80SRibosomen

80S ribosomes are the cytoplasmic ribosomes used by most eukaryotic cells to synthesize proteins. They have a sedimentation coefficient of about 80S and are composed of a small 40S subunit and a large 60S subunit. The small subunit contains the 18S ribosomal RNA, while the large subunit contains the 28S, 5.8S, and 5S ribosomal RNAs. In total, the eukaryotic cytosolic ribosome comprises roughly 80 distinct ribosomal proteins distributed between the two subunits.

Functionally, 80S ribosomes translate messenger RNA into polypeptides. The small subunit is responsible for decoding the codons of the mRNA, and the large subunit provides the peptidyl transferase activity that forms peptide bonds. Initiation factors recruit the ribosome to the start codon on the mRNA, elongation factors drive the sequential addition of amino acids, and termination factors release the completed polypeptide at a stop codon. In eukaryotic cells, ribosomes can be free in the cytosol or bound to the rough endoplasmic reticulum, where they synthesize secreted, membrane-bound, or soluble proteins destined for specific cellular compartments or for secretion.

Biogenesis begins in the nucleolus, where rRNA transcription and initial assembly occur, followed by maturation and export of ribosomal subunits to the cytoplasm for final assembly. Compared with bacterial 70S ribosomes, 80S ribosomes are larger and contain more proteins and expanded rRNA domains. Some eukaryote-specific antibiotics and inhibitors target 80S ribosomes, such as cycloheximide and anisomycin, which block eukaryotic translation. Mitochondria and chloroplasts possess their own, distinct ribosomes (typically 55S or 70S).