Which of the following types of proteins are synthesized by the rough ER?

• A. Secretory proteins
• B. Mitochondrial proteins
• C. Nuclear proteins
• D. Cytosolic proteins

Answer: (A)

Verified step by step guidance

1. Understand the function of the rough endoplasmic reticulum (ER). The rough ER is studded with ribosomes, which are the sites of protein synthesis. It is primarily involved in the synthesis of proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle.
2. Identify the types of proteins synthesized by the rough ER. Secretory proteins are synthesized by the rough ER. These proteins are destined to be secreted out of the cell or sent to the cell membrane.
3. Consider the location and function of mitochondrial, nuclear, and cytosolic proteins. Mitochondrial proteins are typically synthesized in the cytosol and imported into the mitochondria. Nuclear proteins are also synthesized in the cytosol and imported into the nucleus. Cytosolic proteins are synthesized in the cytosol and remain there.
4. Compare the synthesis locations of these proteins. Secretory proteins are synthesized by the rough ER, while mitochondrial, nuclear, and cytosolic proteins are synthesized in the cytosol.
5. Conclude that the rough ER is responsible for synthesizing secretory proteins, as these are the proteins that require processing and transport through the ER and Golgi apparatus before being secreted or incorporated into the cell membrane.