Cells receive an array of signals that tell them what to do. Cells receive signals to survive, grow, divide, or differentiate, and if a cell receives no signals, it will undergo apoptosis and die. Cancer cells dont need survival signals, and this is why they continue to survive even when no signals are being received. Signals are typically small molecules or proteins. Hydrophobic signals, such as hormones, will enter the cell across the membrane and attach to receptors in the cell. On the other hand, hydrophilic signals cannot get inside of the cell and will bind to receptors on the cell surface. The same signal can be received by the same receptor, but depending on the cell type, the signal may cause different outcomes in the cell. For example, acetylcholine is a common signal, but when it binds to the same receptor on a different cell, different downstream proteins result. Signals usually set off signal cascades in which the message is amplified. Any time there are enzymes and multiple steps incolced in the transduction cascade, the signal can be amplified. This amplification of signals makes crosstalk more plausible. Crosstalk is when pathways intersect, affecting one another. The more steps in the pathway, the more opportunities for crosstalk. And the only way to completely stop the communication of a signal is to eliminate the last step of the pathway.
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