Which part of the endoplasmic reticulum is responsible for membrane production?

The rough endoplasmic reticulum (Rough ER) plays a vital role in membrane production due to its structure and function. It is studded with ribosomes on its cytoplasmic surface, giving it a "rough" appearance. These ribosomes are the sites of protein synthesis. As proteins are synthesized within the Rough ER, they often become integral components of cellular membranes, including the plasma membrane and the membranes of organelles.

Additionally, the Rough ER is involved in the initial steps of forming both membrane proteins and secretory proteins. After they are synthesized, these proteins are processed and folded within the lumen of the Rough ER, where they can then be packaged into vesicles for transport to other parts of the cell, including the Golgi apparatus for further processing.

In contrast, while the smooth endoplasmic reticulum (Smooth ER) is primarily involved in lipid synthesis, detoxification, and calcium storage, it does not have the same role in the synthesis of membrane proteins as the Rough ER. The nucleus is responsible for storing the genetic material and initiating the process of transcription but does not directly produce membranes.

Thus, the Rough ER’s role in synthesizing membrane proteins and its involvement in membrane production clearly establish it as the correct answer.