Question

Which of the following about the endoplasmic reticulum (ER) is TRUE?

a. A special class of ribosomes embedded in the ER translates the proteins destined for
that organelle.
b. The ER membrane is contiguous with the Golgi membrane
c. Steroid hormones are synthesized on the rough ER.
d. Proteins to be delivered to the ER lumen are synthesized on smooth ER.
e. It is believed that the nuclear membrane and the ER have evolved through invagination of the plasma membrane.

Answer 1

The ER membrane is contiguous with the Golgi membrane. This continuity facilitates the seamless transfer of vesicles between the endoplasmic reticulum and the Golgi apparatus, crucial for the processing and transportation of cellular components. Thus the true statement is option B. The ER membrane is contiguous with the Golgi membrane.

Step-by-step explanation:

The endoplasmic reticulum (ER) is a complex organelle with distinct roles in cellular functions. Option (b) is true because the ER membrane is indeed contiguous with the Golgi membrane. This continuity allows for the smooth flow of vesicles containing proteins and lipids between these two organelles, facilitating the processing and transportation of molecules within the cell.

Unlike option (a), where proteins destined for the ER are synthesized on ribosomes embedded in the ER membrane, it's actually the rough ER that bears these ribosomes. The rough ER is studded with ribosomes on its cytoplasmic surface, involved in the synthesis of proteins that are either secreted from the cell or incorporated into the membranes.

Option (c) is incorrect because steroid hormones are synthesized in the smooth ER, not the rough ER. The smooth ER is responsible for lipid metabolism, including the synthesis of steroid hormones. Finally, option (d) is inaccurate as proteins destined for the ER lumen are synthesized on ribosomes attached to the rough ER, not the smooth ER. The rough ER's ribosomes play a crucial role in the translation of proteins targeted for the ER lumen.

In summary, understanding the functions and structural characteristics of the endoplasmic reticulum clarifies that option (b) is the true statement among the given choices.

Thus the true statement is option B. The ER membrane is contiguous with the Golgi membrane.

Answer 2

The ER and Golgi apparatus are part of the endomembrane system, and their membranes are connected, allowing for the transport of lipids and proteins between these organelles. The correct statement about the endoplasmic reticulum (ER) is (b) The ER membrane is contiguous with the Golgi membrane.

Step-by-step explanation:

The endoplasmic reticulum (ER) is a crucial cellular organelle involved in the synthesis, folding, modification, and transport of proteins and lipids. Option (b) asserts that the ER membrane is contiguous with the Golgi membrane, and this statement is accurate. The endomembrane system, comprising the ER, Golgi apparatus, vesicles, and lysosomes, functions cohesively in the processing and transportation of cellular materials.

This continuity between the ER and Golgi membranes is vital for the secretory pathway. Proteins synthesized in the rough ER (characterized by ribosomes on its surface) move through the ER membrane to the Golgi apparatus for further processing and sorting before reaching their final cellular destinations. This dynamic connection ensures the smooth flow of proteins and lipids within the cell.

Contrastingly, option (a) is incorrect as proteins destined for the ER are synthesized on the rough ER itself, not by a special class of ribosomes embedded in the ER. Options (c) and (d) are also incorrect; steroid hormones are synthesized in the smooth ER, and proteins destined for the ER lumen are synthesized on the rough ER, not the smooth ER.

In summary, understanding the spatial relationship between the ER and Golgi membranes provides insights into the intricate processes of cellular protein and lipid trafficking, highlighting the interconnectedness of cellular organelles within the endomembrane system.

The correct statement about the endoplasmic reticulum (ER) is (b) The ER membrane is contiguous with the Golgi membrane.