adrenaline activated a subunit of stimulatory G protein (G) 6. (2pts each) When
ID: 267590 • Letter: A
Question
adrenaline activated a subunit of stimulatory G protein (G) 6. (2pts each) When adrenaline binds to adrenergic receptors on the surface of a muscle cell, it activates a signaling pathway which ultimately releases glucose The figure to the right describes steps in this signaling pathway. Please circle whether you would predict the following mutant cell lines would have increased or decreased downstream signaling through this pathway CYTOSOL activated GPCR (adrenergic receptor) activated adenylyl cyclase A. Cells that lack adenylyl cyclase nactive PKA cyclic AMP increasedI decreased AMP B. Cells that lack the GPCR Downstream responses increasedI decreased C. Cells that express a constitutively active PKA increasedI decreased D. Cells that have a G protein a-subunit that cannot release GDP increasedI decreasedExplanation / Answer
A, decresed downstream signalling.
The sinalling pathway needs activation of adenyl cyclase by G protein. When activated, adenylyl cyclase converts a large number of ATP molecules into signaling molecules, called cyclic AMP which is needed for further signalling. Therefore, in the absence of adenyl cyclase the downstream signalling will be decreased.
B. decresed downstream signalling.
The first step in adrenaline signaling is the binding of adrenaline to the GPCR(G-protein coupled receptor) on the cell surface. It triggers the receptor to change shape, converting the receptor to its active. This step is required for carrying out the downstram signalling and hence lack of GPCR will decrease the downstream signalling.
C. increased downstream signalling.
The cAMP molecules produced by adenylyl cyclase continue the signaling cascade by binding to called protein kinase A. This binding triggers protein kinase A to separate into subunits, two of which are catalytically active. Active PKA is needed for further downstram signalling. Hence a mutant which constituitively express active PKA will have increased downstream signalling.
D. decreased downstream signalling.
The activated GPCR triggers a cascade of events within the cell, beginning with the activation of a G protein. The G protein binds to the activated receptor, the alpha subunit releases GDP, and it takes up a molecule of GTP. Hence mutant which in which G protein alpha subunit cannot release GDP will have decreased downstream signalling.
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