Sunday, March 10, 2013
Prompt 1: ApoE4 and Big Idea 4
On pages 54-56, Moalem relates the loss of folic acid and the creation of vitamin D. Folate or folic acid is fundamental to DNA replication as well as helping produce red blood cells, while vitamin D is important to multiple processes in the body. The skin protects the body's stores of folate but is also the site of vitamin D manufacturing. Differences in skin color relates to the amount of ultraviolet light absorbed. Darker skin protects against the loss of folic acid but also hinders the creation of vitamin D. This contradiction relates to Big Idea 4: Biological systems interact, and these systems and their interactions possess complex properties.
Cholesterol is vital to the synthesis of vitamin D. A protein called apolipoprotein E (ApoE4) keeps cholesterol levels high to maximize conversion to vitamin D with limited UV exposure. ApoE4 is common in dark-skinned people as well as light-skinned people. Why would both Europeans and Africans have the ApoE4 gene if Africans have too much sun and Europeans have too little? Research ApoE4 and its relation to increased risk to a disease such as Alzheimer's, atherosclerosis, and type III hyperlipoproteinemia.
(Posted by Tina Tian, ttian4@students.d125.org)
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Response #3 4/9/13
ReplyDeletehttp://survivalofsickestinselberger.blogspot.com/2013/03/prompt-1-on-folic-acidvitamin-d-and-big.html
ApoE4 and Big Idea 4
Vitamin D plays a factor in many parts of the human body. It has been said to improve mood, cancer resistance, autoimmune diseases, bone density, and more. You produce Vitamin D naturally through a chemical reaction from sunlight on your skin. As Dr. Moalem explains on pages 55-57, populations of people have gained adaptations to protect themselves from harmful UV rays from sunlight, and also to maximize Vitamin D production. In Africans, we see the dark skin color. The dark skin acts to protect them from harmful UV rays and protect folate. However, sometimes the dark skin worked too well and, would prevent efficient Vitamin D production. This relates to Big Idea 4 in that two systems interact with each other and also the environment. Also, as populations moved north were they were less exposed to sunlight, the dark skin did not benefit them as it prevented them from properly producing Vitamin D, thus they evolved towards a paler complexion that allowed for the absorption of sunlight needed to make Vitamin D.
However, both populations (those with dark skin, over exposed to sunlight, and those with pale skin receiving little sunlight) have the gene ApoE4. The ApoE4 is a selective advantage because it keeps cholesterol levels high to maximize Vitamin D conversion. The two seemingly different populations have both acquired this gene over time. The dark-skinned people exposed to a great amount of sunlight would want the ApoE4 gene to aid in maximizing Vitamin D conversion because their dark skin and the protecting of folate prevents them from keeping Vitamin D. Thus, with the ApoE4 gene, the dark-skinned people would be able to better utilize the sunlight they are exposed to. On the other hand, for populations of people with lighter skin, having the ApoE4 gene is a selective advantage so that they can take advantage of what little sunlight they are exposed to and produce as much Vitamin D as possible. As we have previously studied in the Evolution unit, these adaptations make the organism best suited for its environment and help the organism reach its ultimate evolutionary goal: to survive and reproduce.
ApoE4 can also harm the body. It has been linked to increase risk of Alzheimer’s disease. People who inherit one copy of the gene are three times as likely to develop Alzheimer’s and people who receive a copy of the ApoE4 gene from both parents are twelve times as likely to develop Alzheimer’s disease. A study led by Dr. Berislav Zlokovic showed that the ApoE4 gene “triggers a cascade of events that damages the brain's vascular system." It also shows that damage to the brain’s vascular system may play a key role in Alzheimer’s disease. Thus, the ApoE4 gene triggers damaging of a system that coincides with the onset of Alzheimer’s making those with the ApoE4 gene more likely to develop the disease.
Sources:
San Francisco Chronicle- Vitamin D: What’s behind the interest
http://www.sfgate.com/health/article/Vitamin-D-What-s-behind-the-interest-4386352.php
Apolipoprotein E controls cerebrovavascular integrity via cyclophilin A, Nature 5/24/12
Rachel Chang (rchang4@students.d125.org)