English: The diagram above depicts the signal transduction pathway of the sweet taste.

Object A is a taste bud, object B is one taste cell of the taste bud, and object C is the neuron attached to the taste cell. I. Part I shows the reception of a molecule. 1. Sugar, the first messenger, binds to a protein receptor on the cell membrane. II. Part II shows the transduction of the relay molecules. 2. G Protein-coupled receptors, second messengers, are activated. 3. G Proteins activate adenylate cyclase, an enzyme, which increases the cAMP concentration. Depolarization occurs. 4. The energy, from step 3, is given to activate the K+, potassium, protein channels. III. Part III shows the response of the taste cell. 5. Ca2+, calcium, protein channels is activated. 6. The increased Ca2+ concentration activates neurotransmitter vesicles.

7. The neuron connected to the taste bud is stimulated by the neurotransmitters.