What might be the effect on liver function of a mutation in...

Key Concepts

cAMP Signaling

This concept involves the role of cyclic AMP as a critical second messenger in signal transduction. In liver cells, cAMP mediates responses to hormones like glucagon by activating protein kinase A, which then phosphorylates various downstream targets to regulate metabolism, particularly glycogenolysis and gluconeogenesis. Alterations in components of this pathway can significantly shift cellular responses and metabolic balance.

G Protein-Coupled Receptors (GPCRs)

GPCRs are membrane receptors that mediate the effects of many hormones, including glucagon, by activating heterotrimeric G proteins. When a ligand binds to the receptor, the associated G protein exchanges GDP for GTP, initiating a cascade that often leads to the production of cAMP. Mutations that affect GPCRs can disrupt this cascade, leading to impaired signal transduction and metabolic dysregulation in the liver.

Phosphorylase Kinase and Glycogenolysis

Phosphorylase kinase is an enzyme critical for the activation of glycogen phosphorylase, the enzyme responsible for breaking down glycogen into glucose. This step is essential for mobilizing stored energy, especially in liver tissue during fasting or stress. A loss-of-function mutation in phosphorylase kinase can lead to reduced glycogenolysis, thereby limiting the liver’s ability to release glucose into the bloodstream.

GTPase Activity in G Protein Signaling

The intrinsic GTPase activity of the G protein ? subunit is essential for turning off the signal transduction cascade. Once activated by GTP binding, the G protein will normally hydrolyze GTP to GDP, thus terminating the signal. A loss-of-function mutation in the GTPase active site can lead to prolonged activation of the signaling pathway, resulting in sustained cellular responses such as enhanced cAMP production, which may disrupt normal hepatic metabolic processes.

Transcript

00:01 Okay, in order to answer this question, let's talk about the pathway of the g -stimulatory protein, okay? if this is your cell, i'm going to have here a g -protein couple receptor, that is also called seven -pass receptor.

00:18 Normally, it is an intracellular part, it is attached to a g -protein but has an alpha subunit, a beta -subunit, a gamma subunit.

00:29 Normally when there is no ligand here, this alpha subjunit is bound to gdp.

00:34 It is going to be an inactive form.

00:37 But when a ligand binds here, then this gdp is going to be removed and it is going to bind to gtp.

00:45 Okay.

00:46 Once it binds to gtp, it's going to get active and it's going to detach from these two subunits.

00:53 It is going to activate the protein called adelanalyze cyclics.

00:56 This adenitalized cyclist is going to break down atp.

01:00 Into cyclic amp and the levels of secretingp are going to guise.

01:05 This cyclic amp is going to activate the protein kinase a and it is going to cause a correlation of ion channels or transcription factors or enzymes.

01:15 Okay, it's practically a biological response.

01:18 But this process shouldn't be turned on forever, okay? it has to be turned off at some point.

01:25 So in order to stop this increasing, increased levels of cyclical, amp, this alpha subjunit has an intrinsic gtp that is going to break down this gtp into gtp, and alpha sodium is going to bind gtp and hence it is going to become inactive, okay? but also there are other molecules like phosphoryesterase, okay, that is going to break down this cyclic amp into amp, and hence it is going to turn off all this process.

01:52 Let's go to the question.

01:53 It says, what might be the effect on liver function of a mutation in a gene that encores a cyclic amp phosphorus yesterday.

02:01 Also it says that assume in all cases that the mutation causes a lot of function of the gene product.

02:06 So we're going to have a lot of functions of cyclic an amp phosphory estrase.

02:12 Okay, so as the function of or the normal function of phosphoidsstories was to break down cyclic amp in turn of this process, then this function is not going to cure.

02:25 Okay, and the levels of cyclic amp are going to get me high.

02:28 So, question, a, the response or the answer is going to be that there are going to be cyclic, a high levels of cyclic amp and this pathway is going to remain active in the liver.

02:42 Okay, so the liver is going to remain in an active form.

02:46 Now let's go for question b.

02:48 It says a mutation in a gene encoding a glucagon receptor.

02:54 So normally the liver is the place where two main pathways occur...

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