Recap of Phosphoinositide Signaling - Online Tutor, Practice Problems & Exam Prep
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Problem
Problem
Appropriately match each of the following terms with their description on the right.
a) Primary messenger ______. 1. Generates two secondary messengers.
b) Secondary messenger ______. 2. Stimulated by cAMP.
c) G-protein coupled receptor ______. 3. Activates phospholipase C.
d) Protein Kinase A ______. 4. Message received by the cell.
e) Gαs ______. 5. Composed of 7 transmembrane alpha-helices.
f) Gαq ______. 6. Results in the re-association of G α and Gβγ.
g) GTPase activity ______. 7. Intracellular chemical message that relays a signal from ligand receptor.
h) Phospholipase C ______. 8. Activates adenylate cyclase.
i) Inositol triphosphate ______. 9. Activated by diacylglycerol and Ca 2+.
j) Protein Kinase C ______. 10. Activates a Ca 2+ channel.
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Problem Transcript
Alright. So here we have a practice problem that wants us to appropriately match each of the following terms over here on the left-hand side with their correct description over here on the right-hand side. And of course, there are many different ways that you can approach solving this problem. In this video, we're just going to go through one possible way. So we're going to start at the top here with the primary messenger. And we're looking for which of these descriptions best fits with the primary messenger. Now recall that the primary messenger is also referred to as the ligand. And we know that this is going to be an extracellular molecule and it's going to carry the initial message that's received by the cell. So the primary messenger is going to link with option 4 here which says "message received by the cell". So, we can put 4 here for primary messenger and move on to the next one, which says secondary messenger. Recall that the secondary messenger comes after the primary messenger. The secondary messenger is going to be an intracellular molecule. It's going to match up with option 7 which says, an "intracellular chemical message that relays a signal from the ligand receptor" so it comes after the primary messenger, after the ligand and relays the signal. So, we can say option 7 best fits with the secondary messenger. We can go ahead and cross off option 4 and option 7 as we go along. Now moving on, what we have is G Protein-Coupled Receptor or GPCRs. Recall that GPCRs are also sometimes referred to as 7 TMS proteins, 7 transmembrane segments proteins. That's because they are composed of 7 transmembrane alpha helices. So, GPCRs or 7 TMS proteins, match best with option 5, which says that they're composed of 7 transmembrane alpha helices. So we can put 5 here and cross off 5. Next what we have is Protein Kinase A or PKA, which we know is going to be a kinase found in the adenylate cyclase GPCR signaling pathway. PKA exists as an inactive heterotetramer prior to the secondary messenger cAMP binding to it. When cAMP binds to PKA, that allows for the activation of PKA. So, 2 here is best going to fit with protein kinase A. Next, we have Gαs, which is the alpha subunit of the stimulatory G protein. We talked about the stimulatory G protein in the adenylate cyclase GPCR signaling pathway. It's going to stimulate the effector enzyme adenylate cyclase. The best option that matches with this is option 8 which says that it activates adenylate cyclase, that effector enzyme in that pathway. So we can put 8 right here and cross 8 off our list. Now next we have Gαq, which is the alpha subunit of the G protein involved in the phosphoinositide GPCR signaling pathway or the PSP pathway. The effector enzyme in that pathway is going to be phospholipase C or PLC. So Gαq is going to be responsible for activating that effector enzyme phospholipase C or PLC. So, 3 is going to best match with this option, and we can cross off 3 from the list. Now moving on we have GTPase activity. Recall GTPase activity is where the G protein is capable of hydrolyzing the high energy and active GTP into the low energy and inactive GDP. That is a way to inactivate the G protein and turn off the G protein. After GTPase activity, we know that the alpha subunit that dissociated is going to be able to reassemble its original form with the beta-gamma subunits. So option 6 here, which says that it results in the reassociation of the alpha subunit of the G protein with the beta and gamma subunits of the G protein, will go here and we can cross off option 6. Next, what we have is Phospholipase C or PLC, which we already mentioned is the effector enzyme in the phosphoinositide GPCR signaling pathway or the PSP pathway. So, phospholipase C is going to catalyze a reaction where it cleaves the substrate PIP2 into 2 secondary messengers, DAG or diacylglycerol, and IP3 or inositol triphosphate. So phospholipase C generates 2 secondary messengers, again, which are DAG and IP3, inositol triphosphate. So, what we can say is that option 1 best fits here, and then we can cross off 1 from our list. So, next what we have is Inositol Triphosphate, which is really just a long name for IP3, which we just said is one of the products of the enzyme-catalyzed reaction that phospholipase C catalyzes. So IP3, recall, is a cytosolic secondary messenger, and it's going to diffuse through the cytoplasm and bind to calcium ion channels in the endoplasmic reticulum to activate or open those calcium ion channels. So, Inositol Triphosphate is going to best match with option 10 here which says it activates a calcium channel, specifically in the endoplasmic reticulum. But here we can put in 10 and cross off 10. And then, of course, last but not least, the only one we have left is 9. So Protein Kinase C or PKC, we know is a kinase found in the phosphoinositide GPCR signaling pathway, and it's going to be activated by diacyl glycerol or DAG, as well as, the calcium that's released when Inositol Triphosphate binds. So 9 here is the best match with this, and we can cross off 9 from our list. Really, these numbers that you see here in this particular order are the answers to this practice problem. That concludes this practice, so I'll see you guys in our next video.