Which structure is primarily involved in protein synthesis by translating mRNA?

The ribosome is the cellular structure primarily responsible for protein synthesis by translating mRNA. During the process of translation, ribosomes read the sequence of the mRNA and coordinate the assembly of amino acids into a polypeptide chain, forming proteins. Ribosomes can be found free-floating in the cytoplasm or attached to the endoplasmic reticulum, where they play an essential role in synthesizing proteins based on the genetic information carried by mRNA.

The nucleus is not involved in the translation process; instead, it is the site where mRNA is transcribed from DNA. The endoplasmic reticulum, while it is involved in protein processing and transport, does not directly translate mRNA into proteins. Lysosomes are cellular organelles that focus on digestion and waste management and do not participate in protein synthesis at all. Therefore, the ribosome is accurately identified as the structure that directly translates mRNA into protein.