RNA

Genetics as it applies to evolution, molecular biology, and medical aspects.

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MIA6
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RNA

Post by MIA6 » Mon Apr 30, 2007 1:18 am

I was confused about the functions of mRNA and tRNA. On my book, it says "At the ribosomes, the genetic code carried by the mRNA will be translated into a sequence of amino acids.","Before amino acids can be joined to make a polypeptide chain, however, they must be transported to the ribosomes. This is the function of the third form of RNA, transfer RNA (tRNA)." So I am really confused now because these two sentences are contradicted in my opinion because if you see the first sentence, it says ribosomes, so if RNA is now in the ribosome, then it is not mRNA but tRNA according to the second sentence. My teacher told me that tRNA transports amino acids in the cytoplasm to the ribosomes, so mRNA is not supposed to be in the ribosomes? BTW, Is mRNA translated into amino acids or tRNA? Where does it happen? in the nucleus? Hope you can answer my questions, thank you.

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ping
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Post by ping » Mon Apr 30, 2007 7:33 am

"At the ribosomes the genetic code carried by the mRNA will be translated into a sequence of amino acids."This means that the mRNA determines the sequence ot the synthesied polypeptide.But the genetic code in mRNA only determines which is the next amino acids,mRNA cannot find it and bring it to the polypeptide chain.This is what does the tRNA.tRNA transports tha amino acids to the ribosome.The second structure of the tRna has four parts:one for the amino acid,one for the codon in mRNA(anticodon),(that's the way the correct amino acid,carried by the tRNA is added),one for the enzyme aminoacyl-tRNA-transferase (for the peptide bond), and the last one is for contact with the ribosome.

blcr11
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Post by blcr11 » Mon Apr 30, 2007 7:51 am

A tRNA molecule carries an anticodon loop that is complementary to the correct triplet for its particular amino acid. The tRNA is also chemically bound to its amino acid (the tRNA is said to be “charged” when it is linked with its amino acid). Both mRNA and tRNA are on the ribosome as the message is translated into protein. This is oversimplifying a bit, but as each triplet of the message is exposed, calling for the next amino acid, the appropriate charged tRNA-AA complex recognizes the triplet and the codon-anticodon hybridize. As a result, the amino acid carried by the tRNA is now in place for addition to the growing protein chain. The mRNA then “moves over” to expose the next triplet, and the process continues until it reaches the stop codon. All of this takes place on the ribosome, assisted by a host of translation, elongation, and termination factors--and the ribosome itself, of course.

I’d be surprised there wasn’t a diagram to go along with the text. Maybe the diagram would make more sense to you.

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