Proteins 'know' where to go in a cell because of signal sequences, which guide them to specific compartments, and the three-dimensional structure they fold into after protein synthesis.
Proteins are essential molecules that perform numerous functions in organisms, and they 'know' where to go in the cell because of their structure and signal sequences. During and after protein synthesis, proteins fold into a specific three-dimensional structure, which is determined by their amino acid sequence. Some proteins also have signal sequences attached to them, acting like a 'train ticket' that directs the protein to a specific cellular compartment, whether it be the cytoplasm, cellular membranes, inside organelles, or extracellular fluids. These signal sequences are recognized by other cellular factors which assist in their transport. For example, a sequence at the amino end could direct a protein to the mitochondria or chloroplasts. Once at the destination, the signal sequences are usually clipped off. Meanwhile, integral membrane proteins utilize stop transfer sequences during their sorting and targeting.