Biology: The Unity and Diversity of Life (MindTap Course List)
14th Edition
ISBN: 9781305073951
Author: Cecie Starr, Ralph Taggart, Christine Evers, Lisa Starr
Publisher: Cengage Learning
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Chapter 20, Problem 4DAA
Adapting to Host Defenses Surface proteins called HLAs allow white blood cells to detect HIV particles and fight an infection. In a recent study, scientists tested whether HIV is adapting to this host defense. They did so by looking at the frequency of a specific mutation (1135X) in HIV. This “escape mutation” helps the virus avoid detection by a version of the HLA protein (HLA-B*51) that is common in some regions of the world, but not in others. FIGURE 20.19 shows the percentage of HIV-positive people who had HIV with the 1135X mutation. Data were collected at medical centers from several parts of the world.
FIGURE 20.19 Regional variation in the frequency of the 1135X escape mutation among HIV-positive people. For each region, pink bars represent the percentage of people whose blood cells have HLA-B*51. and thus cannot detect 1135X mutants. Blue bars represent the percentage of people with other versions of the HLA protein. These people have blood cells that can detect and fight HIV even if it has the 1135X mutation.
4. Japan has a high frequency of HLA-B*51; about half the population has it. How might this explain the high frequency of the 1135X mutation in Japanese with other HLAs?
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Which of the following is false when considering the CCR5Δ32 mutation?
a) The mutation prevents the entry of HIV-1 into a T cell.
b) The deletion that produced CCR5Δ32 caused a frameshift which extends the length of the protein product.
c) CCR5Δ32 prevents infection by HIV-1 in homozygotes but only delays the onset of HIV symptoms in heterozygotes.
d) The protein product produced by CCR5Δ32 is altered in such a manner that it cannot embed in the cell membrane.
One 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…
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 regions
Chapter 20 Solutions
Biology: The Unity and Diversity of Life (MindTap Course List)
Ch. 20 - Prob. 1SQCh. 20 - Prob. 2SQCh. 20 - Prob. 3SQCh. 20 - Prob. 4SQCh. 20 - __________ do not reproduce sexually. a....Ch. 20 - Prob. 6SQCh. 20 - Adapting to Host Defenses Surface proteins called...Ch. 20 - Prob. 2DAACh. 20 - Prob. 3DAACh. 20 - Adapting to Host Defenses Surface proteins called...
Ch. 20 - Prob. 7SQCh. 20 - Bacteria that serve as decomposers are ___ . a....Ch. 20 - Prob. 9SQCh. 20 - Formation of a(n) ___ allows some soil bacteria to...Ch. 20 - Prob. 11SQCh. 20 - Prob. 12SQCh. 20 - Which of these diseases is caused by bacteria? a....Ch. 20 - Prob. 14SQCh. 20 - Prob. 15SQCh. 20 - If a cut or scrape becomes infected,...Ch. 20 - The adenoviruses that cause colds do not have a...Ch. 20 - Prob. 3CTCh. 20 - Prob. 4CT
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