Which structure in cells is associated with assembling proteins?

Ribosomes are the cellular structures primarily responsible for the assembly of proteins. They facilitate the translation of messenger RNA (mRNA) into a polypeptide chain, which ultimately folds into a functional protein. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, forming rough ER; this positioning plays a role in determining where proteins will be synthesized—either for use within the cell or for export outside the cell.

In contrast, the nucleus is the control center of the cell and is primarily involved in storing and transmitting genetic information, as well as regulating gene expression. Mitochondria are known as the powerhouses of the cell because they are responsible for producing energy in the form of ATP through cellular respiration. Chloroplasts, found in plant cells, are involved in photosynthesis, converting light energy into chemical energy. While these structures play critical roles in cellular function, they are not directly involved in the protein assembly process that ribosomes perform.