In what structure are proteins produced?

Proteins are produced in the ribosome, which is a cellular structure specifically designed for protein synthesis. Ribosomes can be found in both prokaryotic and eukaryotic cells, functioning as the site where messenger RNA (mRNA) is translated into amino acid sequences, forming proteins. During this process, transfer RNA (tRNA) molecules bring amino acids to the ribosome, where they are linked together in the order specified by the mRNA, ultimately resulting in the formation of a polypeptide chain that folds into a functional protein.

While the endoplasmic reticulum and mitochondria play important roles in the cell, they do not directly produce proteins in the way ribosomes do. The endoplasmic reticulum functions in processing and modifying proteins after they are synthesized in the ribosome and is involved in lipid synthesis as well. The mitochondria are primarily involved in energy production and metabolic processes, rather than in the synthesis of proteins. The nucleus houses the genetic material and is where transcription of DNA into mRNA occurs, but the actual assembly of proteins takes place in the ribosomes. Thus, the ribosome is the correct answer as the main structure responsible for protein synthesis.