Each different tRNA binds to a specific amino acid and transfers it to the ribosome. Mature tRNAs take on a three-dimensional structure through intramolecular basepairing to position the amino acid binding site at one end and the anticodon in an unbasepaired loop of nucleotides at the other end.
There are different tRNAs for the 21 different amino acids. Most amino acids can be carried by more than one tRNA. In archaea and eukaryotes, each pre-tRNA is transcribed as a separate transcript. Multiple nucleotides in the pre-tRNA are chemically modified, altering their nitorgen bases. On average about 12 nucleotides are modified per tRNA. But over other modifications can occur. A significant number of eukaryotic and archaeal pre-tRNAs have introns that have to be spliced out. N - val - ile - leu - C protein.
This is a logical , not a biochemical , relationship: Because mRNA is transcribed from the template strand, it " looks like " the sense strand except for ' U '. Protein sequences can be read directly from DNA : Read the sense strand in the 5' 3' direction, Substitute ' T ' for ' U ' in the code table [or in your head] Computer programs Chromas , Sequencher, etc.
There are three reading frames on either strand X two 5' 3' strands six possible ways to read dsDNA Open Reading Frames suggest protein sequences.
Right, I know all of that. No I didn't say it was, I am making an arcane point. Therefore, the sequence tRNA's contain make it to the protein because they are the instructions for the amino acids. That's like saying "google language tools gets translated" which makes no sense instead of saying "google language tools helps translate english to german". 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. 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.
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Sign in here. We have placed cookies on your device to help make this website better. You can adjust your cookie settings , otherwise we'll assume you're okay to continue. Share More sharing options Followers 0. Recommended Posts. NPK Posted August 31, Posted August 31, Do the Bacterial ones not have Shine-Dalgarno sequences? Do the Eukaryotic ones not have a 5' cap?
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