MB&B 107 Example Exam 2

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not true of T cells
they ahve membrane-bound immunoglobulins
true of T cells
they are derived from stem cells, they release various cytokines, they mature in the thymus
serotype
different pathogenic strains differing serologically by patient antisera
specialized transduction differs from generalized transduction by
the nature of the DNA that is packaged into the viral particle, whether donor bacterial DNA is attached to viral DNA or not, whether viral DNA is delivered to the recipient bacterium or not
IgM
is the first antibody class produced, both membrane-bound and secreted forms are produced, it contains μ heavy chains, it contains a J (joining) chain
bacterial endospores possess the following properties
chemical resistance, long lived, low metabolic activity, radiation resistance (not heat sensitivity)
bacterial pili
promote conjugation, host cell adhesion (don't resist antibody binding and neutralization)
the clonal selection hypothesis proposes that specific antibody is generated by
antigen binding stimulating proliferation of specific B cells
MHC receptors are important for the following function
presenting the peptide antigens to T cells
of the different genetic transfer mechanisms in bacteria, the one most important clinically for the spread of multiple antibiotic resistance is
conjugation
Which of the following mechanism(s) is used to create antibody diversity?
Immunoglobulin gene rearrangement of VJC and VDJC cassettes for light chain and heavy chain loci, respectively, Imprecise joining of cassettes during gene rearrangement, Random joining of different light and heavy chain combinations, Enormous number of different B cells that each can produce a different antigen-specific antibody
Positive selection of thymocytes (immature T cells):
The process whereby the TCR on maturing T cells is tested for its ability to recognize the unique group of MHC receptors present in an individual's body. Maturing T cells that are unable to productively bind peptide-MHC complexes die by apoptosis, while those pre-T cells that are able to productively bind peptide-MHC receptor complexes are allowed to mature and proceed on to negative selection.
Membrane efflux pump
a membrane transporter that actively pumps out normally toxic substances from the cytoplasm of cells.
MHC complex
a genetic locus encoding a series of polymorphic receptors that capture peptides and present them to lymphocytes for recognition by their T cell receptors. Class I MHC receptors are located on most nucleated cells and present peptides of intracellular origin (e.g. a virally infected cell) to cytotoxic T cells. Class II MHC receptors are present on professional antigen presenting cell types such as dendrites, macrophages, and B cells and present peptide of extracellular origin (e.g. extracellular bacteria or toxins) to helper T cells.
Conjugative plasmid
a plasmid that is capable of genetic transmission from a donor to a recipient cell.
Cytokine
a hormone-like family of proteins secreted by leukocytes that allows regulation of the immune system. (optional additional info: Cytokines fall into several different families: pro-inflammatory cytokines are important in promoting inflammation and immune activation, growth cytokines are important in the development and differentiation of cells of the immune system, toxic cytokines are important in cell killing, regulatory cytokines are important in down-regulating an immune response, and chemokines are important in the control of movement of leukocytes.)
Cytotoxic T cell
a type of lymphocyte of the T cell lineage that is specialized for killing virally-infected and cancer cells. (optional additional info: It uses a pore-forming toxin, perforin, as well a proteases called granzymes to induce killing by apoptosis.)
Transposase
an enzyme encoded by a transposon that catalyzes its movement from one DNA molecule (donor) to another (recipient).
Peptidoglycan
the cell wall of bacteria. It is comprised of long glycan chains that are crosslinked by peptide bridges in order to be the rigid stress-bearing, shape-retaining polymer of the bacterial cell.
Compare Gram positive and Gram negative cell architectures. Draw diagrams as necessary.
Gram positive bacteria have a thick, multilayer cell wall of peptidoglycan exterior to their cytoplasmic membrane. By contrast, Gram negative bacteria possess a thin cell wall of peptidoglycan that is sandwiched between their inner cytoplasmic membrane and their outer membrane, which is comprised of lipopolysaccharide on the outer leaflet of the outer membrane. Appropriate diagrams are given on page 4 of Lecture 5.
How does the immune system of a given individual learn "self" from "non-self"?
During negative selection in the bone marrow, pre-B cells that have BCRs (i.e. surface-bound immunoglobulins) that bind self antigens too tightly are eliminated by apoptosis. Thus, the mature population of B cells that emerges from the bone marrow possess BCRs that are not self-reactive. A similar type of negative selection occurs with pre-T cells in the thymus utilizing their TCR (T cell receptor).
Draw a picture of an antibody molecule such as IgG. Indicate the light and heavy chains as well as the genetically variable and constant regions. Also indicate the antigen-binding site(s). Indicate the region where the antibody would bind to an Fc receptor located on the surface of a macrophage.
An appropriate diagram is contained on page 3 of Lecture 4.
Using your knowledge of bacterial genetics, describe the evolution of an R factor.
An outline of the answer is as follows: a transposon inserts itself near an antibiotic resistance gene, followed by an insertion of a second copy of the transposon nearby, thereby creating a composite transposon. The composite transposon then inserts itself into a broad host-range conjugative plasmid to form an R factor. That R factor is transferred to many different pathogenic bacteria to give rise to multiple antibiotic resistance strains in the clinical environment.