Which organelle is primarily responsible for protein synthesis?

The ribosomes are primarily responsible for protein synthesis in the cell. They serve as the site where messenger RNA (mRNA) is translated into proteins. During this process, ribosomes read the sequence of the mRNA and assemble the corresponding amino acids into polypeptide chains to form proteins. This function is vital for cellular processes, as proteins play crucial roles in structure, function, and regulation of the body's tissues and organs.

While the endoplasmic reticulum (specifically the rough endoplasmic reticulum) is involved in the folding and processing of proteins synthesized by ribosomes, it does not itself create proteins. The nucleus contains the genetic material and is where transcription occurs, generating mRNA from DNA, but it does not directly synthesize proteins. Mitochondria are primarily involved in energy production through the process of cellular respiration and are not directly responsible for protein synthesis. Therefore, ribosomes are the key organelles that perform this essential function in the cell.