The small particle in a cell on which proteins are assembled, made of RNA and protein, is called a ribosome.

Here's a breakdown:

* Ribosomes are complex molecular machines found within all living cells.

* They are responsible for protein synthesis, the process of translating genetic information from messenger RNA (mRNA) into proteins.

* Ribosomes consist of two subunits: a large subunit and a small subunit.

* Both subunits are made up of ribosomal RNA (rRNA) and proteins.

* rRNA provides the structural framework for the ribosome and plays a crucial role in the decoding of mRNA.

* Ribosomal proteins help to stabilize the structure of the ribosome and facilitate its interactions with other molecules involved in protein synthesis.

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