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← Ribosomes

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Showing Revision 1 created 09/29/2013 by Cogi-Admin.

  1. Okay, this is a really tricky problem. But the answer is the last one right
  2. here. Methianine or M, P or Proline, D or Aspartate, or S or Syrine. Now if
  3. you had trouple getting this, let's walk through
  4. it really quick. I can immediately get rid
  5. of these first three answers over here for
  6. one very important reason. We have one start
  7. codon and it's Methanine. A ribosome is looking for that start codon
  8. and if I read my mRNA ACA, no that's not it, CAG, no that's not it, AGA, no
  9. that's not it, GAU, no that's not it, AUG, there it is, AUG. AUG's my
  10. star codon. Right? That means I get a
  11. Methionine. None of these start with Methionine. All
  12. of these start with Threonine which is an
  13. ACA. So, if you just start at the beginning,
  14. you would have started with the Threonine and probably
  15. gotten one of these three answers. This is the
  16. one, I think if you end up going all the way to the very end, and the second
  17. one, is if you might have noticed a stop
  18. codon. ACAGAUGCCUGA stop, right? And some of you might
  19. have stopped completely and just put TDA, or if you
  20. stopped and then kept going, right, that would not have
  21. been accurate, as we see over here. Is a better
  22. example of why you wouldn't want to do that. We know
  23. now that we want to start at AUG, okay, so now
  24. we know the first one is Methionine, and because we
  25. have a non-overlapping code, our next one is CCU. We
  26. don't do UGC or GCC, the next codon is CCU.
  27. Go over here. CCU is Proline, so we have a P. They all have a P. The next
  28. one is GAU. GAU. Aspartate D, they all have
  29. that. The next one would be UCA, UCA Syrine right here.
  30. So the next one should be Syrine. They all have that. And then we get to UGA.
  31. And you'll notice that UGA is one of
  32. our special stop codons. This would tell the ribosome
  33. to stop translating right here. And actually the
  34. only one that stops is MPDS, this last one
  35. right here. The other ones actually keep going.
  36. ACC, ACC. Is Threanine, right? They actually thought that
  37. they should drop in another amino acid and keep
  38. on going. When you get to a stop codon,
  39. you stop translating. From AUG to UGA, this would
  40. be our actual code that gets turned into protein.