English: The diagram depicted above shows the signal transduction pathway of the bitter taste. Bitter taste has many different receptors and signal transduction pathways. Bitter indicates poison to animals. It is most similar to sweet. Object A is a taste bud, object B is one taste cell, and object C is a neuron attached to object B.

I. Part I is the reception of a molecule. 1. A bitter substance such as quinine, is consumed and binds to G Protein-coupled receptors. II. Part II is the transduction pathway 2. Gustducin, a G protein second messenger, is activated. 3. Phosphodiesterase, an enzyme, is then activated. 4. Cyclic nucleotide, cNMP, is used, lowering the concentration 5. Channels such as the K+, potassium, channels, close. III. Part III is the response of the taste cell. 6. This leads to increased levels of Ca+. 7. The neurotransmitters are activated.