Which of the following is a function of the rough endoplasmic reticulum (ER) in the process of protein secretion?

• A. Synthesis of proteins destined for secretion
• B. Detoxification of drugs and poisons
• C. Synthesis of lipids for membrane formation
• D. Storage of calcium ions

Answer: (A)

Verified step by step guidance

1. Understand the structure of the rough endoplasmic reticulum (ER): It is studded with ribosomes on its cytoplasmic surface, which gives it a 'rough' appearance under a microscope.
2. Recognize the primary function of the rough ER: The ribosomes attached to the rough ER are sites for protein synthesis, specifically for proteins that are to be secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle.
3. Differentiate between the functions of the rough ER and the smooth ER: The smooth ER is involved in lipid synthesis, detoxification of drugs and poisons, and storage of calcium ions, which are not functions of the rough ER.
4. Identify the role of ribosomes in protein synthesis: Ribosomes on the rough ER translate mRNA into polypeptide chains, which are then folded and modified into functional proteins within the ER lumen.
5. Conclude that the synthesis of proteins destined for secretion is the specific function of the rough ER, distinguishing it from other cellular processes like detoxification or lipid synthesis, which are associated with the smooth ER.