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Programmed cell death is important for normal physiological functioning, it is crucial in wound healing, development, differentiation and immune responses. However, unregulated cell death can lead to development of several diseases. Several forms of cell death include apoptosis, necrosis, and autophagy, which differ mainly in the cells morphological changes that accompany them, as well as the proteins involved in their activation and execution.

Structural proteins are involved in maintenance of cellular structures and are crucial in cell polarity, cell to cell communication, movement and migration, cell division and other functions requiring cell malleability. Structural differences among cell types are crucial for cells to perform their specialized functional roles. Structural proteins are fibrous proteins, and include keratins, actin, collagens, and tubulins among others.

Cells must transport proteins from the endoplasmic reticulum in the cytoplasm, where they are mostly synthesized, to the nucleus, plasma membrane or other sites where they will ultimately perform their functions, and they should recycle back membrane and extracellular components. Intracellular trafficking involves two major pathways, the exocytic pathway, which transports components from the inside to the outside of the cell, and the endocytic pathway which transports material from the outside to the inside of the cell. Integral membrane proteins and secreted proteins are transported to the cell surface via the exocytic pathway, in which they are carried from the endoplasmic reticulum, to the Golgi apparatus and through secretory vesicles which then fuse with the plasma membrane. On the other hand, some cell surface receptors, after activation and signaling, undergo endocytosis and transport to lysosomes for their degradation, in a series of vesicular bodies called endosomes.