1. In most cells, the amounts of G-alpha and G-beta-gamma subunits are closely m
ID: 205326 • Letter: 1
Question
1. In most cells, the amounts of G-alpha and G-beta-gamma subunits are closely matched. What effect might you expect if you were able to highly overexpress G protein beta and gamma subunits in the cell? Propose a mechanism whereby the cell normally keeps the amounts of different subunits in a balance.
2. What properties of nuclear receptors make them particularly well suited for regulating cellular lipid metabolism? In what way is this regulatory role similar and different from their role as receptors for extracellular signals?
Explanation / Answer
1.If you were able to highly overexpress G protein beta and gamma subunits in the cell,then that could lead to downstream signal even in the absence of activation of receptor by its ligand or receptor-mediated stimulation.G beta gamma subunits are able to activate some of the downstream effectors on their own, and therefore GDP would dissociate from the free G alpha subunits leading to GTP binding if most of the time passes and there is no binding to subunits. So, it is important that a mechanism should operate that can maintain the balance of the subunits within the cells.One of the mechanisms could be that unbound , , or subunits might be destructed by the ubiquitin proteasome system.Other mechanism could be transcriptional control in such as way that active signaling by free or subunits leads to negative feed back that could result in an decrease of the transcription of the genes that encode these subunits.
2.Nuclear receptors have two properties are well suited for regulating cellular lipid metabolism : 1)they bind specifically to different hydrophobic compounds and 2) they are involved in direct control of the transcription of target genes on binding of ligand. Thus nuclear receptors can sense the levels of different lipids and their metabolite as therefore can adjust the transcription of the genes that regulate those lipid synthesis accordingly. The difference between this role and the signaling role of nuclear receptors is specifically based on what the source of the ligand is i.e in case of lipid metabolism, the source of the lipid is internal while as a typical signaling role, the source of ligand is the outside of the cell environment like steroid hormones.
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