Which part of the cell is primarily responsible for protein synthesis?

The ribosome is primarily responsible for protein synthesis within the cell. Ribosomes can be found floating freely in the cytoplasm or attached to the endoplasmic reticulum. Their main function is to translate messenger RNA (mRNA) into amino acid sequences, which ultimately fold into functional proteins. This process involves binding to the mRNA and catalyzing the assembly of amino acids into polypeptide chains based on the sequence of codons present in the mRNA.

While the nucleus does play a crucial role in the initial stages of protein synthesis by housing the DNA that encodes the genes and producing mRNA through transcription, it does not directly synthesize proteins. The Golgi apparatus is involved in modifying, sorting, and packaging proteins for secretion or for use within the cell, rather than synthesizing them. Lysosomes, on the other hand, are responsible for digestion and waste removal within the cell and do not participate in protein synthesis. Therefore, the ribosome is the correct answer, as it is the site where the actual synthesis of proteins occurs.