What determines the trafficking pathway of proteins destined for different cellular compartments?

The trafficking pathway of proteins destined for different cellular compartments is determined by targeting signals within the polypeptides. These signals, often in the form of short peptide sequences, act as signposts that specify where a protein should go within the cell. For example, proteins destined for the nucleus typically contain nuclear localization signals, while those directed to the endoplasmic reticulum may have signal peptides that direct their synthesis on ribosomes at the ER surface.

These targeting signals are crucial because they are recognized by the cellular machinery responsible for protein transport, allowing proper sorting and delivery to ensure that proteins are localized correctly to carry out their functions. This specificity in signaling is essential for maintaining cellular organization and efficient functioning.

While receptor proteins, protein size, and the type of cell can impact protein trafficking in specific contexts, they are not the fundamental determinants of the pathways themselves. The inherent signaling within the protein sequences is the key element guiding their destination.