American Society for Clinical Pathology (ASCP) Histotechnologist Practice Test

What cell structure is often attached to the endoplasmic reticulum and serves as the site of protein synthesis?

1. Mitochondria

2. Nucleus

3. Ribosomes

4. Golgi apparatus

The correct answer is: Ribosomes

Ribosomes are the cell structures that are often attached to the endoplasmic reticulum and are crucial for protein synthesis. These small, round structures can exist freely within the cytoplasm or be bound to the rough endoplasmic reticulum (RER), which gives the RER its "rough" appearance. When ribosomes are attached to the RER, they translate messenger RNA (mRNA) into polypeptide chains, which will fold into functional proteins. The endoplasmic reticulum itself acts as a network for synthesizing and transporting these proteins, with the rough ER specifically involved in the production of proteins that will be secreted or incorporated into cell membranes. This relationship underscores the importance of ribosomes in the process of translating genetic information into functional biomolecules, thus playing a pivotal role in cellular function and expression. The other structures mentioned, while vital for cellular processes, do not serve as the site of protein synthesis in the same direct manner as ribosomes. Mitochondria are involved primarily in energy production, the nucleus houses genetic information, and the Golgi apparatus is essential for modifying and packaging proteins after they have been synthesized, rather than directly involved in their synthesis.