Download tRNA, rRNA, and RNAi Transfer RNA (tRNA) Characteristics of tRNA

Transfer RNA (tRNA)
tRNA,
tRNA, rRNA,
rRNA, and RNAi
Chapter 14 continued
Characteristics of tRNA
tRNA:
tRNA: Linking the genetic code to
proteins.
Figure 14.22
• Each tRNA attaches to a particular amino
acid
– Carries it to Ribosome
• tRNA has rare Modified Bases
– Made by tRNA-modifying enzymes
• Secondary structure called a cloverleaf
3-D Structure
Ribbon Model
Flattened
Cloverleaf Model
Figure 14.21
The names of the arms come from
the presence of modified bases.
DHU: dihydrouridine
TΨC: Thymine, pseudouracil,
cytosine
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Transfer RNA Gene Structure
tRNA Introns
• E. coli: single copies of some tRNA
genes, multiples of others.
• Splicing of tRNA introns different from
spliceosomal introns.
• Eukaryotes: Many copies of each tRNA
gene
• Intron cut at both ends with an
endonuclease.
Ribosomal RNA (rRNA)
rRNA)
rRNA:
rRNA Building block of the
ribosome
Characteristics of rRNA
• rRNA genes present in multiple copies
• Extensive post transcriptional modification
• The ribosome:
– Several rRNA molecules and many proteins
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In both Bacteria and
Eukaryotes, tRNA and rRNA
are modified after
transcription.
snoRNAs (small nucleolar
RNAs) help to cleave and
modify eukaryotic rRNAs
into mature ribosomes.
Small Interfering RNAs and
MicroRNAs
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RNAi
RNAi and Fluffy
• Abundant in eukaryotes
• Humans have 200+ miRNA genes
• May have evolved as “an immune system” for
the genome
• Can use RNAi to “knock down” expression of
specific genes
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