Thursday, March 31, 2011
hydroxyapatite and the rest
In chapter 4 Neil Shubin addresses the hydroxyapatite within teeth. The hydroxyapatite was initially suggested for internal use against deterioration due to chemical and mechanical digestion that occurs in the mouth. Furthemore, conodants are mentioned as the first organisms to have teeth. When was hydroxyapatite introduced and how does the time relate to the formation of chitin and calcium carbonate throughout evolutionary history? Discuss the chemical composition of hydroxyapatite.
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ReplyDeleteThe formula for hydroxyapatite is Ca5(PO4)3(OH), but is usually written Ca10(PO4)6(OH)2 to show that the crystal unit cell comprises two different components. Hydroxyapatite composes about 50% of humans’ bones and is essential for the integrity of the structure of the bones (Mineral Data Team 1).
ReplyDeleteHydroxyapatite first appeared in conodonts when conodonts first appeared around the late Cambrian period. The hydroxyapatite was found in their teeth and was used to make their teeth strong and durable. The hydroxyapatite found in the teeth of conodonts and other animals is a form called bone mineral. Conodonts used their teeth for scavenging or predation, which gave them a selective advantage over other organisms that did not have mineralized teeth. In some other species around the same period, the organisms had mineralized armor that helped protect them from predators. One possible hypothesis for the transition to mineralized bones and armor is that the eating habits of the early creatures changed. Early vertebrates were only bottom feeders, but as time went on, the animals became larger, and could eat other animals. Therefore, the minerals from these animals ended up providing the necessary supplies to initiate mineralization (Campbell 705). However, I think that there is another possibility. As the animals became larger, the need for a stronger support system grew, so they started to have mineralized bone structures to support the more complex and larger organisms. While this might not be true, there is no evidence against it.
As vertebrates evolved further, stronger substances had to replace the weak minerals that were used to support the organisms. Chitin was developed over evolutionary time as an alternative armor and support system. Its chemical formula is (C8H13NO5)n. It first appeared in the Cambrian arthropods called trilobites. Many later arthropods maintained chitin as their primary form of support and protection. Chitin is also found in fungus, which might have evolved to use chitin independently of arthropods, which is an example of convergent evolution (Heppe 2).
benitorosenberg12@comcast.net
http://www.handbookofmineralogy.org/pdfs/hydroxylapatite.pdf
http://www.gmp-chitosan.com/en/products-services/chitin.html
Hydroxyapatite is commonly used as a filler to replace amputated bone or as a coating to promote bone ingrowth into prosthetic implants. Although many other phases exist with similar or even identical chemical makeup, the body responds much differently to them.
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