Which organelle is primarily responsible for protein synthesis?

Ribosomes play a crucial role in protein synthesis, which is the process by which cells create proteins necessary for various functions. They are composed of ribosomal RNA and proteins, and they can be found either floating freely in the cytoplasm or attached to the endoplasmic reticulum (in eukaryotic cells), forming what is known as rough ER.

During protein synthesis, ribosomes translate messenger RNA (mRNA) sequences into polypeptide chains, assembling amino acids in the order specified by the mRNA. This process is fundamental for cellular function and growth since proteins serve as enzymes, structural components, and signaling molecules.

The other organelles mentioned have different primary functions. Mitochondria are mainly involved in energy production through the process of cellular respiration. The nucleus houses the cell's genetic material and is the site where transcription (the creation of mRNA from DNA) occurs, but it is not directly involved in the translation of mRNA into protein. The Golgi apparatus functions in modifying, sorting, and packaging proteins for secretion or delivery to other organelles, rather than actually synthesizing proteins.