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.
The presence of one signal can affect the response to another signal. This means the cell can have different responses depending on the combinations of signals received. What do receptors do when they receive a signal? A given receptor (generally a protein) is specific for a particular signal. If that signal shows up at the cell, the receptor will bind it and this binding causes the receptor, in turn, to generate a new signal within the cell. This is called the first step in signal transduction.