Humber Admissions Practice Test

Which of the following is NOT a function of the rough endoplasmic reticulum?

1. Lipid synthesis

2. Protein synthesis

3. Transport of proteins

4. Assembly of ribosomes

The correct answer is: Lipid synthesis

The rough endoplasmic reticulum (RER) is primarily involved in the synthesis of proteins and their transport within the cell. It is studded with ribosomes, which synthesize proteins that are either secreted from the cell, incorporated into the cell's plasma membrane, or sent to an organelle. The RER also plays a crucial role in the transport of these newly synthesized proteins to other locations within the cell, such as the Golgi apparatus, for further processing and distribution. While the RER has some roles in the modification of lipids associated with these processes, lipid synthesis is not primarily the function of the rough endoplasmic reticulum. Instead, lipid synthesis occurs mainly in the smooth endoplasmic reticulum, which lacks ribosomes and is specialized for the production of lipids and metabolism. The assembly of ribosomes, on the other hand, takes place in the nucleolus, not the RER, although the ribosomes that assemble there may attach to the RER for protein synthesis. Understanding these distinctions highlights the specialized functions of different cellular structures.