Download Amino acid and Protein

Genetic Codes
and
Translation
J a v a d
F a s a
J a m s h i d i
U n i v e r s i t y
o f
M e d i c a l
S c i e n c e s ,
D e c e m b e r
2 0 1 6
How is the information in a linear sequence of
nucleotides in RNA translated into the linear
sequence of a chemically quite different set of unitsthe amino acids in proteins?
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From RNA to Protein
The language is not the same
Nucleotides vs. Amino acids
An intermediate (tRNA)
The number of letters are not the same
4 Nucleotides vs. 20 Amino acids
Combinations of three nucleotides
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The Genetic Code
There are 20 amino acids
1 nucleotide for 1 AA = 4
2 nucleotide for 1 AA = 42 = 16
3 nucleotide for 1 AA = 43 = 64
Each genetic code is a consecutive groups of three nucleotides
Some amino acids are specified by more than one triplet
The genetic code is used universally in all present-day organisms, with some
exceptions
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The Genetic Code
This code was deciphered
by Marshall Nirenberg and
his colleges in 1961
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Reading Frame
Amino acid and Protein
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tRNA Structure
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tRNAs
Some 30-40 different tRNAs have been identified in bacterial cells and as
many as 50-100 in animal and plant cells.
The number of tRNAs in most cells is more than the number of amino acids
Also differs from the number of amino acid codons in the generic code (64) .
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Linking Amino Acids to tRNAs
Each tRNA molecule becomes linked to the one amino acid in 20 that is its
appropriate partner
Recognition and attachment of the correct amino acid depends on enzymes called
aminoacyl-tRNA synthetases
Most cells have a different synthetase enzyme for each amino acid (that is, 20
synthetases in all)
The aminoacyl-tRNA synthetase enzymes and the tRNAs are equally important in
the decoding process
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Amino acid activation
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The structure of the aminoacyl-tRNA linkage
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Two Adaptors for Translating the Genetic Code
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Amino Acids Are Added to the C-terminal End of a Growing Polypeptide Chain
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Ribosome Subunits
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A Polyribosome
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