of this peptide in the cell culture medium overnight leads to the results shown below. What is the most likely candidate for the gene that is defective in the mutant cell line?arrow_forwardFor immunoglobulin heavy and light chain genes, and for T-cell receptor b chain genes, there are a large number of V gene segments, and relatively few J and/or D segments that rearrange to form the final coding sequence for each gene. The TCR a locus is different in this regard, and this difference is thought to reflect the fact that nearly all a:b T-cell receptors recognize a peptide bound to an MHC molecule. This unique feature of the T-cell receptor a locus is: The presence of only five different Va gene segments The presence of two different Ca coding sequences The presence of over sixty different Ja gene segments The absence of D gene segments The large sequence distance separating the Va gene segments from the Ja gene segmentsarrow_forwardThe expression of MHC class II molecules is restricted to a small number of cell types. A. What are these cell types? B. Which of these cell types populate the thymus or circulate through it, and what role do they play in mediating positive and/or negative selection? C. Can you explain why it would be detrimental for noncirculating cells that populate tissues and glands to express MHC class II molecules?arrow_forward
- MHC polymorphism at individual MHC genes appears to have been strongly selected by evolutionary pressures. In other words, there appears to be selection for maintaining hundreds to thousands of different alleles of each MHC gene in the population. This notion is based on the observation that nucleotide differences between alleles that lead to amino acid substitutions are more frequent than those that are silent substitutions (i.e., not changing the amino acid sequence of the protein). In addition, the positions within the MHC protein where most of the allelic sequence variation occurs are not randomly distributed, but are concentrated in certain regions of the MHC protein. This latter point indicates: That some nucleotide sequences within the MHC genes are hot-spots for mutation That MHC genes are more susceptible to point mutations than to larger nucleotide deletions That MHC allelic polymorphism has been driven by selection for diversity in peptide binding specificity That MHC genes…arrow_forwardMost of the enzymes involved in immunoglobulin gene rearrangement are ubiquitously expressed in all cells of the body. However, the specific recombination events between V, J, and D gene segments that generate antibody diversity occur only in developing B cells. How do RAG-1 and RAG-2 ensure that recombination takes place at antibody gene segments?arrow_forwardAntibody diversity is generated by multiple mechanisms, each of which contributes to the generation of antibodies with up to 1011 different amino acid sequences in their antigen-binding sites. Several of these mechanisms involve changes in the DNA sequences encoding the antibody heavy and light chain proteins. One mechanism that does not rely on changes to the DNA within the immunoglobulin heavy and light chain gene loci is, instead, dependent on: The contributions of amino acids from both the heavy chain and the light chain to form the antigen-binding site The random usage of V, D, and J gene segments to form the heavy chain V region sequence The random usage of k light chains versus l light chains to pair with the heavy chain The activity of TdT to add random nucleotides at the junctions between the V, J, and D region sequences The fact that heavy chain V regions contain an extra gene segment encoded by the D region compared to light chain V regionsarrow_forward
- Variable addition and subtraction of nucleotides at the junctions between gene segments contributes to the diversity of [Qi] the third hypervariable region. The addition and subtraction of nucleotides at the junctions between V, D, and J gene segments creates antibody proteins with wide variations in the numbers of amino acids in their CDR3 regions. This variability in CDR3 length is important as: Overall variability in CDR3 sequence is needed to create a sufficiently diverse antibody repertoire. The CDR3 region is more important in binding antigen than the CDR1 and CDR2 regions are. Some light chains bind better to heavy chains with longer CDR3 region sequences. Longer CDR3 sequences generally create antibodies with higher affinity for the antigen. Some antibodies bind relatively flat surfaces and others bind deep clefts in the antigen.arrow_forwardAtaxia-telangiectasis (ATM) is a rare genetic neurodegenerative disease. About 20% of people with ATM develop acute lymphocytic leukemia or lymphoma, cancers of the immune-system cells. Cells in many of these cancers exhibit chromosome rearrangements, with chromosome breaks occurring at antibody and T-cell-receptor genes (A. L. Bredemeyer et al. 2006. Nature 442:466–470). Many people with ATM also have a weakened immune system, which makes them susceptible to respiratory infections. Research has shown that the locus that causes ATM has a role in the repair of double-strand breaks. Explain why people who have a genetic defect in the repair of doublestrand breaks might have a high incidence of chromosome rearrangements in their immune-system cells and why their immune systems might be weakened.arrow_forwardOne strategy for vaccine development currently under investigation is the use of pathogen-derived T cell epitopes as a component of the vaccine. For viral pathogens, implementing this strategy involves scanning the predicted amino acid sequences of the viral proteins for likely peptide epitopes that would bind to MHC class I and MHC class II molecules. In addition to the complication of MHC sequence polymorphism in the human population, another complication of this strategy for peptide epitopes that would bind to MHC class II proteins is: The importance of viral proteins containing peptides that are cleaved into 8–10 amino acid long fragments. The ability of viruses to mutate their proteins to avoid MHC anchor residue sequences. The fact that long peptides (>13 amino acids) are rapidly degraded in cells. The fact that MHC class II proteins are intrinsically stable, even in the absence of binding to a peptide. The absence of defined sequence motifs that predict peptide binding to…arrow_forward
- The diagram in the first figure shows simplified versions of the immunoglobulin heavy chain locus, the T-cell receptor b chain locus, and the locus encoding the RAG-1 and RAG-2 recombinases. For the sake of this question, imagine that these diagrams represent all of the gene segments present in the immunoglobulin heavy chain and T-cell receptor b chain locus. You now analyze five individuals, each of which has a single inactivating mutation in a region of one of these three loci. These mutations are each indicated by a red ‘X’ in the second figure, and are numbered 1–5. For each of these inactivating mutations, indicate the alterations and/or defects that would be seen in the repertoire of antigen receptors found in mature B and T cells in that individual. Also, for each mutation, indicate whether the individual would likely show any immunodeficiency, such as a history of recurrent infections.arrow_forwardEach immunoglobulin (Ig) domain is composed of a structure known as a ‘b-sandwich,’ which consists of two b sheets covalently linked by a disulfide bond. Only a subset of the ~110 amino acids in each domain are required to establish this overall structure, and it is these amino acids that are highly conserved when comparing Ig domains to each other. What might be the advantage of this structure for use as antibody variable domains?arrow_forwardalpha:beta TCRs are membrane-bound proteins comprised of two polypeptides linked by a disulfide bond. Both polypeptide components of the alpha:beta TCR are members of the immunoglobulin superfamily, and each of their domains share structural similarity with regions of antibody proteins. However, due to the different functions of TCRs versus antibodies, the overall domain organization of the TCR is not the same as for an antibody. In the figure below, describe three features that are incorrect illustrations of the alpha:beta TCR.arrow_forward
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