Cells can have two kinds of endoplasmic reticulum (ER): smooth ER, which has no
ribosomes, and rough ER, which has ribosomes embedded in its membrane. What
would happen if the rough endoplasmic reticulum in the cell of an organism lost all
of its ribosomes?
A. ATP production in the cell would stop.
B. Protein production in the organism would stop.
C. Storage of proteins within the cell would increase.
D. Proteins would no longer be exported from the cell.
The Correct Answer and Explanation is:
The correct answer is D. Proteins would no longer be exported from the cell.
Explanation:
The rough endoplasmic reticulum (rough ER) is involved in the synthesis and modification of proteins. Its key characteristic is the presence of ribosomes on its cytoplasmic surface. These ribosomes are responsible for translating messenger RNA (mRNA) into proteins. The rough ER provides a site for the folding and modification of these proteins, and it serves as a network that transports them within the cell.
If the rough ER were to lose all of its ribosomes, it would no longer be able to carry out protein synthesis. The ribosomes are critical for the translation process, where mRNA is used to build proteins. Without ribosomes, no new proteins could be made by the rough ER, disrupting cellular functions dependent on protein production.
In terms of protein export, many proteins that are synthesized on the rough ER are destined for secretion outside the cell or for integration into the cell membrane. Once synthesized and folded, these proteins are packaged into vesicles and transported to the Golgi apparatus for further processing and eventual export from the cell. Without ribosomes on the rough ER, the cell would fail to produce the proteins needed for these processes. Thus, proteins would no longer be exported from the cell, making answer choice D correct.
- Option A (ATP production) is incorrect because ATP production primarily occurs in the mitochondria, not the rough ER.
- Option B (Protein production) is partially correct but misleading in this context. Protein production in the organism would not entirely stop because other cell types might still have the ability to synthesize proteins through different mechanisms (e.g., in the cytoplasm), but export and processing of proteins in cells with a non-functional rough ER would be compromised.
- Option C (Storage of proteins) is not correct because the smooth ER is involved in storage of lipids and other molecules, not proteins. Proteins, in general, would not be stored in the rough ER without ribosomes for synthesis.
Therefore, the primary effect of losing ribosomes from the rough ER would be the inability to export proteins, which is reflected in option D.