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Biology Translation

Teacher/Instructor Patrick Roisen
Patrick Roisen

M.Ed., Stanford University
Winner of multiple teaching awards

Patrick has been teaching AP Biology for 14 years and is the winner of multiple teaching awards.

Translation is the process in biology in which a ribosome uses the information stored in messenger RNA (mRNA) link together the sequence of amino acids which form proteins. Translation is preceded by transcription in which the mRNA is formed. tRNA then brings amino acids to the ribosome which latches to the mRNA, matching the codons in the mRNA to the tRNA. The three steps to translation are initiation, elongation and termination.

Translation is the second half of protein synthesis now it's called translation because you're taking a sequence of a's, u's, g's and c's from RNA and you're turning them into a sequence of amino acids which is the language of proteins so you're having this go from the nucleic acid language to the protein language and that's why they're called translation.

Now it's done primarily by the ribosomes, the small little bundles of RNA and enzymes that are floating around side of the cytoplasm but it also requires of course that messenger RNA that's the guide for the ribosomes as well as other helping molecules called t-RNa for transfer RNA and other factors sometimes they're called initiation factors or elongation factors or termination factors. Now that brings up, what are steps of translation?

And in general they're called initiation and that's where you bring together that two halves of the ribosome the small and the large subunit, you bring together the messenger RNA with that small subunit, you bring together the t-RNA that begins it as well as any other required factors.

Then elongation is where you start adding more amino acids to the growing chain or protein.

And finally termination is when you end this process. Now you can see here I wrote aug equals the start codon that's the clue to the ribosomes where in this messenger RNA strand should you begin your translation process now how does it know how to end? Well it ends where it encounters the codons uaa or uag or uga those are otherwise known as the stop codons.

Now let's go ahead and take a look at this video from youtube we'll go ahead and make it large and here we can see the messenger RNA is leaving the cytoplasm leaving the nucleus and headed towards a small subunit we'll go ahead and pause it here real quick so that's the small subunit of the ribosome the big flat pancake that has a groove in it. You can see the messenger RNA is being aligned in that groove. Now the weird little curly cue things that you can see floating around and approaching, those are t-RNA's there are strands of RNA that have a special folding and on one end of them they have an amino acid added to them by a particular enzyme and it's called a charged amino aci- charged t-RNA now because of that amino acid. And on the other portion of t-RNA you have something called the anticodon which will match up following the standard base pairing rules for RNA to the codon of messenger RNA we'll go ahead and get started again and we'll see the t-RNA for the start codon brings on with it it's amino acid and here we see it approaching from the left hand side of the screen and you'll see this weird little green-black that's the symbol for the methionine amino acid. We see the t-RNA is anti to the codon now the large subunit obviously is a large thing comes in slides in and we're now finishing the process known as initiation and we're ready to begin elongation.

And if we se- see through oh that weird little thing that juast approached and it's entering in on what's called the a site that the next t-RNA it too has an anticodon that matches up and it brings with it its weird little green case or whatever and that alien thin that wasn't what you thought that's an enzyme that joins together the amino acids and now the first t-RNA can leave because it's lost amino acids it's left it behind in the rimbosome and so the ribosome now shifts down one more codon that movement sometimes called translocation opening up the a site now for the next t-RNA to come in it matches up its anticodon to the codon again our enzyme joins the next amino acid to the growing chain and that's what's happening we're just going on choom choom choom choom choom adding in amino acids till finally we're going to hit the start codon and the protein will be broken off from the last t-RNA and everything will just fall apart hope by termination factors and that's translation.