Final answer:
Proteins must be unfolded to cross the membranes of the mitochondria and the nucleus. Through collaboration of the endomembrane system, proteins are synthesized, modified, and transported within the cell. Mitochondria function as cellular power plants and is supported by the roles of vesicles and vacuoles.
Step-by-step explanation:
Proteins must be unfolded to cross the membranes of the mitochondria and the nucleus. When proteins are synthesized on ribosomes attached to the rough endoplasmic reticulum (RER), they enter into the RER lumen where they start folding into their three-dimensional structures. Proteins that are destined for the mitochondria or nucleus, however, often need to cross membranes where sizes of pores and transport mechanisms require them to be unfolded or partially unfolded. For example, the mitochondrial matrix has a double membrane, and proteins crossing into it typically do so in an unfolded state through mitochondrial pores.
The endomembrane system, which includes the ER, nucleus, and Golgi apparatus, works collaboratively to ensure that proteins are properly synthesized, folded, modified, and then shipped to their correct destinations. The RER is where ribosomes produce and deposit proteins into the lumen, which may then be modified and transported to the Golgi apparatus for further processing and sorting. These proteins are carried in vesicles, and once they are processed and packaged by the Golgi apparatus, they can be sent to various places within the cell or secreted outside the cell.
Mitochondria are referred to as the power plants of the cell because they generate most of the cell's supply of adenosine triphosphate (ATP), which is used as a source of chemical energy. Lastly, vesicles and vacuoles have roles in storage, transport, and waste disposal within the cell.