The organelle responsible for protein assembly or synthesis is the ribosome.

Here's why:

* Ribosomes are the cellular machinery that reads the genetic code from messenger RNA (mRNA) and uses it to link amino acids together in the correct order, creating a protein chain.

* This process is called translation.

* Ribosomes can be found free-floating in the cytoplasm or attached to the endoplasmic reticulum (ER).

Let me know if you'd like to learn more about ribosomes or protein synthesis!