D103 FINAL

What are the functions of a cyclin during the cell cycle ? 1. Activate a CDK 2. Direct a CDK to its targets. 3. Inhibit a CDK. 4. Control CDK activity through phosphorylation of the cyclin. 5. Control CDK activity through synthesis and destruction of the cyclin.

1,2,5

Compared to normal cells, which of the following signalling events would bealtered in a human male tissue culture cell line in which the gene encoding theandrogen receptor contained a missense mutation that abolishes the receptor'sDNA binding activity ? A. Genomic, but not non-genomic responses would be affected following addition of testosterone to a tissue culture dish containing the cells. B. Both genomic and non-genomic responses would be affected following addition of testosterone to a tissue culture dish containing the cells. C. The mutated androgen receptor would be present in the nucleus in the absence of ligand. D. Non-genomic, but not genomic responses would be affected following addition of testosterone to a tissue culture dish containing the cells.

A

Suppressor of Cytokine Signaling (SOCS) proteins negatively regulate cytokinesignaling by recruiting ubiquitin E3 ligases to the cytokine receptor. Which proteinperforms a similar function in signaling via TGF-beta / BMP receptors ? A. Smad7, an I-Smad B. Smad4, a Co-Smad C. Ski D. SnoN E. Smurf1 or 2, Ubiquitin E3 ligases.

A

The following graphs plot the cellular response measured in real time (x-axis,hours) by the % activation of a certain active effector protein (y-axis), for five celltypes (A to E) that are treated with three different concentrations of a signalmolecule. During the period indicated by the horizontal gray bar underneath the X-axis, the signal molecule is present in the culture media at a concentration of 1nM (dotted line), 5 nM (gray line), or 25 nM (black line). Note, in some graphs, thegray lines may be located close to, or the same as the black line. For cell line E,the gray line is immediately adjacent to the dotted line. Analyze the graphs thenanswer the following question.Which of the cell types A to E requires the smallest concentration of signal to elicit~100% activation of the effector ?

A

Which of the following changes occur after phosphorylation of a protein on tyrosineamino acids ? A. Increased molecular weight, increased acidity and possible interaction with a SH2 domain-containing protein B. Increased molecular weight, decreased acidity and possible interaction with a SH2domain-containing protein C. Increased molecular weight, decreased acidity and reduced likelihood of interaction with a SH2 domain-containing protein D. . Increased molecular weight, no change in charge and possible interaction with a SH2 domain-containing protein E. Increased molecular weight, increased acidity and reduced likelihood of interaction with aSH2 domain-containing protein

A

Which of the following events is required to form a pre-replicative complex inpreparation for DNA replication ? A. Dephosphorylation of ORC, Cdc6 and Cdt1 during M-phase. B. DNA polymerase function during G1. C. Activity of M-cyclins during S-phase. D. Binding of Cdt1 and Cdc6 to each other during G1. E. Phosphorylation of ORC, Cdc6 and Cdt1 during S-phase.

A

Which of the following is not an outcome of binding of an arrestin molecule to the cytoplasmic domain of an activated GPCR ? A. ncreased heterotrimeric GTPase-based signaling by the GPCR. B. Decreased signaling due to temporary endocytosis of the receptor. C. Altered signaling via the GPCR due to activation of new downstream signaling pathways. D. Decreased signaling by the GPCR due to endocytosis and destruction of the receptor. E. All of the above are outcomes of binding of an arrestin molecule to the cytoplasmic domain of an activated GPCR.

A

Which of the following statements is incorrect ? A. The beta/gamma subunit of a heterotrimeric GTPase determines the duration of openingof a potassium ion channel. B. Some heterotrimeric GTPases activate adenylyl cyclase while others inhibit it. C. The alpha and gamma subunits of a heterotrimeric GTPase have a post-translational modification. D. In a healthy cell, the concentration of GTP in the cytoplasm is much greater than theconcentration of GDP. E. An endocytosed GPCR can be degraded in the lysosome or returned to the cell surface.

A

You continue to study the results of your experiment you performed in Question 2.Which of the following conclusions can you make from your results as to what causes there to be more normal human male tissue culture cells in a dishapproximately 16 hours after treatment with testosterone ? A. None of the above conclusions is fully supported by the results. B. Wrinkled cells divide more rapidly. C. A wrinkled appearance 15 min after exposure to testosterone is necessary for cells to divide more rapidly. D. Smooth cells divide more rapidly.

A

You have discovered a new gene that encodes an unusual regulatory subunit ofPKA, which you name Ro. As with the R C version of PKA, Ro forms a dimer andinteracts with two molecules of the same catalytic subunit (C) found in PKA to forma Ro C heterotetramer. However, unlike the R in conventional PKA, each Rosubunit binds 8 molecules of cAMP. Which of the following properties would youpredict Ro C PKA would display compared to the conventional R C form of PKA? a. The dynamic range of activity of PKA with Ro subunits would occur over a narrower range of cAMP concentration. b. PKA with Ro subunits would become active at a lower concentration of cAMP. c. The dynamic range of activity of PKA with Ro subunits would over a wider range of cAMP concentration. d. Full activity of PKA with Ro subunits would occur at a higher concentration of cAMP.

A

What can an arrestin do to a GPCR ? A. An arrestin can bind to the GPCR and partially inhibit its signaling. B. An arrestin can stimulate a GRK to phosphorylate the GPCR. C. An arrestin can stimulate endocytosis of the GPCR D. An arrestin can activate MAPK signaling. E. An arrestin can sensitize a GPCR to increase its signaling strength.

A, C and D only.

The following graphs plot the cellular response (% activation of an effector protein(y-axis)) over time (x-axis, hours) for five cell types (A to E) that have been treatedwith three different concentrations of a signal molecule. During the time periodindicated by the horizontal gray bar underneath the X-axis, the signal molecule ispresent in the culture media at a concentration of 1 nM (dotted line), 5 nM (grayline), or 25 nM (black line). Note, in some graphs, the gray lines may be locatedclose to, or the same as the black line. Analyze the graphs then answer thefollowing question.Which cell type shows evidence of a response to the signal that isconsistent with a bi-stable switch ? A. E B. A C. B D. D E. C

B

The following graphs plot the cellular response (% activation of an effector protein(y-axis)) over time (x-axis, hours) for five cell types (A to E) that have been treatedwith three different concentrations of a signal molecule. During the time periodindicated by the horizontal gray bar underneath the X-axis, the signal molecule ispresent in the culture media at a concentration of 1 nM (dotted line), 5 nM (grayline), or 25 nM (black line). Note, in some graphs, the gray lines may be locatedclose to, or the same as the black line. Analyze the graphs then answer thefollowing question.Which cell type shows the lowest sensitivity to the signal ? A. C B. E C. A D. B E. D

B

What directly causes the G-alpha subunit of a heterotrimeric GTPase to release itsGDP ? A. Binding of hormone to the GTPase B. Interaction of the G-alpha subunit with a ligand-bound GPCR C. Separation of the G-beta/gamma subunits from the alpha-subunit. D. Binding of the G-alpha subunit to an effector protein. E. A conformational change in the G-beta/gamma subunits.

B

What is the receptor for nitric oxide (NO) in blood vessels ? A. Guanylyl cyclase in endothelial cells. B. Guanylyl cyclase in smooth muscle cells. C. Cyclic GMP in smooth muscle cells. D. Nitric oxide synthase in endothelial cells. E. Calmodulin in endothelial cells.

B

Which of the following could decrease signaling via phospholipase C? A. Release of Ca into the cytosol B. Dephosphorylation of IP C. Increased synthesis of DAG D. Opening of TRP or Orai1 Ca channels E. Decreased synthesis of IP kinase

B

Which of the following effects is least likely to be mediated by a scaffolding protein? A. Decrease likelihood of crosstalk between signaling pathways that share a commonkinase. B. Decrease specificity of interactions between intracellular signaling proteins. C. Allow rapid negative feedback of a signaling response. D. Increase the local concentration of signaling components.

B

Which of the following is NOT considered to be a common second messenger incell signaling ? A. Diacylglycerol B. Adenosine triphosphateInositol triphosphate C. Cyclic adenosine monophosphate D. Ca

B

Which of the following might be expected to directly turn off calmodulin activity ? A. Turning off a plasma membrane potassium ion channel. B. Activating a plasma membrane calcium ion pump. C. Opening a plasma membrane voltage gated sodium ion channel. D. A rapid increase in the concentration of GTP in the cytoplasm. E. Release of GDP from the activated calmodulin.

B

Which of the following statements is true? A. Unlike the androgen receptor, the retinoic acid receptor (RAR) does not bind a co-activator protein. B. An androgen receptor that lacks a DNA binding domain can still signal. C. A retinoid hormone receptor lacking a ligand binding domain would be unable to regulate gene expression. D. Thyroid hormone receptors are located in the cytosol until they bind to a ligand.

B

You are working in a lab as a Bio199 student studying the function of a novel genethat encodes a cell surface transmembrane receptor in Drosophila (fruit-fly).Drosophila mutants that lose the function of this receptor show dramaticdevelopmental defects involving loss of legs. Your boss asks you to start analyzingthe mouse version of the gene encoding the related cell surface receptor. Whatmight you discover when you undertake this task ? A. The mouse genome doesn't appear to have a gene that can encode a protein related tothe receptor found in Drosophila. B. The mouse genome has several genes whose exon coding sequence differ slightly from each other, but each gene is predicted to encode a receptor that is similar to the receptor found in Drosophila. C. The mouse genome appears to also have only one gene encoding the transmembrane receptor and its amino acid sequence is identical.

B

Which cell type(s) show evidence of receptor de-sensitization ?

B and C

22-2 Based on your knowledge of cellular signaling you are asked to develop a strategy to boost the concentration of red blood cells (erythrocytes) in cancer patients. Which of the following combinations of changes in activity of targets might produce the best strategy?A. Increase activity of SOCS proteins; decrease activity of Epo receptor; increase activity of SHP1 phosphatase. B. Decrease activity of SOCS proteins; increase activity of Epo receptor; increase activity of SHP1 phosphatase. C. Decrease activity of SOCS proteins; increase activity of Epo receptor; decrease activity of SHP1 phosphatase. D. Decrease activity of SOCS proteins; decrease activity of Epo receptor; decrease activity of SHP1 phosphatase. E. Increase activity of SOCS proteins; increase activity of Epo receptor; increase activity of SHP1 phosphatase.

C

23-3 Which of the following describes a negative feedback effect mediated by a scaffolding protein ? A. The activity of phospholipase Cbon PKC. B. The activity of Ras on MAP3K. C. The activity of PKA on a cAMP PDE. D. The activity of STATs on SOCS proteins.

C

The most abundant source of Ca within a cell is found within the lumen of theER. During certain signaling events, the second messenger inositol 1,4,5-triphosphate (IP ) can trigger release of Ca from the lumen of the ER into thecytosol. Subsequently, the cell must restore the Ca concentration within the ER lumen in preparation for the next IP -mediated signaling event.How does the cell "sense" that the ER-lumenal concentration of Ca hasdecreased ? A. An increase in Ca within the cytoplasm induces a conformational change in calmodulin,which activates pumps that pump calcium out of the cell. B. A decrease in Ca within the lumen of the ER causes ER Ca store pumps to move Ca back into the lumen of the ER. C. A decrease in Ca within the lumen of the ER causes a conformational change in an EF hand domain located within the lumen of the ER. D. An increase of Ca within the cytoplasm causes Orai1 calcium channels within the plasma membrane to oligomerize.

C

What event immediately precedes activation of S-phase cyclin-CDK ? A. A kinase that activates an inhibitor of S-cyclins. B. A kinase that activates an activator of S-cyclins. C. Ubiquitination and degradation of an inhibitor of S-cyclins. D. A phosphatase that inhibits an inhibitor of S-cyclins. E. A phosphatase that activates an activator of S-cyclins.

C

Which event is required for cell cycle arrest following DNA damage involvingdouble-strand breaks ? A. Inhibition of ATM/ATR kinases. B. Dephosphorylation of p53. C. Transcription of a CKI. D. Binding of MDM2 to p53. E. Destruction of cyclins by ubiquitination.

C

Which of the following "feedback" systems would be suited to allow a cell to respond to long-term but not short-term signals ? A. A positive feedback loop. B. A negative feedback loop. C. A feed-forward loop. D. None of the above feedback systems is suited to allow a cell to respond to a long-term but not short-term signal.

C

Which of the following can act as a GAP for a heterotrimeric GTPase ? A. A GPCR B. GDP C. The target of the alpha subunit of the GTPase D. The beta-gamma subunits of the GTPase E. A GRK

C

Which of the following describes an example of positive feedback that occursduring the cell cycle ? A. Activation of a CDK by a cyclin. B. Phosphorylation of Sic1 by G1/S Cyclin/CDK. C. Stimulation of transcription of E2F gene by E2F protein. D. Phosphorylation of Rb by G1-Cyclin/CDK E. None of the above is an example of an event involving positive feedback.

C

Which of the following events normally activates a GDP-bound GTPase ? A. GTP hydrolysis by the protein B. Activation of an upstream GTPase-activating protein C. Activation of an upstream guanine nucleotide exchange factor D. Phosphorylation of a bound GDP molecule by an upstream kinase E. Pi release after GTP hydrolysis

C

Which of the following proteins is the product of an immediate early geneexpressed following mitogenic stimulation of cell-cycle entry ? A. E2F B. G1-cyclins C. Myc D. Rb E. All of the above

C

You continue to study the results of your experiment you performed in Question 2. Which of the following explanations would best explain why cells in some dishesbecame wrinkled 15 min after addition of testosterone ? A. Transcription of target genes by an activated androgen receptor caused a change in theactin cytoskeleton. B. Transcription of target genes by an activated estrogen receptor caused a change in theactin cytoskeleton. C. Non-genomic responses by an activated androgen receptor caused a change in the actincytoskeleton. D. Non-genomic responses by an activated estrogen receptor caused a change in the actincytoskeleton. E. Non-genomic and genomic responses by an activated androgen receptor caused a change in the actin cytoskeleton.

C

You continue to study the results of your experiment you performed in Question 2.Which of the following conclusions about activity of the X-linked androgen receptor(AR) in the two new cell lines might best fit with your results ? A. The gene encoding the AR in cell line Unk#1 is not being expressed at all. B. The gene encoding the AR in cell line Unk#2 has a mutation that affects the ability of theAR to bind to DNA. C. The gene encoding the AR in cell line Unk#1 has a mutation that affects the ability of theAR to bind to DNA. D. None of the above conclusions fits with the results obtained. E. The gene encoding the AR in cell line Unk#2 is not being expressed at all.

C

Which of the following types of proteins interacts with and thereby activates Ras ? A. A kinase B. A phosphatase C. A GEF D. A GAP E. A GTPase

C.

Molecule 'S' can bind to a GPCR on the surface of mammalian cells, stimulatingthem to form actin stress fibers. You have a solution of "S", as well as a solution ofGTP-gamma-F, a fictitious non-hydrolysable analog of GTP that can bind toheterotrimeric GTPases. You treat mammalian cells in one dish with molecule 'S'only. At the same time, you treat a second dish containing the same type of cellswith both molecule 'S' and GTP-gamma-F. You immediately perform a time-lapselive-cell fluorescence microscopy analysis to image the status of the fluorescingactin cytoskeleton in the same living cell in each of the two dishes immediatelybefore (t=0 min) and at three times (5, 10, 15 min) after addition of 'S', or 'S' plusGTP-gamma-F. (Note, for the purpose of this question, assume (i) that the plasmamembrane is freely permeable to GTP-gamma-F; (ii) that GTP and GTP-gamma-Feach bind with the same affinity to heterotrimeric G-proteins, and that GTP-gamma-F has no effect on Rho.)Which cell received which compounds ? A. Cell A received 'S' plus 'GTP-gamma-F; Cell B received 'S' only. B. Cell B received 'S' plus 'GTP-gamma-F; Cell A received 'S' only. C. It is impossible to predict which cell received the different compounds based on theinformation provided.

Cell A received 'S' plus 'GTP-gamma-F; Cell B received 'S' only.

A cell expresses a transmembrane protein that is cleaved at the plasmamembrane to release an extracellular fragment. The fragment binds to receptorproteins on nearby cells and activates signaling pathways resulting in altered geneexpression patterns in the cells. Which of the following best describes this form ofintercellular signaling ? A. Contact-dependent B. signaling Endocrine C. signaling Synaptic signaling D. Paracrine signaling

D

Cholera toxin ADP-ribosylates the α subunit of stimulatory G protein (G ), therebyblocking GTP hydrolysis. By contrast, pertussis toxin ADP-ribosylates the α subunit ofinhibitory G protein (G ) and prevents its interaction with the GPCR. What is the effect ofthese toxins on the concentration of intracellular cAMP? A. Cholera toxin tends to decrease cAMP concentration, whereas pertussis toxin tends toincrease cAMP concentration. B. They both tend to decrease cAMP concentration. C. Cholera toxin tends to increase cAMP concentration, whereas pertussis toxin tends todecrease cAMP concentration. D. They both tend to increase cAMP concentration

D

Evolutionary biology studies have identified the most invariant (conserved) aminoacids found within the SH2 domain family. Which of the following is true regardingthese invariant amino acids ? A. The invariant amino acids generally have negatively charged side chains. B. The amino acids at these sites are generally hydrophobic. C. These sites evolve (change) relatively quickly because they have critical functions. D. These amino acids have an important function in allowing binding of the SH2 domain to aphosphorylated tyrosine. E. Mutation in these sites generally keeps the protein functional.

D

Molecule "Y" is a second messenger, whose lifespan in cells is 10 min. Following stimulation of a cell surface receptor, production of Y increases one hundred-fold. An increase in concentration of Y is required to mediate a decrease in the activity of enzyme "Z". What best describes the effect on this signaling pathway if the lifespan of Y was changed to 10 sec ? A. Activity of Z will increase more rapidly. B. Activity of Z will decrease more slowly. C. Activity of Z will increase more slowly. D. Activity of Z will decrease more rapidly.

D

Select the correct phrase to complete the following sentence. "All nuclear hormonereceptors ..." A. bind to steroid hormones. B. are transcriptional activators when bound to their ligand. C. are transcriptional repressors in the absence of their ligand. D. have ligand-binding and DNA-binding domains, and can directly bind to DNA. E. are cytosolic proteins that enter the nucleus upon ligand binding.

D

Study the signaling pathway below, which involves two different receptors. Assume that a protein is active only when it is activated, but not when it is inhibited, by its upstream signaling molecule(s). Activation and inhibition are indicated by lines with an arrowhead or a "T" bar, respectively. Assume that the "Transcription Regulator" can be activated by either the binding protein or the kinase that are immediately upstream of the Transcription Regulator. Under which of the following conditions is target-gene "X" expression and the cellular response induced ? A. Only in the presence of signal 2 but not signal 1. B. Only in the presence of both signals (1 and 2). C. In the presence of either or both signals (1 or 2). D. In the presence of either signal but not both of them. E. Only in the absence of both signals.

D

What is the most likely effect of greatly increasing the activity of cAMPphosphodiesterase (cAMP PDE) throughout the cell ? A. G alpha cannot be activated. B. Signaling via the G beta/gamma is blocked. C. PKG cannot be activated. D. The catalytic subunits of PKA cannot dissociate from the regulatory subunit. E. cAMP-mediated signaling is not affected.

D

Which of the following best describes how an I-Smad (e.g. Smad7) participates in regulation of signaling via TGF-b family member receptors ? A. The I-Smad co-associates with R-Smads and Co-Smads (e.g. Smad 4) and prevents activation of gene expression in the nucleus by interfering with binding to DNA. B. The I-Smad binds with R-Smads only and prevents R-Smads from activating gene expression in the nucleus. C. The I-Smad binds the the Type-I receptor and once phosphorylated interacts with and prevents R-Smads from being imported to the nucleus to mediate gene expression. D. The I-Smad binds to the Type-I receptor but cannot be phosphorylated by it, thereby preventing interaction of R-Smads with the receptor.

D

Which of the following best explains how the NLS of a STAT protein normallybecomes exposed during a signaling event ? A. Through mono-ubiquitination by a SOCS protein. B. Through phosphorylation of the STAT by a serine kinase, causing it to associate with a receptor. C.Through dephosphorylation of the STAT by a phosphatase, causing a conformational change that exposes the NLS. D. Through phosphorylation of the STAT causing it to dimerize. E. Through binding of the STAT to a JAK, causing a conformational change that exposes theSTAT's NLS.

D

Which of the following is NOT a common mechanism used to regulate activity ofsignaling proteins ? A. Binding of another molecule to the signaling protein. B. Masking of a NLS signal in the signaling protein by another protein. C. Degradation of the signaling molecule by proteolysis. D. Uptake of the signaling protein by the ER. E. Covalent modification of a protein involved in a signaling pathway (e.g. phosphorylation)

D

Which of the following is an early consequence of activation of phospholipase C-β(PLCβ) by the G trimeric GTPase ? a. Elevation of intracellular cAMP levels, leading to the activation of protein kinase A b. Elevation of intracellular cGMP levels, leading to the activation of protein kinase G c. Elevation of PIP levels in the plasma membrane, leading to the activation of protein kinase B d. Elevation of intracellular Ca levels, leading to the activation of protein kinase C e. Elevation of IP in the plasma membrane, leading to the activation of protein kinase D

D

Which of the following statements about CKI proteins is false ? A. They are degraded via poly-ubiquitination. B. They are synthesized during each cell cycle. C. They are essential for the function of several checkpoints. D. They activate mitotic CDK.

D

Which protein in the TNF-alpha signaling pathway serves a similar function toHsp90 in the steroid hormone signaling pathway ? A. E3 ligase B. p50 C. p65 D. I-kB alpha E. I-kB kinase

D

Which statement best describes how molecular complementarity enablesspecificity during a signaling event ? A. he molecular shape of two molecules should have a large amount of overallcomplementarity that involves strong interactions at multiple different sites. B. The molecular shape of two molecules should have a small amount of complementarity. C. The molecular shape of two molecules should have a large amount of overall complementarity that involves covalent interactions at multiple different sites. D. The molecular shape of two molecules should have a large amount of overall complementarity that involves weak interactions at multiple different sites.

D

You are given a novel drug that inhibits the activity of a GPCR kinase (GRK)specific for GPCR's that bind adrenaline (epinephrine). You know that adrenalineincreases heart rate and activates adenylyl cyclase leading to breakdown ofglycogen in muscle. You inject two rats. Rat #1 is given an injection of the noveldrug followed by adrenaline, while rat #2 is injected with adrenaline only. Which of the following would you find when you analyze the rats 5 min after injection of adrenaline ? A. Rat # 1 has increased glycogen and increased cAMP in muscle, and increased heart rate relative to Rat #2 B. Rat # 1 has decreased glycogen and decreased cAMP in muscle, and decreased heart rate relative to Rat #2 C. Rat # 1 has decreased glycogen and increased cAMP in muscle, and decreased heart rate relative to Rat #2 D. Rat # 1 has decreased glycogen and increased cAMP in muscle, and increased heart rate relative to Rat #2 E. No difference in levels of glycogen and cAMP in muscle, and heart rate in rat #1compared to rat #2

D

You are working in a biochemistry lab as a Bio199 student. After many daysworking in a cold room, you have managed to purify a single protein from extractsfrom human fibroblasts. You wish to find out the sub-cellular location of yourprotein in human fibroblasts, so you send your protein to a company that makespolyclonal antiserum by immunizing rabbits with your protein. About two monthslater, you receive a package from the company that contains two tubes shippedwith ice-packs to keep the contents fresh. One tube (A) contains serum taken fromthe rabbit before it was immunized with your purified protein. The second tube (B)contains serum taken from the same rabbit 8 weeks after it had been immunizedtwice with your protein, with a gap of 4 weeks between injections. Using yourknowledge from the first half of D103, you perform an immunofluorescenceanalysis of fixed human fibroblast cells using diluted serum from the two differenttubes (A and B). You fix two identical samples of your fibroblasts that were grownon glass slides and then incubate one with serum from tube A and the other usingserum from tube B. After rinsing the slides, you incubate both with the samefluorescently labeled anti-rabbit secondary antibody. You then examine your cellsunder a fluorescence microscope. Human fibroblast cells reacted using serum from tube A show weak fluorescence. at the plasma membrane only, while the same human fibroblast cells reacted withserum from tube B show fluorescence in the nucleus as well as weak fluorescenceat the plasma membrane.Based on these results, what do you predict is the more likely subcellular locationof your purified protein in human fibroblasts ? Also, why did the company alsoprovide you with a sample of serum from the rabbit before it was immunized withyour purified protein ? A. The purified protein is more likely to be located in at the plasma membrane. The companysent a sample of the serum taken from the rabbit before immunization for use as apositive control in the immunofluorescence analysis. B. The purified protein is more likely to be located in at the nucleus. The company sent asample of the serum taken from the rabbit before immunization for use as a positivecontrol in the immunofluorescence analysis. C. The purified protein is more likely to be located in at the plasma membrane. The companysent a sample of the serum taken from the rabbit before immunization for use as anegative control in the immunofluorescence analysis. D. The purified protein is more likely to be located in the nucleus. The company sent asample of the serum taken from the rabbit before immunization for use as a negativecontrol in the immunofluorescence analysis.

D

You continue to study the results of your experiment you performed in Question 2.Which of the following explanations would best fit your results concerning theappearance of the cells 15 min after addition of testosterone ? A. Unk#1 cells have not undergone a non-genomic response to testosterone, while Unk#2cells have undergone a non-genomic response to testosterone. B. Unk#1 cells have undergone a non-genomic response to testosterone, while Unk#2 cells C. have not undergone a non-genomic response to testosterone.Unk#1 cells have not undergone a genomic response to testosterone, while Unk#2 cellshave undergone a genomic response to testosterone. D. Unk#1 cells have undergone a genomic response to testosterone, while Unk#2 cells havenot undergone a genomic response to testosterone. E. Both the Normal plus T cells and Unk#1 cells have undergone a genomic response totestosterone.

D

Which of the following phosphoinositides can bind to a PH-domain-containingprotein ?

D,E

Which of the following is not a general principle of signaling in multi-cellular eukaryotes ? D. Signaling pathways seldom share components with other pathways. A. Many signals can be amplified or dampened by the cell. C. A signal can activate more than one signaling pathway in a cell. E. Cells are constantly bombarded by signals. B. Some cells respond to the same signal in different ways.

D. Signaling pathways seldom share components with other pathways.

Sort the following events to reflect the normal order in which they occur in G-protein-coupled receptor signaling leading to transcription of genes that have acAMP response element. Your answer would be a four-letter string composed ofletters A to D only, e.g. ACBD. (A) Binding of CREB to PKA (B) Binding of cAMP to PKA (C) Dissociation of PKA into catalytic and regulatory subunits (D) Activation of adenylyl cyclase DBAC DBCA DCAB DCBA BCDA

DBCA

24-1 Which of the following statements concerning the cellular machinery that controls the cell cycle is false? A. The concentration of cyclins change during the cell cycle, while CDK remains relatively stable. B. M-cyclin / CDK must be inactivated before the cell can complete mitosis. C. CDK's become fully active upon binding a cyclin. D. Both G1-CDK and G1/S-CDK can phosphorylate Rb. E. The major function of active G1-CDK is to transcribe G1/S-cyclins.

E

24-2 Which of the following statements about M-cyclin proteins is false ? A. They are degraded via poly-ubiquitination. B. They are synthesized during each cell cycle. C. They are present in the cell during G2. D. They activate mitotic CDK. E. Their presence is required for the cell to exit mitosis.

E

The following graphs plot the cellular response (% activation of an effector protein(y-axis)) over time (x-axis, hours) for five cell types (A to E) that have been treatedwith three different concentrations of a signal molecule. During the time periodindicated by the horizontal gray bar underneath the X-axis, the signal molecule ispresent in the culture media at a concentration of 1 nM (dotted line), 5 nM (grayline), or 25 nM (black line). Note, in some graphs, the gray lines may be locatedclose to, or the same as the black line. For cell line E, the gray line is immediatelyadjacent to the dotted line. Analyze the graphs then answer the following question.Which of the cell types A to E shows the lowest sensitivity to the signal ? (note -sensitivity is defined as any activation of the effector protein in response to asignal)

E

Which domains would you expect to find in an adaptor signaling protein capable ofsimultaneously binding to (i) a phospho-tyrosine; (ii) a phosphatidyl-inositol (3,4,5)tri-phosphate (PI(3,4,5)P ) and (iii) a di-acyl glycerol (DAG) ? A. A protein containing a FYVE, a 14-3-3, and a SH2 domain. B. A protein containing a C1, a FYVE and a WW domain. C. A protein containing a SH2, a FYVE and a PH domain. D. A protein containing a SH3, a Tubby and a C1 domain. E. A protein containing a SH2, a C1 and a PH domain.

E

Which of the following events can restore the sensitivity of a de-sensitized GPCR ? A. Endocytosis of the GPCR B. Continuous stimulation of the GPCR C. Binding of a GRK to a GPCR D. Binding of ATP to the cytosolic region of the GPCR E. De-phosphorylation of the GPCR

E

Which of the following events is an example of negative feedback in a signalingpathway ? A. Binding of a GEF to a monomeric GTPase. B. Binding of the beta/gamma subunits to an alpha subunit of a heterotrimeric GTPase. C. Binding of ORAI to STIM1. D. Binding of a GDP-bound heterotrimeric GTPase to adenylyl cyclase. E. Calcium-calmodulin mediated activation of a membrane localized Ca2+ pump that movesCa2+ out of the cytoplasm.

E

Which of the following molecules could best be categorized as functioning by"Transducing and Amplifying" a signal ? A. Retinoic Acid Receptor (RAR) without ligand in nuclear hormone receptor signaling. B. Hsp90 in androgen receptor signaling C. E3 ligase in TNF-alpha signaling D. Citrulline in NO signaling E. Guanylyl cyclase in NO signaling

E

Which statement about cell surface receptors with intrinsic or associated enzymeactivity is false ? A. Some receptors dimerize before binding ligand B. The genes for some receptors encode kinase activity, while others do not C. Receptors commonly recruit signaling proteins via phosphorylation of the receptor's cytoplasmic region. D. Receptors always undergo a conformational change upon binding of ligand E. None of the above statements is false

E

Which of the following statements describes a method by which signaling via TGF-beta and BMP receptors is decreased ? I SMAD-mediated expression of a protein that acts in the nucleus to block SMAD-dependent signaling. II SMAD-mediated expression of a SMAD that cannot be phosphorylated by aTGF-beta/BMP receptor complex. III SMAD-mediated histone acetylation of genes whose expression are regulatedby SMADs. IV SMAD-dependent phosphorylation of the cytoplasmic receptor tails of type-ITGF-beta/BMP receptors.

I and II

In addition to control of cell growth and division, Mitogen-Activated Protein Kinases (MAPKs) have important functions in several other important cellular processesincluding differentiation, survival and apoptosis. Consequently, to minimize the riskof developmental defects and cancer, the control of MAPK activation must becarefully regulated. Which of the following helps to minimize inappropriate MAPK activity ? I MAPKs are only activated by MAP2Ks. II MAPKs can only be activated after release of ADP. III MAPKs must be phosphorylated on both threonine and tyrosine to become fullyactive.

I and III only

Which of the following statements concerning STAT proteins is / are true ? I STATs can interact with proteins via a phospho-tyrosine on the interactingprotein. II STATs can interact with proteins via a phospho-serine on the interacting protein. III STATs can bind to a phosphorylated JAK. IV STATs can form homo-dimers.

I and IV

Which of the following receptor signaling pathways use phosphorylation to causeexposure of a NLS so that a signaling protein can be targeted to the nucleus ? I TNF-alpha signaling II RTK Signaling III TGF-beta signaling IV Cytokine signaling

I, III and IV

In some signaling pathways, phosphorylation of amino acids in the cytoplasmicdomain of the cell surface transmembrane receptor increases the affinity betweenthe cytoplasmic domain of the receptor and non-transmembrane cytoplasmicproteins. In turn, interaction of the non-transmembrane cytoplasmic proteins withthe cytoplasmic tail of the receptor causes the non-transmembrane proteins tobecome phosphorylated, which allows the non-transmembrane proteins to directlyregulate transcription.Which domains and motifs might you find in the "non-transmembrane proteins"described in the above statement ? I SH2 domain II SH3 domain III GTP binding domain IV MH2 domainV NLS motif

I, IV and V

2-3 Ras GTPase was first discovered as being a gene that can change normal cells into cancer cells. Ras is normally activated by a receptor tyrosine kinase (RTK). However, in many cancers the Ras gene is mutated in a way that makes its signaling hyperactive. The hyperactive Ras conveys signals that drive cell division and tumor growth. You have learned that activated Ras can bind MAP3K, which in turn activates MAP2K, which activates MAPK that targets effector molecules leading to cell growth and division. What types of mutations in a Ras gene could produce hyperactive signaling Ras ? I - Missense mutations that stimulate Ras to bind Ras GTPase-activating proteins. II - Missense mutations that decrease the ability of Ras to hydrolyze GTP. III - Missense mutations that prevent Ras from binding to Ras-GEF.

II

Signaling via cytokine receptors can occur via STATs and this signaling can be negatively regulated by SHP1. Assume that the SH2 domain in a STAT and the SH2 domain in SHP1 interact with the same phosphorylated amino acid in the C-terminal tail of a cytokine receptor. Also assume that when SHP1 is expressed, there is only one molecule of SHP1 for every 10 molecules of STAT. Despite this, SHP1 is extremely efficient at inactivating STAT-dependent signaling via the cytokine receptor. Which of the following statements would you predict to be true ? I The STAT's SH2 domain has higher affinity for the phosphorylated amino acid compared to SHP1's SH2 domain. II The STAT's SH2 domain has lower affinity for the phosphorylated amino acid compared to SHP1's SH2 domain. III The STAT's SH2 domain has the same affinity for the phosphorylated amino acid compared to SHP1's SH2 domain. IV SHP1 protein is likely to be expressed in cells immediately before the cytokine receptor is activated. V SHP1 protein is likely to be expressed in cells after the cytokine receptor is activated. I and V II and IV III and V II and V I and IV

II and V

Which of the following events is an example of negative feedback in a signalingpathway ? I Binding of the beta/gamma subunits to an alpha subunit of a heterotrimericGTPase. II Binding of an I-Smad to a TGF-beta type-I receptor. III Binding of a GEF to a monomeric GTPase. IV Binding of a GAP to a monomeric GTPase. V Calcium-calmodulin mediated activation of a membrane localized Ca pumpthat moves Ca out of the cytoplasm.

II, IV and V

You are a Bio199 student working in a lab that studies nuclear hormone receptors(yipee !). The clinical fellow working with you has taught you how to culture (growand divide) human fibroblast cells in tissue culture dishes. She gives you two newcell lines developed from two new male patients seen by the clinic and asks you toinvestigate the response of each cell line to having testosterone added to thetissue culture media in their dishes. So that you can compare the results obtainedto those expected from a normal male human cell line, she asks you to use anappropriate negative and positive control in your experiment.Your prepare four dishes of cultured human fibroblast cells. One dish contains cellsfrom the first new male patient (Unk#1) while a second dish contains cells from thesecond new male patient (Unk#2). The two remaining dishes each contain cellsfrom the same known normal human male. Your prepare all four dishes to containthe same number of cells.Next, you add testosterone (T) to each dish containing the two new cell lines(Unk#1 and Unk#2). You also add testosterone to one dish containing a knownnormal human cell line (Normal plus T), but you do not add testosterone to thesecond dish containing the normal human cell line (Normal without T). After addingthe testosterone, you watch the cells in each dish using a microscope for 15minutes and record their morphology. You then replace the dishes in the tissueculture incubator. The next day you re-examine each of the dishes and recordsome more results. You take a coffee break and review your results which includethe following. Which dish is your positive control for a cellular response to testosterone, andwhich dish is your negative control ?

Positive control is Normal plus T; Negative control is Normal without T

In your molecular biology class you make two different cDNAs. The first cDNA expressesa green fluorescence protein (GFP) fused to the retinoid hormone receptor. The secondcDNA expresses a red fluorescent protein (RFP) fused to the glucocorticoid receptor. Youexpress both cDNA's in the same mammalian cell in a dish and you examine theirappearance using a microscope equipped with fluorescence optics. You then add retinoidand glucocorticoid ligands to the dish and wait for 30 min before re-examining the cells.Which colors would be seen in the nucleus and the cytosol before and after addition of theligands ?

Red fluorescence in cytoplasm and green fluorescence in nucleus before addition ofligands; red and green fluorescence in nucleus after addition of ligands.

Indicate true (T) or false (F) for the statements below regarding cellular signalingmediated by nitric oxide (NO). ( ) Once produced, NO can diffuse to neighboring cells. ( ) The lifetime of NO is 5 - 10 minutes. ( ) NO normally decreases cGMP concentration by directly activatingcGMP phosphodiesterase. ( ) The drug Viagra® counteracts the effects of NO on penile bloodvessels.

TFFF

Molecule "X" is a second messenger, whose lifespan in cells is 1 min. Followingstimulation of a cell surface receptor, production of X decreases one hundred fold. A decrease in concentration of X is required to mediate an increase in the activityof enzyme "Y". What best describes the effect on this signaling pathway if thelifespan of X was 15 min ? a. Activity of Y will decrease more rapidly. b. Activity of Y will decrease more slowly. c. Activity of Y will increase more rapidly. d. Activity of Y will increase more slowly. e. Activity of Y will remain unnchanged.

d

A kinase modifies the side chain of two serine and three threonine amino acids ina protein. Which of the following statements are true or false regarding the non-phosphorylated protein and the phosphorylated protein ? 1. The phosphorylated protein has a smaller molecular mass than the non-phosphorylated protein. 2. The overall (net) charge of the non-phosphorylated protein is more positivecompared to the phosphorylated protein. 3. The phosphorylated protein might be more likely to interact with proteins 4. The non-phosphorylated protein might be more likely to interact with proteinscontaining a SH2 and a PTB domain.

ftff