|RIBOSOME(S)... ribonucleo-protein particles are supra-meolcular complexes made of 3 RNA single stranded pieces and a mix of 30 to 40 ribosomal proteins. These RNA's & polypeptides will self-assemble into a functional unit (roughly spherical - diameter 20nm) that is site of new protein sysnthesis in cells, translating mRNA into amino acid sequences. Ribosomes often aggregate to form structures known as "polysomes".
Eukaryotic ribosomes (80s) have 2 parts: a large subunit (60s) of 3 RNA's (28s/5s/5.8s) & 49 proteins, & a small subunit (40s) of 33 proteins & 1 RNA (18s). Prokaryotes have a smaller size (70s) than eukaryotic ribosomes. also with 2 subunits [large: (50s) 2 RNAs (23s/5s) & 33 proteins] & [small: (30s) 1 RNA (16s) & 21 proteins].
Ribosomes read mRNA's & have 3 sites for binding amino acids: an A site where the new amino acid is accepted, a P site where the growing polypeptide is held, & an E site where the tRNA's are released.
Eucaryotic ribosomes may be free in the cytoplasm or bound to an internal membrane structure, as the R.E.R or attached to a mRNA in a polysome. Eucaryotes also have small 70S ribosomes (procaryotic-size) in their mitochondria & chloroplasts. In fact it is thought that mitochondrion & chloroplasts mat have originated from bacteria.