The cell organelle on which protein molecules are manufactured is the ribosome.

Here's why:

* Ribosomes are the protein factories of the cell. They read the genetic code carried by messenger RNA (mRNA) and use it to assemble amino acids into protein chains.

* Ribosomes are found in both prokaryotic and eukaryotic cells. They can be free-floating in the cytoplasm or attached to the endoplasmic reticulum.

* The process of protein synthesis is called translation. This occurs on the ribosome, where the mRNA sequence is translated into the amino acid sequence of a protein.

Let me know if you have any more questions about ribosomes or protein synthesis!