The organelle that functions primarily in the synthesis of long chains of amino acids is the ribosome.

Here's why:

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

* Amino acids are the building blocks of proteins, and ribosomes are responsible for linking them together in the correct sequence, as determined by the mRNA instructions.

While other organelles like the endoplasmic reticulum and Golgi apparatus are involved in protein modification and transport, the ribosome is the key player in the initial synthesis of the protein chain.