Why don't tRNA and rRNA get translated?

[NPK]

This may sound like a stupid question, but why don't tRNA and rRNA get translated into protein? (I know what role tRNA and rRNA play in cells but what's stopping a ribosome attaching to them etc?)

 

Do the Bacterial ones not have Shine-Dalgarno sequences?

 

Do the Eukaryotic ones not have a 5' cap?

 

Do they quickly fold into their tertiary structure and not expose any binding sites for translation to begin?

[donkey]

interesting point, my totally ill-informed guess would be that they spontaneously fold into their tertiary structure.

 

It may also be worthwhile pointing out that tRNA has a lot of special, modified, bases (not A,C, U or G) which probably couldn't be "read" by the ribosome. I'm not sure how or when these bases are modified though so that might not be an important point...

[Dak]

I think (but am by no means sure) that the odd bases wouldnt be a problem, if it came to translation: pseudouracil would probably be mistaken for uracil, etc.

 

The reason is probably that the tRNA dont have any loose ends with start codons (?) to start transcription, and also that their tertary shape prevents them running through the ribosomal grove-thing (as donkey said).

 

hmm... interesting.

 

(hah -- and i call myself a molecular geneticist: that has got to be the pantsest answre to a genetics question ever given ).

[LucidDreamer]

I think the answers have already been given. tRNA, mRNA, and rRNA all undergo different post-transcriptional modifications. The mRNAs will fold in a way where the start codon and shine degarno sequence or 5' end cap stay accessible to the ribosomes. These components are essential to initiation of translation. The tRNAs will also undergo extensive post-transcriptional modifications and will fold into a clover like shape that does not have or present a translational initiation sequences. The individual components of rRNA will fold and form a complex much like a polypeptide enzyme, which makes them inaccessible to be translated and they lack translational initiation sequences as well.

[Dak]

Do you know wether tRNA and rRNA would get translated if for some reason they didnt get folded?

[LucidDreamer]

I don't think they would because they would still lack the accessible start codon and translation initiators (shine-degarno/5' cap) and as you mentioned they might get hung up on the modified bases. I don't know for sure though.

[Helix]

tRNA and mRNA do get transcripted. They are step 2 in transcription.

 

1--DNA is copied and converted to mRNA

2--mRNA (messengerRNA) goes to ribosomes

3--protein created based on mRNA message.

 

mRNA does get transcriped. It is the courrier that takes the DNA to get copied.

[donkey]

dude, transcription is the formation of an RNA representation of the DNA code (i.e. step 1 you mentioned above). Step 2, where mRNA is used as a blueprint for a protein is not transcription - that is translation!

[NPK]

tRNA and mRNA do get transcripted. They are step 2 in transcription.

 

1--DNA is copied and converted to mRNA

2--mRNA (messengerRNA) goes to ribosomes

3--protein created based on mRNA message.

 

mRNA does get transcriped. It is the courrier that takes the DNA to get copied.

That's not the point of the thread..it's about translation, not transcription. And mRNA does not get transcribed anyway.

[Helix]

responding to the two previous posts:

 

dammit you're right donkey, how could that evade me? in any case i think it's granted what I meant.

 

NPK--What i ment was that mRNA gets translated to the effect that the DNA sequence is contains is created into a protein. mRNA is the vehicle for translation, so by that process it does indeed get translated. I think you're missing the point that I am now speaking generally but specifically to what happens--mRNA gets translated.

[NPK]

responding to the two previous posts:

 

dammit you're right donkey' date=' how could that evade me? in any case i think it's granted what I meant.

 

NPK--What i ment was that mRNA gets translated to the effect that the DNA sequence is contains is created into a protein. mRNA is the vehicle for translation, so by that process it does indeed get translated. I think you're missing the point that I am now speaking generally but specifically to what happens--mRNA gets translated.[/quote']

 

You might want to read the original post again. I wasn't asking if mRNA gets translated. I know about that. I was asking about tRNA and rRNA.

[Helix]

Right, I saw that. But tRNA and rRNA play similar roles as far as having DNA sequences that eventually get sequenced.

 

Quote from a biochemistry website:

 

"tRNA is the information adapter molecule. It is the direct interface between amino-acid sequence of a protein and the information in DNA. Therefore it decodes the information in DNA."

 

And rRNA is the "machinery" so it has to, by nature of its role, be translated (translated meaning its DNA or RNA sequence being made into amino acids).

Another quote:

"Ribosomal RNA (rRNA) is a component of the ribosomes, the protein synthetic factories in the cell."

[LucidDreamer]

And rRNA is the "machinery" so it has to' date=' by nature of its role, be translated (translated meaning its DNA or RNA sequence being made into amino acids).

Another quote:

[i']"Ribosomal RNA (rRNA) is a component of the ribosomes, the protein synthetic factories in the cell."[/i]

rRNA is not translated. rRNA is transcribed from several different component pieces of RNA that come together to form a RNA complex. That complex performs an enzymatic role in the ribosomes. The rRNA complex, together with several proteins forms a ribosome, which translates mRNA into proteins.

[Helix]

Okay, I mis-remembered that. But tRNA does get translated, it is the intermediate.

[LucidDreamer]

Both rRNA and tRNA are important to the process of translation, but they are not translated themselves. There are approximately 20 different kinds of tRNA molecules that all attach to a different amino acid. These 20 tRNAs also have a unique three base code, called an anticodon, that is complementary to the three base code on the mRNA, called the codon. Their role as an intermediary is in their function of bringing amino acids together with nucleic acids so that the ribosomes can interpret the mRNA code to produce the correct peptide (small protein).

[Helix]

Right, I know all of that. But what I am saying is that their DNA (RNA) sequence gets turned into amino acids one way or another.

[LucidDreamer]

Accidentally reposted. Where is the delete post button anyway.

[donkey]

Right, I know all of that. But what I am saying is that their DNA (RNA) sequence gets turned into amino acids one way or another.

tRNA isn't and is never turned into a protein / amino acids. tRNA is a functional RNA molecule.

[Helix]

No I didn't say it was, I am making an arcane point. I am saying that the DNA sequence that tRNA has gets turned into an amino acid because it is one. tRNA's attach their anticodon's to the codon and bring the amino acid with them. Therefore, the sequence tRNA's contain make it to the protein because they are the instructions for the amino acids.

[donkey]

ok but you can't say "tRNA does get translated" - that's not correct. That's like saying "google language tools gets translated" (which makes no sense) instead of saying "google language tools helps translate english to german".

 

I think that's where the confusion arose anyway

[Helix]

Right, at the offset I should have said I am nit-picking.

[MaximusPrime]

Hello, just a clarification:

 

tRNA does not get translated. It is transcribed in the nucleus and then undergoes post transcriptional modification. Next it is exported to the cytoplasm where it finds its corresponding aminoacyl tRNA synthetase. This is a special enzyme that "charges" the tRNA by adding an amino acid to it. The charged tRNA then floats in the cytoplasm until it is needed.

 

The tRNA is called upon when a nearby translating ribosome gets to a codon that matches the chargered tRNA's anticodon. Our adventurous tRNA is then sucked into the ribosome and positioned in just the right way so that the rRNA within the ribosome can transfer the tRNA's amino acid onto the end of whatever protein the ribosome is in the process of making. Once this peptidyl transfer reaction occurs, the tRNA is unceremoniously spat out the other end of the ribosome where it is once again wrapped in the embrace of a tRNA synthetase, recharged, and sent back to continue it's tireless work.

 

 

As to the original question, I'm actually curious about how tRNA and rRNA avoid being mistaken for viral RNA. Since they are generally uncapped, how would a cell know not to destroy them? My best guess is that the free 5' ends of these molecules are hidden inside secondary structure, but I'd love to know if there's more information out there.