Which cellular structure is involved in the synthesis of proteins?

The ribosome is the cellular structure responsible for the synthesis of proteins. Ribosomes can be found free in the cytoplasm or attached to the endoplasmic reticulum, forming what is known as rough ER. They function by translating messenger RNA (mRNA) sequences into polypeptide chains, which then fold into functional proteins.

This process of protein synthesis involves reading the mRNA transcriptions that are created in the nucleus and translating them into amino acid sequences. Ribosomes facilitate this process by providing a site for tRNA molecules, which carry amino acids, to interact with the mRNA strand, ensuring that the correct amino acids are added in the appropriate order to form proteins.

While the nucleus is where mRNA transcription occurs, it is not directly involved in the synthesis of proteins. The endoplasmic reticulum plays a role in the modification and transport of proteins after synthesis, and mitochondria are primarily involved in energy production rather than protein synthesis. Thus, ribosomes are the key players in the actual assembly of proteins, making them the correct answer to the question.