Ribosomissa

Ribosome is a large and complex molecular machine responsible for translating genetic information encoded in messenger RNA into polypeptide chains. It is composed of ribosomal RNA and ribosomal proteins and exists in two major subunits that come together during protein synthesis. In bacteria and archaea, the small subunit is 30S and the large subunit is 50S, forming a 70S ribosome. In eukaryotes, the equivalents are 40S and 60S, forming an 80S ribosome. Mitochondria and chloroplasts retain their own ribosomes, which resemble bacterial 70S ribosomes.

Ribosomes reside free in the cytosol or bound to membranes such as the endoplasmic reticulum in eukaryotic cells. Their primary function is to translate mRNA codons into amino acids carried by transfer RNAs, assembling them into a polypeptide according to the genetic code. The translation process comprises initiation, elongation, and termination, driven by various initiation, elongation, and release factors. The ribosome’s catalytic activity, peptidyl transferase, is performed by the large subunit's rRNA.

In structure, a ribosome has three binding sites for tRNA: A, P, and E. The active site forms primarily by rRNA, reflecting the ribosome’s status as a ribozyme. Ribosome biogenesis begins in the nucleus (in eukaryotes) with rRNA transcription and processing, followed by assembly with ribosomal proteins in the nucleolus and cytoplasm. Bacterial ribosomes are assembled in the cytoplasm.

Ribosomes are a major antibiotic target; many drugs disrupt bacterial ribosome function to inhibit protein synthesis. In Finnish, ribosome is ribosomi, and ribosomissa is the locative form meaning "in the ribosome."