23S ribosomal RNA
= 23S ribosomal RNA
{c}
<23S ribosomal RNA> is the large <ribosomal RNA> component of the 50S <large ribosomal subunit> in <bacteria> and <archaea>. It forms much of the subunit's structural framework and the RNA-based environment of the <peptidyl transferase center>. The functional <RNA> is distinct from the <DNA> sequence from which it is transcribed: a genomic sequence record and a mature ribosomal component describe different physical molecules.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others>[From RNA to Protein, composition and functions of ribosomal subunits]{ref}
Structural experiments with an archaeal <large ribosomal subunit> placed two <substrate analogues> against conserved regions of <23S ribosomal RNA>. The absence of nearby <protein> side chains at the bond-forming position supported the conclusion that the <ribosome> is a <ribozyme>.<The structural basis of ribosome activity in peptide bond synthesis by Poul Nissen and others>[Abstract, domainV contacts and RNA-based active site]{ref}
The 23S label refers to a <sedimentation coefficient>, not 23 <nucleotides>. It must not be added as though it were a molecular mass: the 50S <large ribosomal subunit> contains <23S ribosomal RNA>, <5S ribosomal RNA> and <ribosomal proteins>, and its sedimentation depends on the assembled object's shape and resistance to motion.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others>[Ribosome sizes and sedimentation labels]{ref} Thus a measurement of an isolated RNA component and a measurement of the complete subunit need not carry the same S value.