ribósómum

The ribósómum, or ribosome, is a complex molecular machine found within all living cells, both prokaryotic and eukaryotic. It serves as the site of protein synthesis, facilitating the translation of messenger RNA (mRNA) sequences into polypeptide chains, which later fold into functional proteins. Ribosomes are composed of ribosomal RNA (rRNA) and numerous proteins, organized into two subunits that assemble during protein synthesis.

In prokaryotes, such as bacteria, ribosomes are typically 70S, consisting of a 50S large subunit and a 30S small subunit. In eukaryotes, including humans, ribosomes are larger, classified as 80S, with a 60S large subunit and a 40S small subunit. The numerical designation reflects the sedimentation coefficient, measured in Svedberg units, which indicates the size and density of the ribosome.

The ribosome operates through three main stages: initiation, elongation, and termination. During initiation, the small subunit binds to mRNA and assembles with the large subunit, forming a complete ribosome. Elongation involves the sequential addition of amino acids to the growing polypeptide chain, guided by transfer RNA (tRNA) molecules that match codons on the mRNA. Termination occurs when a stop codon is reached, signaling the release of the completed protein.

Ribosomes can be free-floating in the cytoplasm or attached to the endoplasmic reticulum, where they synthesize proteins destined for secretion or membrane insertion. The structure and function of ribosomes are highly conserved across species, reflecting their essential role in cellular function. Mutations or disruptions in ribosome function can lead to diseases or developmental disorders, underscoring their importance in biology.