2018 Cell-Signalling MCQ QP+MS

2018 Cell Signalling MCQ2018 / H2 / ACJC PRELIM / P1 Q231Nerve cells in the brain communicate by chemical molecules known as neurotransmitters. The following events, in the order shown, describe how binding of a neurotransmitter to a nerve cell will elicit a cellular response.1Neurotransmitter binds to a G-protein linked receptor (GPLR) at the cell surface↓2A change in conformation of the GPLR allows the binding of a G protein to its intracellular domain↓3G protein releases a GDP molecule in exchange for GTP↓4The alpha subunit of the G protein dissociates from the other subunits↓5The alpha subunit of the G protein activates adenylyl cyclase, which in turn converts ATP into cyclic AMP (cAMP)↓6cAMP activates protein kinase A (PKA), which in turn phosphorylates transmembrane protein channels↓7Phosphorylated protein channels open, allowing the facilitated diffusion of specific ions into the nerve cellHow many of the events allow for the amplification of signal to occur?A3B4C5D6

2018 / H2 / ACJC PRELIM / P1 Q242The figure shows the levels of glucose, insulin and glucagon found in blood, before and after a carbohydrate-containing meal was ingested. Which row correctly identifies the events occurring at the respective timings?TimingEventsA60 minutes before mealGlucagon results in the activation of glycogen phosphorylase, leading to increased rates of glycogenolysis in liver cells and an increase in blood glucose levels.B30 minutes before mealGlucagon binds to G protein-linked receptors, leading to the activation of G proteins due to the hydrolysis of GTP molecules. Cellular responses lead to the maintenance of blood glucose levels.CAt the start of meal (0 minutes)Insulin binds to tyrosine kinase receptors, resulting in the cross-phosphorylation of receptor monomers. Cellular responses lead to a decrease in blood glucose levels.D60 minutes after mealInsulin results in the translocation of glucose transporters to the cell surface, leading to increased rates of glucose uptake in muscle cells and a decrease in blood glucose levels.

2018 / H2 / AJC PRELIM / P1 Q233Ethylene gas is a plant hormone that regulates plant growth, development and response to environmental stress. It is produced from leaves, roots, stems, flowers and especially ripened fruits. Plants have various ethylene receptors which are located in the endoplasmic reticulum (ER). The diagram shows the ethylene signalling pathway. Ethylene receptors are dimeric, transmembrane proteins, with a copper-containing ethylene-binding domain and a domain that interacts with a cytoplasmic protein called CTR1. Absence of ethylenePresence of ethyleneactive ethylene receptorcopper ionsER membraneCYTOSOLCTR1inactiveCTR1active kinase inactive ethylene receptorethylene polyubiquitinhiEIN3EIN3degradation in proteasomesDNADNAWhich statements provide the most direct evidence that the ethylene gas signalling mechanism functions to mediate gene expression?1In the absence of ethylene, active CTR1 stimulates the ubiquitination and degradation in proteasomes of EIN3.

2In the absence of ethylene, the active ethylene receptors halt transcription of ethylene-responsive genes through degradation of EIN3. 3In the presence of ethylene, its binding inactivates the receptor, altering their conformation so that they no longer activate CTR1. 4In the presence of ethylene, the EIN3 protein does not undergo selective degradation and can now activate the transcription of the large number of ethylene-responsive genes. A1 and 2 B2 and 3C2 and 4D3 and 42018 / H2 / AJC PRELIM / P1 Q244What is the main purpose of the second messengers in signal transduction pathways?AThey allow for long distance signalling between cells by being activated when they bind to extracellular molecules.BThey amplify the signal without involving protein kinase cascade. CThey can always cross the membranes of the organelles to initiate cellular processes.DThey relay a signal from the plasma membrane to the cytoplasm by sudden increase of their cytosolic concentration.

2018 / H2 / DHS PRELIM / P1 Q125One action of the hormone glucagon is to cause the activation of adenylyl cyclase in liver cells. Adenylyl cyclase is an enzyme that converts ATP into the messenger molecule cyclic AMP (cAMP), the presence of which triggers a cascade of events within the cell that leads to the breakdown of glycogen and the subsequent release of glucose into the blood stream. This pathway is summarised below.cAMP + PPiAdenylyl cyclaseactivatesGlucagoATPIncreased glycogen breakdown and release of glucose intothebloodstreamWhen glucagon is removed, adenylyl cyclase becomes inactive again and ceases to convert ATP to cAMP. The enzyme phosphodiesterase converts cAMP into AMP. The following table summarises an experiment measuring glucose release by liver cell cultures under various conditions.CultureCondition(s)Observation(s)1no addition of glucagon and caffeineminimal glucose release2glucagon added and later removedglucose released into media;rapid reduction in release after glucagon removed3caffeine addedminimal glucose release4glucagon and caffeine added;glucagon was then removed but caffeine maintainedglucose released into media;slow reduction in release after glucagon removedBased on these observations, which of the following statement is most likely to be true?ACaffeine stimulates synthesis of cAMP.BCaffeine prevents glucagon breakdown. CCaffeine inhibits the action of phosphodiesterase.DCaffeine binds the active site of adenylyl cyclase.

2018 / H2 / EJC PRELIM / P1 Q276The β-adrenergic receptor on muscle cells is a G-protein coupled receptor. Details of the cell signalling pathway in the presence of adrenalin is illustrated in the diagram below. Which of the following is correct?AInactivation of G protein occurs when GTP is displaced by GDP.BSignal amplification occurs at the step where G protein activates adenylyl cyclase.CDuring signal transduction, PKA can phosphorylate more than one type of molecule to activate them.DMuscle cells have decreased rate of glycogenesis and increased rates of glycolysis in the presence of adrenalin.

2018 / H2 / IJC PRELIM / P1 Q247The diagram shows an example of cell signalling. Which processes are shown on the diagram?PQRAamplificationligand-receptor interactionphosphorylationBligand-receptor interactionamplificationphosphorylationCtransductionphosphorylationamplificationDligand-receptor interactiontransductionamplification2018 / H2 / JJC PRELIM / P1 Q238What is the correct sequence of events in a cell in response to insulin?AHormone binding to receptor  dimerisation of polypeptides  cross phosphorylation  activation of insulin response protein  activation of glycogen phosphorylaseBHormone binding to receptor  dimerisation of polypeptides  cross phosphorylation  activation of insulin response protein  activation of glycogen synthaseCHormone binding to receptor  cross phosphorylation  dimerisation of polypeptides  activation of protein kinases  activation of glycogen phosphorylase

DHormone binding to receptor  cross phosphorylation  dimerisation of polypeptides  activation of insulin response protein  activation of glycogen synthase2018 / H2 / MJC PRELIM / P1 Q22QUESTION 9Which of the following correctly describes the function of second messengers in signal transduction pathway? AThey relay the signal from the outside to the inside of the cell.BThey serve as transcription factors to activate the transcription process.CThey amplify the signal by phosphorylating other proteins.DThey bind to and alter the conformation of other effector proteins.2018 / H2 / NJC PRELIM / P1 Q2610Which enzyme is not involved in the regulation of signal transduction pathways?AGTPaseBkinaseCphosphataseDphosphorylase2018 / H2 / ACJC PRELIM / P1 Q27 11The diagram shows part of a cell signalling pathway.

Which of the following correctly describes the numbered steps in the cell signalling pathway?1A heterotrimeric G-protein is associated with