Recap Of Insulin Signaling in Glucose Metabolism - Video Tutorials & Practice Problems
On a tight schedule?
Get a 10 bullets summary of the topic
1
concept
Recap Of Insulin Signaling in Glucose Metabolism
Video duration:
7m
Play a video:
Video transcript
Alright. So here in this video, we're going to do a recap or a review of insulin signaling on glucose metabolism. And so we're not going to cover anything new in this video that we haven't already covered in our previous lesson videos. And so if you're feeling really, really good about insulin signaling on glucose metabolism, then feel free to skip this entire video if you'd like because, again, there's nothing new in this video that we haven't already covered. However, if you're struggling with this even just a little bit, then stick around because a review like this one could be really, really helpful everything that we talked about in our previous lesson videos regarding insulin signaling on glucose metabolism. And so if we start over here in the top left, of course, the 51 amino acid residue peptide, insulin, is going to act as the hormone or the ligand here in this situation. And, of course, insulin is going to bind to the insulin receptor, which we're showing down below right here. And the insulin receptor is a receptor Tyrosine Kinase or an RTK. And, of course, it has this, these 2 alpha subunits here that will bind the insulin receptor, and then it also has these 2 transmembrane beta subunits that the cytoplasmic tyrosine kinase domains. And they will autophosphorylate each other on tyrosine residues which is why we have the y's here, which is the one letter amino acid code for tyrosines. And so we end up getting these phosphorylated tyrosine residues on the insulin receptor. And that fully activates the insulin receptor so that it can actually target its substrates, which are the insulin receptor substrates or IRS 1 here, for example. And so when the insulin receptor targets IRS 1 as its substrate, it will actually phosphorylate IRS 1 on tyrosine residues. And so here we have the phosphorylated version of IRS 1. And that activates IRS 1 so that it can act as an adapter protein, which recall is just an a protein that lacks enzymatic activity and instead bridges other proteins together to activate them. And so this other protein that we see over here, p I three k or phosphoenosetide 3 kinase, has what's known as an SH 2 domain, and the SH 2 domain, recall, will bind specifically to phosphorylated Tyrosine Residues here on the IRS 1. And so when the SH 2 domain of PI 3 k binds to the phosphorylated Tyrosine Residues on IRS 1, that actually activates PI3K. And, again, PI 3 k is a kinase, so we know that it's going to phosphorylate its substrate. And its substrate is actually PIP 2 over here, And when it phosphorylates PIP 2, it converts it into PIP 3, which has one additional phosphate group on it. Then PIP 3 is still associated with the cytoplasmic side of this membrane, and so it can only laterally diffuse within the membrane. And so PIP 3 is going to laterally diffuse and associate itself with protein kinase b or pkb, and it will also laterally diffuse and associate itself with PDK 1 or, PIP dependent kinase 1. And so both p k b and p d k 1 are also kinases themselves. Now when PIP dependent kinase 1 binds to PIP 3, it actually activates pvk1. And so it's, again, a kinase, so it's going to phosphorylate its substrate, and its substrate is actually pkb. And so p, pdk 1, will phosphorylate pKb as we see here, using the ATP as the, phosphorylation source. And so you can see now we have the phosphorylated PKB, which fully activates PKB. And the fully activated PKB, remember, is a protein kinase, protein kinase b to be specific. And so it will also phosphorylate specific target proteins. And so, PKB will phosphorylate specific target proteins that we did not talk about in our previous lesson videos, but those specific target proteins that it phosphorylates will lead to the vesicle fusion with the plasma membrane, and these vesicles contain the glucose transporter GLUT 4. And so that allows GLUT 4, glucose transporter, to be expressed in the plasma membrane. And GLUT 4 will transport glucose from the bloodstream and transport it down its concentration gradient so that glucose can come into the cell. And, also, PKB will also phosphorylate specific enzymes that affect glycogen synthesis. More specifically, PKB will actually phosphorylate and inactivate GSK, Glycogen Synthase Kinase, and it will phosphorylate GSK, so that it becomes inactive. And so the inactive GSK 3 will no longer be able to phosphorylate and inactivate Gs, which is glycogen synthase. And so when GSK 3 or GSK cannot inactivate GS, that allows GS to be active, glycogen synthase, which is an enzyme that synthesizes glycogen. And so it will act on the glucose, specifically this glucose over here that was brought into the cell, and it will convert this glucose into glycogen, maintaining the glucose concentration inside of the cell relatively low so that the glucose in our bloodstream, which is relatively high after eating a meal, is able to, be transported down its concentration gradient from the bloodstream into the cell, ultimately decreasing blood glucose concentration, which is really the primary effect here of insulin signaling on glucose metabolism, that, blood glucose concentration is ultimately decreased after eating a high glucose meal. And so this here concludes our recap of insulin signaling on glucose metabolism and we'll be able to get a little bit more practice as we move forward in our course. So I'll see you guys in our next video.
2
Problem
Problem
What kinase phosphorylates IRS-1 in the insulin signaling pathway?
A
IRS-1 auto-phosphorylates itself.
B
PI3 Kinase.
C
PDK1.
D
The insulin receptor.
E
PKB.
3
Problem
Problem
IRS-1 is an essential adaptor protein in the insulin signaling pathway. If IRS-1 was overexpressed in muscle cells, what effect would you expect to see on glycogen synthesis?
A
Protein kinase B would remain inactive, resulting in increased glycogen synthesis.
B
Protein kinase B would be overstimulated, resulting in increased glycogen synthesis.
C
Protein kinase B would remain inactive, resulting in decreased glycogen synthesis.
D
Protein kinase B would be overstimulated, resulting in decreased glycogen synthesis.