Which identifies correctly how the G protein–linked receptors are similar?

Question

A) Their cytosolic domain has intrinsic enzyme activity.
B) Insulin is an example of the second messenger cAMP, which binds to an enzyme-linked receptor.
C) These linked receptors are involved in rapid synaptic signaling between cardiac electrical cells.
D) They have a ligand-binding extracellular receptor component, which causes changes that activate the G protein on the cytoplasmic side of the cell membrane.

Answer 1

Ans: D
Feedback:
Although there are differences among the G protein–linked receptors, all share a number of features. They all have a ligand-binding extracellular receptor component, which recognizes a specific ligand or first messenger. Upon ligand binding, they all undergo conformational changes that activate the G protein found on the cytoplasmic side of the cell membrane. Instead of having a cytosolic domain that associates with a G protein, enzyme-linked receptors have cytosolic domain either that has intrinsic enzyme activity or that associates directly with an enzyme. The binding of the hormone to a special transmembrane receptor results in activation of the enzyme adenylyl cyclase at the intracellular portion of the receptor. This enzyme then catalyzes the formation of the second messenger cAMP, which has multiple effects on cell function. Insulin, for example, acts by binding to an enzyme-linked receptor. Ion channel–linked receptors are involved in the rapid synaptic signaling between electrically excitable cells.