activation of proteins eg. many enzymes are activated by being phosphorylated - often involves cyclic AMP as a second messenger
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Where is cyclic AMP (cAMP) derived from?
adenosine triphosphate (ATP)
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How does cAMP activate proteins?
by altering their tertiary structure via the addition of a phosphate group.
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First step:
A signalling molecule, such as the hormone glucagon, binds to a receptor on the plasma membrane of the target cell.
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Second step:
This activates a transmembrane protein which then activates the G protein.
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Third step:
The activated G-protein activates adenyl cyclase enzymes.
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Fourth step:
Activated adenyl cyclase enzymes catalyse the formation of many molecules of cAMP from ATP.
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Fifth step:
cAMP activates PKA (protein kinase A)
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Sixth step:
Activated PKA catalyses the phosphorylation of various proteins, hydrolysing ATP in the process.This phosphorylation activates many enzymes in the cytoplasm, e.g. those that convert glycogen to glucose.
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Seventh step:
PKA may phosphorylate another protein (e.g. CREB - cAMP Response Element Binding)
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Eighth step:
This then enters the nucleus and acts as a transcription factor, to regulate transcription.
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