Which cellular structure is the primary site of protein synthesis?

Protein synthesis primarily occurs at ribosomes, which are complex molecular machines made of ribosomal RNA and proteins. These structures can be found free-floating in the cytoplasm or attached to the endoplasmic reticulum, forming what is known as the rough endoplasmic reticulum. Ribosomes read the sequence of messenger RNA (mRNA), which is transcribed from DNA in the nucleus, and translate this information into amino acids, assembling them into polypeptide chains that ultimately fold into functional proteins.

The role of ribosomes in translating the genetic code into proteins is vital for virtually all cellular functions and processes, making them essential for life. While other cellular structures, such as the nucleus and endoplasmic reticulum, play important roles in the processes preceding protein synthesis—like gene expression and post-translational modification—ribosomes directly carry out the final steps of assembling proteins. Mitochondria, while crucial for energy production, are not involved in the process of protein synthesis.