AEMCA Practice Exam

Which structure is responsible for synthesizing proteins?

1. Mitochondria

2. Rough endoplasmic reticulum

3. Golgi apparatus

4. Smooth endoplasmic reticulum

The correct answer is: Rough endoplasmic reticulum

The rough endoplasmic reticulum (RER) is primarily responsible for synthesizing proteins, making it the correct choice. This structure is studded with ribosomes on its cytoplasmic surface, which gives it a "rough" appearance. Ribosomes are the molecular machines that translate messenger RNA (mRNA) into protein. As proteins are synthesized on the ribosomes, they are threaded into the lumen of the rough endoplasmic reticulum, where they undergo folding and modifications important for their function and stability. In contrast, other structures serve different critical roles. Mitochondria are primarily involved in energy production through cellular respiration, generating ATP that powers various cellular processes. The Golgi apparatus functions mainly in refining, sorting, and packaging proteins and lipids for secretion or delivery to various cellular destinations, rather than synthesizing them. The smooth endoplasmic reticulum, while also part of the endoplasmic reticulum network, is involved in lipid synthesis and detoxification processes, but lacks ribosomes and is not directly responsible for protein synthesis. Therefore, the role of the rough endoplasmic reticulum in protein synthesis sets it apart as the correct answer.