On page 45, Shubin writes, “there is a deep similarity among every cell inside our bodies: all of them contain EXACTLY the same DNA”. There are new studies out that are now contradicting this most basic assumption that almost all people make. Explain why this assumption is wrong and what differences are being brought to light in these new studies.
Matt Micucci (coochqbk@sbcglobal.net)
A study performed in 2009 gave light to a very big flaw in a seemingly universal rule about human DNA: Every cell in the human body has the same exact DNA. However, a group of scientists in Montreal proved this assumption was wrong in the journal Human Mutation. The group wanted to prove the validity of the blood-testing process that is used to analyze what is going on with genetically diseased human tissue. This process used to seem full proof because blood cells and tissue cells were thought to have the same exact DNA, so the blood cells’ DNA would reflect the flaw in the tissue cells’ DNA, thus causing disease. Surprisingly enough, the scientists discovered that the BAK gene, “a gene that controls cell death”, was amazingly different in blood cells compared to tissue cells (Sciencedaily.com “DNA Not The Same In Every Cell Of Body: Major Genetic Differences Between Blood And Tissue Cells Revealed”). This discovery created a decrease in the accuracy of blood tests: "In multi-factorial diseases other than cancer, usually we can only look at the blood," explained Gottlieb, a geneticist with McGill's Centre for Translational Research in Cancer. "Traditionally when we have looked for genetic risk factors for, say, heart disease, we have assumed that the blood will tell us what's happening in the tissue. It now seems this is simply not the case” (Sciencedaily.com).
ReplyDeleteShubin describes the DNA in every cell of the human body as being exactly the same, yet something we have learned in AP Bio quite recently contradicts what Shubin believes about the DNA in our cells. The human immune system is a very complex network of cells that work together in order to destroy and keep track of the various pathogens that constantly attempt to invade the body. The immune system is able to recognize pathogens via antigens. Antigens “are large molecules, either proteins or polysaccharides. Some antigens, such as toxins secreted by bacteria, are released into the extracellular fluid. Many other antigens protrude from the surface of pathogens and other foreign cells” (Campbell 936). These antigens are recognized by “guardian” cells in the body called B cells, “the lymphocytes that complete their development in the bone marrow and become effector cells for the humoral immune response” (Campbell G-4). The plasma membrane of B cells has thousands upon thousands of very structural-specific antigen receptors, which recognize “just a small, accessible portion of an antigen that is called an epitope” (Campbell 937). Each B cell has differently structured antigen receptors on its membrane (unless it is signaled to multiply. Then B cells have identical receptors, but that is beside the point). During a phenomena called Immunoglobulin gene rearrangement, the genetic make up of mature B cells are slightly altered , and the slightly-altered genes are transcribed and translated into B cells that all have different antigen receptors: ” the amino acid sequence of the variable region account for the specificity of antigen receptors on lymphocytes” (Campbell 939). Each B cell that has a different antigen receptor is an “[exception] to the generalization that all body cells have exactly the same DNA” (Campbell 940).
Mikey Ling (mikeyling@ymail.com)
Although Shubin has made claim, “among every cell inside our bodies: all of them contain the exacty same DNA”, modern research has disproved this assumption in new scientific findings. Even if Shubin is correct in asserting the fact that different genes are active in pieces of DNA in different cells, this doesn’t necessarily correlate to identical DNA in a body.
ReplyDeleteA typical human cell expresses only about 20 percent of genes at any time. Different cell types are due to differential gene expression. Genes go through transcription that differentiates into a initial RNA transcript with the same sequence as the original gene. There, RNA splicing occurs, and introns are removed from the sequence. MRNA gets shipped out of the nucleus into the cytoplasm for protein synthesis to be translated.
Like Mikey has mentioned, research by Montreal scientists have revealed major genetic differences between blood and tissue cells. This has disproved the theory that every cell contains the same DNA. Except for cancer, samples of diseased tissue have been found tedious to take from living patients. The majority of samples used in experiments have been in the form in blood, but if blood and tissue didn’t match DNA-wise, the genome-wide association studies may be disproved.
Dr. Morris Schweitzer had been researching genetic causes of AAA (Abdominal aortic aneurysms). This usually strikes elderly Caucasion men who smoke, who have high blood pressure and cholesterol. In this rare vascular disease, tissue samples are removed from patients as part of the rehabilitation therapy. The scientists focused on a death-controlling gene of cells called BAK. They discovered critical differences between the BAK genes in blood and tissue cells coming from the same individuals who carried them. Differences in blood and tissue cells were also noticeable in healthy people.
This major discovery has started a chain of flaws in many scientific studies. For example, many scientists have assumed what happens in blood will reveal signs of what is happening in tissues. In the expensive genetic industry, blood samples had been drawn by many individuals to locate genes responsible for the genes. Saying that all cells have the same DNA would be contradictory to this recent finding. Results from previous studies have led to negligible conclusions, and this finding from an AAA patient may be a reason why. However, if mutations discovered in tissue cells predispose for AAA, it presents itself as a target for new therapies and practices.
Sources:
http://www.sciencedaily.com/releases/2009/07/090715131449.htm
http://dnawellnessinfo.com/dna-medicine/dna-cell-body-major-genetic-differences-blood-tissue-cells-revealed/
Your Inner Fish
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Kyle Kim, piece847@gmail.com