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RNA
3 major classes:
mRNA
tRNA
rRNA
2-5%
10-15%
80-85%
mRNA - number of different mRNAs in a cell can range from 100s to 1000s &
sizes can differ from 100s to 1000s nucleotides
In bacteria, mRNA synthesized, utilized and degraded continually so constant
turnover, t1/2 of mRNA ~2 min
tRNA - most cells have 60-70 different tRNAs (74-95 nts)
rRNA - E.Coli ribosomes have: 5S (120 nt), 16S (1542 nt), 23S (2904 nt)
Eukaryotic ribosomes have: 5S (145 nt), 18S (1869 nt), 28S (5025 nt),
5.8S (157 nt)
In eukaryotes, mitochondria & chloroplasts contain DNA and ribosomes, so
euks can have > 1 different sets of mRNAs, tRNAs and rRNAs
Other (non-coding) ncRNAs:
snRNA (small nuclear) - involved in mRNA synthesis, removal of intervening seq and polyadenylation
snoRNA (small nucleolar) - process rRNA precursors in euk nuclei
7S RNA - in cytoplasmic RNP, involved in transport of proteins through membrane
siRNA (small interfering) - 20-25 nt double-stranded RNA molecules that play a variety of roles in biology,
most notably in RNA interference (RNAi)
piRNA (piwi interacting) - 29-30 nt RNA molecules expressed in mammalian testes; forms RNA-protein
complexes with Piwi proteins; complex linked to transcriptional gene silencing of retrotransposons and
other genetic elements in germ line cells
gRNA (guide) - RNA that guides the insertion of uridines into mRNAs in trypanosomes in a process known
as RNA editing
Riboswitches - RNA elements found in non-coding regions of mRNA molecules, gene expression is
modulated when metabolite binds directly to the RNA. Many riboswitches, once liganded, repress
expression of nearby genes involved in the synthesis of the metabolite, providing an efficient feedback
mechanism of genetic control
Also other catalytic RNA molecules - RNA molecules capable of self-splicing and self-cleavage
Nucleotides & Nucleic Acids
Hydrolysis of RNA
Nucleotides & Nucleic Acids
RNA structure
Single-stranded (ss) RNAs
Nucleotides & Nucleic Acids
RNA structure - M1 RNA from RNase P
Nucleotides & Nucleic Acids
RNA structure - rRNA
Nucleotides & Nucleic Acids
RNA structure - tRNA
Nucleotides & Nucleic Acids
RNA structure - tRNA
 = pseudouridine
I = inosine
T = ribothymine
D = 5,6-dihydrouridine
m1I = 1-methylinosine
m1G = 1-methylguanosine
m2G = 2-methylguanosine
Pu = purine
Py = pyrimidine
G* = 2’-O-methylguanylate
+7
Bulge loop
Interior loop
Bulge loop
Interior loop