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Old 05-12-2012
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Molecular Transfer RNA Two Arms Sequences!

I need someone to clarify this for me please!

Regarding the t-RNA, it has two arms.
1) Amino-acyl arm: for binding of amino acid
2) anti-codon arm: for binding of mRNA

-The amino-acyl arm has a specific sequence that is always CCA, a sequence that is always the same and doesnt change, right?
-Does the anti-codon arm have a specific sequence? One that is also constant and always the same?
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Old 05-12-2012
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Thumbs Up Its important..

yes,
you are right,
aminoacyl arm sequence never changes its CCA...
but anticodon arm can be whatever codon.
In all the books example its methionine, AUG,
but, understand, that transfer RNA does all its work by this anti codon arm by attaching different anticodon sequences whichever it has to transfer.
So it can be any codon,..

I hope i sound clear..:-)
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Just like one_destiny told you.

The genetic code is composed of 64 codons (3 are stop codons) so 61 codons.

For each of these mRNA codon, you need a corresponding anti-codon tRNA sequence, therefore you need 61 different types of t-RNAs in each cytoplasm.

However, remember that the genetic code is 'degenerate', several condons can code for the same amino acid (except Methionine and Tryptophan, see this beautiful question here tRNA Anti-codon Wobble)

Therefore, you don't need actually 61 tRNAs in each cell,. A smaller number is actually required to satisfy the translation needs of all human amino acids, I think 30 tRNAs in each cell is enough (am not sure about the number) but you got the concept.

-
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Old 05-12-2012
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Yes i see, so:

-amino-acyl arm: binds to the amino acid, and always has a sequence of CCA

-anti-codon arm: binds to mRNA, and has a changing sequence unique to the corresponding codon it wants to bind to.

Thnx guys! I can now go to sleep with a new concept in my head
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Old 05-12-2012
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One last question guys. I want to get this down once and for all!

If the anti-codon arm's specificity to a codon on the mRNA is done through a unique sequence.

Then how are specific amino acids chosen and picked up by tRNA's? Knowing that the sequence never changes. (Is it done by a specific aminoacyl-tRNA transferase?)

What i mean by the question is,
-anti-codon arm specificity: done through the specific sequence to a corresponding codon
-amino-acyl arm specificity: done through aminoacyl-tRNA synthetase?

Last edited by Renaissance; 05-12-2012 at 10:19 AM.
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That's why you need different t-RNA for different amino acids attached in the translation process.

Each t-RNA specifies it's own amino acid according to what anti-codon it harbors.

-
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Quote:
Originally Posted by Renaissance View Post
-anti-codon arm: binds to mRNA, and has a changing sequence unique to the corresponding codon it wants to bind to.
The sequence does not change, you change the whole t-RNA molecule to get a new anti-codon.

-
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Old 05-12-2012
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Awesome!
Thnx, i really appreciate it

For anyone who's reading the thread, here's the big picture:

tRNA, what does it do?

Picks up amino acids (by binding them to the amino-acyl arm of the tRNA), and takes them to mRNA (by binding the anti-codon arm of the tRNA to the codon of the mRNA), so that they can be used in protein synthesis.

Good night!
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