How is rRNA synthesized

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Area of ‚Äč‚ÄčExpertise - Biochemistry, genetics

The ribosomal RNAs (rRNAs) form the main component of the ribosome, the site of protein biosynthesis. Ribonucleic acids and ribosomal proteins are organized into two subunits, the small and the large subunit of the ribosome. For historical reasons, these subunits are called 30S and 50S subunits in prokaryotes in Svedberg units; both together form the 70S ribosome. The slightly larger 80S ribosomes of the eukaryotes are made up of a 40S and a 60S subunit.

The 70S prokaryotic ribosome contains the 23S, 16S and 5S rRNA. The 80S mammalian cell ribosomes are composed of four rRNAs of 28S, 18S, 5S, and 5.8S. While the rather flexible small subunit of the ribosome is primarily responsible for the contact between mRNA and tRNA, the rather rigid large subunit catalyzes the peptide bond between the amino acids.

Tab. 1
An overview of the rRNAs of prokaryotes and eukaryotes
OccurrenceRibosome subunitrRNAsribosomal proteins
Prokaryotes30S subunit16S rRNA approx. 20 proteins
 50S subunit23 S rRNA, 5S rRNAapprox. 30 proteins
Eukaryotes40S subunit18S rRNA33 proteins
 60S subunit28S rRNA, 5S rRNA, 5.8S rRNA49 proteins

The genes for rRNAs occur in several copies in the genome of eu and prokaryotes and are synthesized as a larger precursor molecule from which the individual rRNAs are then cut out by RNases.

See also: ribosome, translation

Learning units in which the term is dealt with

Introduction to Gene Expression60 min.

biochemistryProtein synthesisTranscription and gene regulation

This learning unit is an introduction to the basics of gene expression in prokaryotes and eukaryotes.