It consists of rRNA and protein components. The proteins protect rRNA from degradation by enzymes and form a very specific shape. It is hours in eukaryotes. Before RNA is finished synthesizing, ribosomes attach to the part that was first synthesized in prokaryotes. There is a leader sequence at the 5' end before the coding region, and a trailer sequence after the last coding sequence at the 3' end.
Ribosomes attach at first coding region.
When it gets to the end of that coding region, the ribosome comes off. The ribosome attaches again at the next coding region. Ribosomes interact separately with each cistron. This is a mutation in cistron that effects the expression of another downstream cistron. Usually it is a nonsense mutation, one that inserts a stop codon.