Ribosomal RNA
Phillips Huang
BMS 265
rRNA Nomenclature
• Named based on sedimentation rates,
measured in Svedberg units (S)
• Larger sedimentation coefficients indicate
faster sedimentation rates
• Larger rRNAs sediment faster
rRNA Discovery
• First discovered in the
1930s as part of the
microsome by Albert
Claude
• Characterized as a
ribosomal component
in the 1950s by
George Palade
Large Ribosomal Subunit
• rRNA largely
responsible for 3D
structure
• Peptidyl transferase
center (PTC) composed
of rRNA
• A, P and E sites made
up mainly of rRNA
Small Ribosomal Subunit
• Atomic structure
published in 2000
• Decoding center
composed entirely of
rRNA
rRNA Biogenesis in Eukaryotes
• In prokaryotes, rRNAs are also synthesized as
one primary transcript
Mechanism of action:
Translation initiation in Prokaryotes
• Translation initiation in eukaryotes involves
binding of ribosomal components first to the
mRNA 5’ cap
Mechanism of action:
Translation elongation
Residues of rRNA help to stabilize
the mRNA:tRNA complex
Peptide Bond Formation
• Involves nucleophilic attack of α-amino group of
aminoacyl-tRNA on carbonyl carbon of peptidyltRNA
Target carbonyl carbon is
protected from hydrolysis prior to
reaction
Hypothesized transition state
Mechanism of action:
Translation termination
rRNA as a Tool
• Phylogenetic studies
– rRNA sequences are
highly conserved across
species
• In vitro translation
systems
– Used when
overexpressed protein is
toxic, rapidly degraded
or insoluble in cells
lancelets
hagfish
lamprey
gnathostome
Role in Human Disease
• Mutations in mitochondrial
rRNA
– Susceptibility to
aminoglycoside-induced
hearing loss
• Changes to rRNA in
cytoplasmic ribosomes
– Defective pseudouridylation
and X-linked Dyskeratosis
Congenita (X-DC)