Brock Biology of Microorganisms (15th Edition)
15th Edition
ISBN: 9780134261928
Author: Michael T. Madigan, Kelly S. Bender, Daniel H. Buckley, W. Matthew Sattley, David A. 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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Multiple mechanisms contribute to create a wide diversity in MHC protein expression between different individuals in the population. In addition to the genetic polymorphism of MHC genes, what additional mechanism(s) contribute to this diversity?
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?
The 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?
Chapter 27 Solutions
Brock Biology of Microorganisms (15th Edition)
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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- There are two classes of MHC molecules with distinct subunit compositions but similar three-dimensional structures. Both MHC class I and MHC class II molecules are highly polymorphic genes in the human population, with tens to hundreds of different alleles co-existing in the population. This means that a comparison of the MHC protein sequences between two individuals would reveal amino acid differences between one individual and the next. However, these amino acid differences are not randomly distributed along the entire protein, but are clustered in certain locations. In the figure below, the diagram that most correctly indicates the regions of greatest variability between different MHC proteins (shown by the red highlights) is:arrow_forwardExplain how dendritic cells or B cells can express six different versions of MHC1 and six to eight versions of MHC2. What is the evolutionary benefit of MHC being highly polymorphic and polygenic? thank you!arrow_forwardIn 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…arrow_forward
- Why is the concentration of this ligand for the NK-cell receptor CD94:NKG2A. on the target cell an effective measure of the presence or absence of classical MHC class I molecules?arrow_forwardSome viruses have mechanisms to down-regulate MHC class I protein expression on the surface of cells in which the virus is replicating. This immune evasion strategy might prevent effector CD8 cytotoxic T cells from recognizing and killing the virus-infected cells. Would this immune evasion strategy also prevent the initial activation of virus-specific CD8 T cells? Yes, because no viral peptide:MHC class I complexes would form to activate CD8 T cells. No, because dendritic cells would take up infected cells and cross-present viral peptides to activate CD8 T cells. No, because some presentation of MHC class I complexes with viral peptides would occur before the virus could down-regulate all the surface MHC class I protein. Yes, because this immune evasion strategy would also function in dendritic cells, even if the virus doesn’t replicate in dendritic cells. No, because the type I interferon response induced by the virus infection will up-regulate MHC class I expression and override the…arrow_forwardThree 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-2arrow_forward
- The high degree of polymorphism in MHC class I molecules that present antigens to CD8 T cells is found in _______ because _______ is/are monomorphic: a. β2-microglobulin; the heavy chain b. both the α and β chains; none c. HLA-DOβ; HLA-DOα d. the heavy chain; β2-microglobulin e. HLA-E and HLA-G; HLA-F.arrow_forwardVariable 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_forwardIn regard to antigen presentation, MHC class I molecules usually present peptides derived from _____, whereas MHC class II molecules usually present peptides derived from _____. a. intracellular cytosolic sources; vesicular system b. phagolysosome; proteasomes c. MIIC; self proteins d. CLIP; HLA-DM e. endocytic vesicles; endoplasmic reticulum.arrow_forward
- Antibody 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_forwardOn which types of cells are the two classes of major histocompatibility complex (MHC) proteins located and what type of antigen do they display? MHC I proteins are found on the surface of antigen-presenting cells and display exogenous antigens, while MHC II proteins are found on the surface of most cells, and display endogenous antigens. MHC I proteins are found inside most cells, and display exogenous antigens, while MHC II proteins are found on the surface of antigen-presenting cells and display endogenous antigens. MHC I proteins are found inside all cells and display exogenous antigens, while MHC II proteins are found inside antigen-presenting cells and display endogenous antigens. MHC I proteins are found on the surface of most cells and display endogenous antigens, while MHC II proteins are only found on antigen-presenting cells and display exogenous antigens.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_forward
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