asterixis
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cAMP dependent protein kinases are activated by which of the following mechanisms?
a. Association of the catalytic subunits to form active dimers on binding to cAMP.
b. Association of the catalytic subunits with the regulatory subunits that are bound to cAMP.
c. Binding of cAMP to the regulatory subunits, which releases the catalytic subunits.
d. Binding of cAMP to both the regulatory subunits and catalytic subunits.
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| robin082006
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C?
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| disha
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| asterixis
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I have no idea what the answer is either  . The only thing that I found was that when the signal binds to the Gs protein linked receptor, there is an exchange of GDP to GTP to become an active Gs protein. This allows the alpha s chain to dissociate from the beta s chain and gamma s chain. The alpha s chain stimulates adenylate cyclase to increase cAMP levels. cAMP then activates the protein kinase. So, I was thinking about b, the association of the catalytic subunits with the regulatory subunits that are bound to cAMP. I don't know, please help.
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| krsna
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why not D?the regulatory unit is Gs alpha and the catalytic unit is adenylate cyclase...
pls clarify
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| r_albayunen
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| asterixis
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I think you're right. The regulatory protein is the Gs alpha and the catalytic is the adenyl cyclase. I thought it was the other way around but I think adenyl cyclase accelerates the reaction. Thanks.
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| luabe
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Binding of cAMP to the regulatory subunits (R) of protein kinase A releases the active catalytic (C) subunits which mediate various cellular responses.
therefore, C is correct answer
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| guest007
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no doubt....... it is C.......went through harper...on this easy but complicated issue.....huhhh...wiping my sweat from forehead now. 
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| xwxf
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c
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| liwei
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In cell biology, cAMP-dependent protein kinase (cAPK), also known as protein kinase A (PKA, EC 2.7.1.37), refers to a family of enzymes whose activity is dependent on the level of cyclic AMP (cAMP) in the cell.
Each PKA is a holoenzyme that consists of two regulatory and two catalytic subunits. Under low levels of cAMP, the holoenzyme remains intact and is catalytically inactive. When the concentration of cAMP rises (e.g. activation of adenylate cyclases by certain G protein-coupled receptors, inhibition of phosphodiesterases which degrade cAMP),
"""cAMP binds to the two binding sites on the regulatory subunits, which then undergo a conformational change that releases the catalytic subunits. """
The free catalytic subunits can then catalyze the transfer of ATP terminal phosphates to protein substrates at serine, or threonine residues. This phosphorylation usually results in a change in activity of the substrate. Since PKAs are present in a variety of cells and act on different substrates, PKA and cAMP regulation are involved in many different pathways. In addition, the effects of PKA phosphylation are generally transient because protein phosphatases quickly dephosphorylate PKA targets
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| Addicudo
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c. Binding of cAMP to the regulatory subunits, which releases the catalytic subunits.
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