Michigan Test for Teacher Certification (MTTC) Secondary Integrated Science Practice test

Where are ribosomes synthesized and partially assembled?

1. Nucleus

2. Nucleolus

3. Endoplasmic Reticulum

4. Golgi Apparatus

The correct answer is: Nucleolus

Ribosomes are synthesized and partially assembled in the nucleolus, which is a dense region within the nucleus of a cell. The nucleolus is specifically responsible for the production of ribosomal RNA (rRNA) and the combination of rRNA with ribosomal proteins to form the subunits of ribosomes. Once this initial assembly is complete, the ribosomal subunits are then transported out of the nucleolus into the cytoplasm, where they further assemble to form functional ribosomes that play a critical role in protein synthesis. The nucleus contains the genetic material and is where rRNA genes are transcribed, but the actual synthesis and initial assembly of ribosomes take place specifically in the nucleolus. Other cellular structures such as the endoplasmic reticulum and Golgi apparatus have different functions; the endoplasmic reticulum is primarily involved in the synthesis and processing of proteins and lipids, while the Golgi apparatus is responsible for modifying, sorting, and packaging these products for transport. Hence, the identification of the nucleolus as the site of ribosome synthesis aligns perfectly with the cellular biology associated with ribosome formation.