The processing requirements include successful completion of: 1  The application process, which includes a background and polygraph examination, a medical examination, a physical fitness evaluation, and a written examination; 2  24-26 weeks of intensive Academy training.
The cell membrane, being exposed to the outside environment, is an important site of cell-cell communication. As such, a large variety of protein receptors and identification proteins, such as antigens, are present on the surface of the membrane.
1 Binding of the signal molecule to the receptor protein will activate intracellular signaling proteins that initiate a signaling cascade. 2  Target proteins: the conformations or other properties of the target proteins are altered when a signaling pathway is active and changes the behavior of the cell. protein-coupled receptors comprise a large protein family of transmembrane receptors. They are found only in eukaryotes. The ligands which bind and activate these receptors include: photosensitive compounds, odors, pheromones, hormones, and neurotransmitters.