Ribosomal RNA (rRNA) is transcribed as precursor molecules that are processed into the mature rRNAs that make up parts of ribosomal subunits. In eukaryotes, two long precursor rRNA molecules are transcribed, one producing 5S rRNA and the other producing 28S, 5.8S and 18S rRNAs. rRNA processing involves cleavage of the precursor molecules by ribonucleases to remove spacer sequences and produce the functional rRNAs, which occurs through a series of cleavage steps in the nucleolus that generate intermediates before the final mature rRNAs are released.
2. Introduction
Ribosome consist of r RNA (65%) and protein(35%)
Ribosomal RNA (rRNA) :Along with numerous proteins,
helps form the large and small ribosomal subunits that
unite for translation of mRNA
rRNAs are transcribed as large precursor molecules that
are cleaved into smaller RNA molecules by removal and
discarding of spacer sequences intervening between the
sequences of the different RNAs.
The four rRNAs in eukaryotes are first transcribed as two
long precursor molecules. One contains just the pre-
rRNA that will be processed into the 5S rRNA; the other
spans the 28S, 5.8S, and 18 S rRNAs.
5. What is r RNA processing ?
It is the process of modification, mainly through
cleavage & or splicing, of primary RNA transcripts so as
to release functional RNA molecules from them.It is
carried out by ribonucleases (RNases) that cleave RNA.
6. How actual r RNA processing
takes place ?
Processing of 45s molecules occurs
inside nucleolus.
45s molecules tightly associated
protein forming ribosome (RNPS)
First cleavage: occurs at site I &
remove 5' terminal leader sequence, produces 41s
intermediate & 18s.
Second cleavage: occurs 41s intermediate at site
3'generates 32s intermediate.
Final cleavage: separation of 32s intermediate into 28. 5.8s
Processed rRNA 28s. 5.8s & 18s
