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BBMB 405: FINAL EXAM
T/F
Regulation of the trp operon involves the sequential and coordinate production of five enzymes of tryptophan synthesis from 5 different mRNAs produce in equal concentrations.
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False; 5 enzymes are synthesized from a single polycistronic mRNA
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Explain the participation of the G protein (Golf) in olfaction.
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Activation upregulates cAMP in olfactory epithelium, opening cAMP-gated cation channels. This causes influx of Na+ and depolarization. Action potential results --> CNS --> smell
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Explain the participation of the G protein (transducin) in vision.
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Leads to activation of phosphodiesterase, which breaks down cGMP. Hyperpolarization of membrane occurs which signals CNS. Vision occurs.
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What's the mechanism by which addition of glucose to a lactose-containing medium containing growing E. coli decreases transcription of the lactase gene (glucose effect)?
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Addition of glucose decreases [cAMP] in E. coli.
At high [cAMP], catabolite activator protein (CAP) is bound to DNA, leading to tx of the lactase gene.
At low [cAMP], less CAP bound to DNA and lactase gene (operon) is transcribed slowly.
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When the nuclei of chicken globulin-producing cells were treated with pancreatic DNase, the adult globin genes were selectively destroyed, but the genes for embryonic globins and ovalbumin remained intact. Why?
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Adult globin genes are "disperse" and therefore, degraded by DNase. Embryonic globlins are "compact" and not susceptible to DNase activity and therefore remain intact
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Would you expect a zinc deficiency in eukaryotes to be associated with any sort of developmental abnormality? Explain in terms of Zn involvement in control of gene expression.
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Transcription of many eukaryotic genes is activated by proteins containing one or more zinc fingers, each of which is about 30 amino acids long with 2 cysteines and 2 histidines coordinated to a zinc ion. Zinc deficiencies could lead to developmental abnormalities due to its essential role in gene expression and cellular metabolism.
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Class I MHC proteins
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- contain an immunoglobulin fold motif
-contain a B-microglobulin chain
- contain one transmembrane chain
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Class II MHC proteins
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- contain an immunoglobulin fold motif
- contain two transmembrane polypeptide chains
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T-cell receptors
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- contain an immunoglobulin fold motif
- contain domains homologous to the V and C domains of immunoglobulins
- contain two transmembrane polypeptide chains
- are encoded by V, D, and J gene segments
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helper T-cell
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- detects foreign peptides presented on cell surfaces
- recognizes class II MHC protein plus peptide
- expresses CD4
- stimulates B lymphocytes and other cells
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cytotoxic T-cell
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-detects foreign peptides presented on cell surfaces
- recognizes class I MHC protein plus peptide
- expresses CD8
- lyses infected cells
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Why will a change from low to high iron status in your body result in greater rates of ferritin synthesis and lower rates of transferrin receptor synthesis?
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When iron ion concentrations increase, the iron response element (IRE) binding protein (IRP) binds iron ions. The IRB with attached iron ions cannot bind ferritin mRNA, so the mRNA is translated. At high iron concentrations, the IRP does not bind transferrin mRNA, so the mRNA is degraded. This decreases transferrin receptor synthesis and thus iron into cells.
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Even though tamoxifen binds the estrogen receptor, it does not have similar actions to those of estrogen, such as the promotion of breast cancer.
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Tamoxifen binding to estrogen receptor does not stimulate the signalling pathway. Coactivators don't bind and trigger increases in gene expression.
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Attenuation of expression of the trypt operon involves the intracellular concentration of trypt-tRNA. Explain this relationship.
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A trypt-tRNA shortage causes a stalling of ribosome movement while translating the leader sequence and allows continuous synthesis of mRNA from structural genes of the trypt operon. High concentration of trypt leads to higher concentrations of trypt-tRNA and formation of hairpins --> causes termination of transcription of trypt operon.
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Attenuation of expression of the trypt operon involves the intracellular concentration of trypt-tRNA. Explain this relationship.
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A trypt-tRNA shortage causes a stalling of ribosome movement while translating the leader sequence and allows continuous synthesis of mRNA from structural genes of the trypt operon. High concentration of trypt leads to higher concentrations of trypt-tRNA and formation of hairpins --> causes termination of transcription of trypt operon.
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Describe how attachment of an antigen to an immature B cell results in B cell activation.
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Lyk binds to phosphorylated ITAMs and phosphorylates other proteins that lead to proliferation of other B cells that secrete same IgM.
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Describe T cell dependent activation of B cells
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A pathogen is ingested by an APC and the pathogen's proteins are digested and attached to MHC II. This complex moves to the outside of the cell membrane.
When recognised by a T cell, the T cell proliferates and differentiates into effector and memory T cells.
Th cells then activate B cells, which subsequently produce antibodies.
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Explain the role of the small intestine in the synthesis and transport of retinal to your retina from dietary beta-carotene.
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B-carotene from the intestinal lumen goes into the intestinal cell.
2 retinal --> chylomicron in blood --> liver --> retinol in blood to retina
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The GpC "boxes" in the 1 kb upstream region of the globin gene in skeletal muscle is highly methylated wheras the same region in reticulocytes is methylated significantly less. What role does this observation suggest for the methylation of GpC boxes?
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Methylation of GpC boxes decreases expression of the globin gene
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Coactivators regulate the action of several transcription factors by altering the binding of histones to DNA and thus the remodeling of chromatin. Explain the suggested molecular mechanism of this effect of coactivators.
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histone tail in chromatin --(coactivator)--> acetylated histone tails in chromatin --> decreased affinity for DNA --> remodeling of chromatin
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A chronic change from low to high iron status in your body will result in ____ rates of ferritin synthesis and ____ rates of transferrin receptor synthesis in your liver.
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greater; lesser
increase in Fe --> more binding of Fe to IRE-BP --> IRE-BP does not bind to upstream IREs of ferritin mRNA or to downstream IREs of transferrin receptor protein --> higher translation of ferritin mRNA and lower transferrin receptor synthesis
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Differentiate between T cell receptors and antibodies - secretion from the synthetic cell
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T cell receptors are membrane-associated and are not secreted from cell
Antibodies may be secreted from cells as well as being associated with membrane
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Differentiate between T cell receptors and antibodies according to the following properties - involvement of protein of the MHC in the recognition of isolated foreign macromolecules (antigens).
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Antigens are processed internally and then presented on the surface of cells via the MHC proteins for recognition by antibodies.
Antibodies react directly with antigens.
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T cells vs antibodies - recognition of native (intact) foreign macromolecules
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T cell receptors recognize processed antigen. Antibodies will recognize intact antigen.
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Major biochemical role of the plasma cell in the immune response
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production of antibodies that are secreted
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major biochemical role of the T helper cell in humoral immune response
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binds B cells and stimulates their differentiation and proliferation; secretes cell growth factors (cytokines) that stimulate T cell growth and differentiation
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The concentration of estrogen is usually greater in its target tissue than in non-target tissues. T or F.
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True; receptors for estrogen are present in target cells and not in non-target tissues. Thus more estrogen will be concentrated in target tissues.
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The complement system facilitates removal of microorganisms from the blood. T or F.
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Complement activation causes formation of the membrane attack complex (MAC) that disrupts the microbe
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Degeneracy of the genetic code denotes the existence of codons consisting of only two bases. T or F.
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False;
Degeneracy denotes existence of multiple codons for a single amino acid.
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Is fMet-tRNAi required for protein synthesis in eukaryotic systems?
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No;
The initiator in eukaryotic systems is Met-tRNAi. Only prokaryotic systems require the Met-tRNAi to be formylated.
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Termination of protein synthesis requires a stop codon to be located at the P site of the large ribosomal subunit. T or F.
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False;
Termination occurs when the stop codon is located at the A site. Releasing factors bind to promote hydrolysis of the peptide from the tRNA in the P site.
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Explain the catalytic action of diptheria toxin.
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This toxin catalyzes the formation of an ADP-ribosyl derivative of translocase (EF-2), which irreversibly inactivates the translocase.
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Why are allolactose and cAMP both required for full expression of the lac operon?
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Allolactose binds the repressor and removes it from the operator region. cAMP binds to CAP, which interacts with RNA polymerase to increase its activity in initiation of transcription
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Enhancers must be upstream of the site of the preinitiation complez assembly in your liver cell to influence expression of your albumin gene. T or F.
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Enhancers may be upstream, down stream, or within the gene to influence albumin expression.
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Describe the skeletal muscle tropomyosin molecule, including its subunit composition, why it forms this type of molecule, and its overall role in contraction/relaxation.
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- TM molecule contains 2 subunits which form a long a-helical coiled-coil molecule
- The 2 a-helical strands form the two-stranded structure with positions "a" and "d", usually hydrophobic
- Each TM molecule is bound to and controls 7 actins along a strand of actin in the thin filament, and interacts with myosin in the absence of Ca.
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The thin filaments move closer to the sarcometric M-line during contraction. T or F.
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True |
Indicate why myosin and actin remain physically in touch/attached in rigor mortis.
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All of the ATP in the cytosol is used up, so ATP can't bind the substrate-binding site in each myosin head, which in living muscle releases the head from actin.
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The compliment system facilitates removal of microorganisms from the blood. T or F.
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True;
Compliment activation causes formation of the membrane attack complex (MAC) that disrupts the microbe
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