Primary & secondary structure
tRNAs have similar sequences of 73 to 93 nucleotides
3' end always terminates with the sequence CCA,
with the 3' hydroxyl of the ribose of the terminal A
being the point of covalent attachment of the amino acid
Contain a number (7-15%) of unique/modified bases.
These are post-transcriptionally modified after synthesis by RNA polymerase.
In particular, adenosine (A)
in first or 5' position of the anticodon (corresponding to the third or
3' position of the codon) is always modified to inosine (I)
which lacks the amino group on the purine ring. Inosine can base-pair
with A, U
or C and thus
accounts for much of the degeneracy of the Genetic Code ("Wobble
tRNAs have cloverleaf secondary structure due
to four base-paired stems
The cloverleaf contains three non-base-paired loops:
D, anticodon, and TpsiC loop
The tertiary structure of tRNA is best described as a compact
The anticodon is a single-stranded loop at
the bottom of the Figure which later base-pairs with the triplet codon
The amino acid is attached to the terminal A
on the upper right.
The active sites (anticodon and amino acid)
are maximally separated.
As in proteins, the tertiary structure is dictated by the
The tertiary structure is stabilized by base pairing and
Two areas (anticodon stem and acceptor stem) form double
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