Question

The dynamic figure above demonstrates how the endoplasmic reticulum is comprised of a network of membrane tubules found throughout the cytosol of eukaryotic cells. The tubular network is dynamic with connections continually being formed and broken. Which of the following statements about the ER network is NOT true? Choose one:

A. The ER produces proteins that are sent to other organelles such as the Golgi, lysosome and plasma membranes.
B. The ER is dynamic so tubules can be formed where needed.
C. The ER is the most extensive membrane system in eukaryotic cells.
D. The ER produces proteins that are sent out of the ER to many areas of the cytosol.

Answer 1

The untrue statement about the ER network is: the ER produces proteins that are sent out of the ER to many areas of the cytosol. The Option D is correct.

The endoplasmic reticulum (ER) is a membrane-bound organelle within eukaryotic cells that plays a central role in the synthesis, folding and transport of proteins and lipids. It comes in two forms which are rough ER (studded with ribosomes) involved in protein synthesis and smooth ER (lacking ribosomes) primarily responsible for lipid metabolism and detoxification.

As the ER does produce proteins, these proteins are primarily sent to other organelles and locations within the cell rather than being sent out of the ER into the cytosol. In fact, the ER is responsible for synthesizing proteins that are destined for secretion or integration into various cell membranes, such as the plasma membrane, Golgi apparatus, and lysosomes, rather than releasing them directly into the cytosol.