Question

Describe intracellular events that occur upon activation of the three main subtypes (based on second messengers) of G protein-coupled receptors versus steroid receptors.

Answer 1

There are three types of G_{​​​​​​s}, G_{​​​​​​i}, G_{​​​​​​q ^​​.}​​. When the second messanger comes and bind to the receptors the alpha subunit gets released from the beta and gamma subunit and the GDP is exchanged by GTP and thus it becomes activated. Gs stimulates adenylate cyclase which converts AMP to cyclic AMP which then changes different cellular responses. Gi inhibits adenylate cyclase. While Gq activates PLC which Activates two other second messangers IP3 and DAG which changes the intracellular calcium levels by releasing it from ER and also activates a kinase PKC which then activates other proteins and cause intracellular signalling.

The receptor in case of sterioid hormones remain in the cytosol instead of the plasma membrane. Steroid hormones being lipophilic enters the cell and interact with the receptor im the cytosol. The hormone receptor complex then travels to the nucleus where they interact with hormone response elements and causes the transcription of several genes while the receptor gets recycled back to the cytosol.