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In molecular biology, ribosomal ribonucleic acid (rRNA) is the RNA component of the ribosome, and is essential for protein synthesis in all living organisms. It constitutes the predominant material within the ribosome, which is approximately 60% rRNA and 40% protein by weight. Ribosomes contain two major rRNAs and 50 or more proteins. The ribosomal RNAs form two subunits, the large subunit (LSU) and small subunit (SSU). The LSU rRNA acts as a ribozyme, catalyzing peptide bond formation. rRNA sequences are widely used for working out evolutionary relationships among organisms, since they are of ancient origin and are found in all known forms of life. ==Structure== The ribosomal RNAs complex with proteins to form two subunits, the large subunit (LSU) and small subunit (SSU). mRNA is sandwiched between the small and large subunits, and the ribosome catalyzes the formation of a peptide bond between the two amino acids that are contained in the rRNA. A ribosome also has three binding sites called A, P, and E. * The A site in the ribosome binds to an aminoacyl-tRNA (a tRNA bound to an amino acid). * The amino (NH2) group of the aminoacyl-tRNA, which contains the new amino acid, attacks the ester linkage of peptidyl-tRNA (contained within the P site), which contains the last amino acid of the growing chain, forming a new peptide bond. This reaction is catalyzed by peptidyl transferase. * The tRNA that was holding on the last amino acid is moved to the E site, and what used to be the aminoacyl-tRNA is the peptidyl-tRNA. A single mRNA can be translated simultaneously by multiple ribosomes.. 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「Ribosomal RNA」の詳細全文を読む スポンサード リンク
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