Tuesday, February 23, 2010

A brief guide to DNA sequencing Testing

Anyone who's made it through biology knows a bit about the structure of the double helix. Half of one is shown above, to illustrate its three components gives guide to DNA sequencing: its backbone is made up of alternating sugars (blue) and phosphates (red), and each sugar is linked to one of four bases (green). In this case, all of the bases shown are adenine (A), although they could be potentially be guanine (G), cytosine (C), or thymine (T). In the double helix, the bases undergo base pairing to partners on the opposite strand: A with T, C with G. When a cell divides and DNA needs to be replicated, the double helix is split, and enzymes called polymerases use each of the two halves as a template for an new opposing strand; the base pairing rules ensure that the copying is exact, except for rare errors.

In the animation shown at right, a string of T's is base paired with a partial complement of A's on an opposing strand. The DNA polymerase, which isn't shown, is able to add additional nucleotides (a sugar + base combination) under two conditions: they're in the "triphosphate" form, with three phosphate groups in a row, and they base pair successfully with the complementary strand. As the red highlight indicates, the polymerase causes the hydroxyl group (OH) at the end of the existing strand to react with the triphosphate, linking the two together as part of the growing chain are simple guide to guide to DNA sequencing. When that reaction is done, there's a new hydroxyl group ready to react, allowing the cycle to continue. By moving down the strand and repeating this reaction, a new molecule of DNA with a specific sequence is created.

DNA sequencing technology, which could help us detect genetic predispositions to illnesses, customize treatments accordingly, lead to the development of new energy sources, etc., is currently being used to either aion power leveling do long reads of hundreds of bases on genomes that have yet to be sequenced (see the news this week on the full sequencing of the domestic horse genome), or shorter reads that only align with a genome we have already sequenced .

There are only two more secrets to DNA sequencing. First, you need to make sure every polymerase starts copying in the same place guide to DNA sequencing, otherwise you'll have a collection of molecules with two randomly located ends. This part is easy, since DNA polymerases can only add nucleotides to an existing strand. So, researchers can "prime" the polymerase by seeding the reaction with a short DNA molecule that base pairs with a known sequences that's next to the one you want to determine.

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