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The ribosome is a large and complex molecular machine that catalyzes the synthesis of proteins, referred to as translation. The ribosome selects aminoacylated transfer RNAs (tRNAs) based on the sequence of a protein-encoding messenger RNA (mRNA) and covalently links the amino acids into a polypeptide chain. Ribosomes from all organisms share a highly conserved catalytic center. However, the ribosomes of eukaryotes (animals, plants, fungi, and many unicellular organisms with a nucleus) are much larger than prokaryotic (bacterial and archaeal) ribosomes and subject to more complex regulation and biogenesis pathways.〔(【引用サイトリンク】title=Difference Between 70S Ribosomes and 80S Ribosomes, RNA, Micromolecules )〕〔(【引用サイトリンク】title=80S Ribosomes, Eukaryotic Ribosomes, Prokaryotic Ribosomes, Nucleic Acids, Sedimentation Coefficient )〕 Eukaryotic ribosomes are also known as 80S ribosomes, referring to their sedimentation coefficients in Svedberg units, because they sediment more slowly than the prokaryotic (70S) ribosomes. Eukaryotic ribosomes have two unequal subunits, designated small subunit (40S) and large subunit (60S) according to their sedimentation coefficients. Both subunits contain dozens of ribosomal proteins arranged on a scaffold composed of ribosomal RNA (rRNA). The small subunit monitors the complementarity between tRNA anticodon and mRNA, while the large subunit catalyzes peptide bond formation. ==Composition== Compared to their prokaryotic homologs, many of the eukaryotic ribosomal proteins are enlarged by insertions or extensions to the conserved core. Furthermore, several additional proteins are found in the small and large subunits of eukaryotic ribosomes, which do not have prokaryotic homologs. The 40S subunit contains a 18S ribosomal RNA (abbreviated 18S rRNA), which is homologous to the prokaryotic 16S rRNA. The 60S subunit contains a 26S rRNA that is homologous to the prokaryotic 23S ribosomal RNA. In addition, it contains a 5.8S rRNA that corresponds to the 5' end of the 23S rRNA, and a short 5S rRNA. Both 18S and 26S have multiple insertions to the core rRNA fold of their prokaryotic counterparts, which are called expansion segments. For a detailed list of proteins, including archaeal and bacterial homologs please refer to the separate articles on the 40S and 60S subunits. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Eukaryotic ribosome (80S)」の詳細全文を読む スポンサード リンク
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