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← Evolution

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

  1. So why do we care about a variation
  2. in a protein or enzyme called Tyrosinase? With Tyrosinase
  3. is the rate limiting step in the production
  4. of melanin. There are many steps to making the
  5. pigment in melanin. And some of the first
  6. are converting a molecule called Tyrosine. Actually Tyrosine, the
  7. very amino acid we've learned about and is
  8. in our amino acid alphabet, into another molecule called
  9. dopa, and from dopa into dopaquinone. Tyrosinase
  10. performs this function, but it's pretty slow,
  11. actually. Compared to all the other steps you need to get melanin. This is the
  12. part that takes the longest. So this
  13. single nucleotide variation up here. The cytosine to
  14. an adenine. The change in amino acid
  15. from serine to tyrosine, ironically enough, causes, right,
  16. that's a missense mutation now. Which causes Tyrosinase to work 40 to
  17. 50% slower than it normally does. So if this is true
  18. we would expect to see a decrease in overall melanin because we're going to make
  19. it a lot slower. If we have less melanin
  20. we're going to have lighter skin. If we have lighter skin,
  21. we're going to have UV rays that are able to
  22. get into the cells. So that they can simulate vitamin
  23. D production. So this particular mutation will give
  24. you lighter skin. Where as this sequence promotes darker
  25. skin. Now there are actually several other genes
  26. that affect skin pigmentation and they all have multiple
  27. alleles that explain all kinds of intermediate pigmentation
  28. as well as red haired individuals. But this is
  29. just one example of how a single nucleotide
  30. variation in the coding region, causing a missense mutation
  31. from a Serine to Tyrosine, slows the enzymes
  32. function by 40 or 50%, allowing for less
  33. pigment in the skin, thus letting more sunlight
  34. in. To produce vitamin D. Of course the
  35. flip side of this is the more sunlight you let in the more risk you are
  36. for DNA damage. And that's why light-skinned people
  37. when they're in really UV intense regions are much
  38. higher risk for skin cancer than dark pigmented people. Let's go talk to
  39. somebody who knows quite a bit about living in hot, UV rich equatorial regions.