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