Proteins embedded in the ER with their N terminus located in the ER lumen may po

Question

Proteins embedded in the ER with their N terminus located in the ER lumen may potentially be found in which of the following?

Embedded in the membrane of the Golgi apparatus with its N terminus facing the cytosol

Embedded in the plasma membrane with its N terminus facing the cytosol

Embedded in the plasma membrane with its N terminus facing the extracellular matrix

Embedded in the nuclear membrane with its N terminus facing the cytosol

Embedded in the nuclear membrane with its N terminus facing the inside the nucleus

Embedded in the membrane of the Golgi apparatus with its N terminus facing the cytosol

Embedded in the plasma membrane with its N terminus facing the cytosol

Embedded in the plasma membrane with its N terminus facing the extracellular matrix

Embedded in the nuclear membrane with its N terminus facing the cytosol

Embedded in the nuclear membrane with its N terminus facing the inside the nucleus

Explanation / Answer

Correct answer –c

Proteins embedded in the ER with their N terminus located in the ER lumen may potentially be found embedded in the plasma membrane with its N terminus facing the extracellular matrix.

The proteins synthesised in the ER are destined to be a part of ER membrane, plasma membrane or are secreted out of the cell (secretory proteins). In particular, the proteins that remain embedded in ER membrane are known to be targeted to the plasma membrane. However, the proteins synthesised in cytoplasm are either retained in the cytoplasm or are targeted to mitochondria, chloroplast, and nucleus. Hence, options a, d, and e are not possible.

The protein embedded in ER membrane with N terminal exposed to the lumen of ER is eventually glycosylated at N terminal in ER and golgi apparatus. This glycosylated region of the protein is exposed to the cell surface/ extracellular matrix. Hence, option b is not feasible. Therefore, the correct answer is c.

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