Which structure is responsible for protein synthesis in the cell?

Ribosomes are the cellular structures responsible for protein synthesis. They function as the site where the translation of messenger RNA (mRNA) into polypeptide chains occurs. During this process, ribosomes read the sequence of the mRNA and facilitate the assembly of amino acids into proteins, based on the genetic instructions encoded in the mRNA.

Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum, which helps in the processing and transport of proteins after they are synthesized. This close association with the endoplasmic reticulum further emphasizes their role in protein synthesis and modification.

Other structures mentioned play significant roles in cellular processes but do not directly perform protein synthesis. The Golgi apparatus is involved in the modification, sorting, and packaging of proteins for secretion or delivery to different cellular destinations. The nucleus contains the cell's genetic material and is the site of transcription, where DNA is copied into mRNA, but it does not directly participate in protein synthesis itself. The endoplasmic reticulum aids in the transport and maturation of proteins synthesized by ribosomes, especially the rough endoplasmic reticulum, which is studded with ribosomes, yet it is the ribosomes that carry out the actual synthesis.