What are membrane bound receptors?

Whats the role of membrane bound receptors? exam revision!?

• Answer:

  Membrane-bound receptors serve to recognize and combine with stimulatory or inhibitory substances delivered to the cell, and translate this recognition function into a biologic action. Most membrane-bound receptors are proteins associated with the cell membrane. They typically span across the membrane, and can transmit a signal from outside the cell to inside the cell. Outside the cell, a ligand, such as a hormone, binds to the receptor, which causes the receptor to change it's shape. The shape change is detected inside the cell, thus transmitting a signal from the outside to the inside of the cell. Inside the cell, other proteins interact with the receptor in its new shape and are either activated or inhibited, thus continuing the signal pathway. For example, G proteins, short for guanine nucleotide-binding proteins, are a family of proteins involved in second messenger cascades. G proteins are so called because they function as "molecular switches," alternating between an inactive guanosine diphosphate (GDP) and active guanosine triphosphate (GTP) bound state, ultimately going on to regulate downstream cell processes. Receptor-activated G proteins are bound to the inside surface of the cell membrane. When a ligand activates the G protein-coupled receptor, it induces a conformation change in the receptor (a change in shape) that allows the receptor to function as a guanine nucleotide exchange factor (GEF) that exchanges GTP in place of GDP on the Gα subunit. Gαs stimulates the production of cAMP from ATP. This is accomplished by direct stimulation of the membrane-associated enzyme adenylate cyclase. cAMP acts as a second messenger that goes on to interact with and activate protein kinase A (PKA). PKA can then phosphorylate a myriad of downstream targets.