Signal Transduction in Cells

Cells in our body are surrounded by a lipid membrane. The "water-loving" heads of the phospholipid molecules (blue) are directed towards the outer and inner surfaces of the membrane. Many proteins stretch through the entire membrane.
A first messenger (1), a molecule of adrenaline, binds to a specific adrenaline receptor (2), a discriminator. Thereby, the transducer (3), a G protein - composed of alpha-, beta- and gamma subunits - is activated.
This, in turn, stimulates the amplifier (4), adenylate cyclase, which produces (5) the second messenger, cyclic AMP, from (6) ATP (adenosine- triphosphate).
(7) A cascade of enzymatic reactions alters the behaviour of the cell and (8) via phosphorylation (9) glycogen is transformed to (10) glucose, which the cell uses to generate ATP.
Phosphorylation can also alter membrane proteins, for example, ion channels (11).

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