Final answer:
Eukaryotic cytoplasmic proteins are directed to their specific destinations by traffic signals and are not all intended to be in the cytoplasmic membrane. They are sorted immediately upon synthesis and routed for secretion, incorporation into membranes, or localization to organelles. Peripheral proteins can dissociate easily, while transmembrane proteins remain embedded due to their hydrophobic domains.
Step-by-step explanation:
The proteins synthesized in the eukaryotic cytoplasm are often directed to specific cellular destinations, not all are meant to reside within the cytoplasmic membrane itself. Proteins are encoded in the nucleus and translated in the cytosol. Many of these proteins contain oligopeptide traffic signals which dictate whether they will end up within the nucleus, incorporated into the plasma membrane, or directed to internal organelles like mitochondria or chloroplasts after their synthesis within the cytoplasm.
Furthermore, the mechanism of protein secretion and the endomembrane system play crucial roles in the sorting process. Proteins destined for secretion or residence within cell membranes are directed to their respective locations immediately upon synthesis through a series of cellular compartments, such as the rough endoplasmic reticulum and the Golgi apparatus, eventually being packaged into vesicles. Those meant for membrane insertion or organelle localization will never linger freely within the cytosol.
Peripheral proteins, while associated with membranes, are typically found only on one side and can dissociate more readily compared to transmembrane proteins, which remain embedded within the bilayer due to their hydrophobic domains. This distinct arrangement allows for the separation and specialization of cellular functions, contributing to the complexity of eukaryotic cells. Given their diverse functions and locations, the absence of abundant proteins in the cytoplasmic membrane is due in part to the cellular machinery that segregates proteins to the appropriate cellular locales.