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Name: Hasib
Status: Other
Grade:  Other
Location: ND
Country: United States
Date: July 2008


Question:
How do you determine the molecular weight of DNA? In its simplest form, what would that weight be?



Replies:
The most common way to determine the Mw of DNA is to run what's called a 'gel electrophoresis'. The two main words in this are 'gel' and 'electro' -- the 'gel' is a porous material that DNA flows slowly through. The 'electro' refers to the fact that DNA is charged, so an electric field can be used to make it move through the gel. The smallest DNA moves the fastest through the gel, so over time, DNA of different lengths is separated. 'Gel electrophoresis' is covered many times over all over the web, so I won't repeat the details here. You can do an internet search to find out all the details you want (and more). There are other ways to measure DNA Mw as well, but that's the most common and easiest.

As for DNA's "simplest form", that's a little more difficult to answer. DNA is a polymer, which means it is a long chain of similar sub-units. In DNA, the units are called 'nucleotides'. However, a single nucleotide isn't really the 'simplest form' of DNA because a single nucleotide doesn't really function as 'DNA'. It takes at least several nucleotides to have any biological meaning. So it's not that easy to answer what the 'minimum' molecular weight is. A single nucleotide Mw is around 250Da (it depends on which nucleotide -- there are several options), but DNA strands can be millions of nucleotides long. And, DNA can be double-stranded -- in other words, two strands attach to each other and wrap around each other. This is the famous 'double-helix' structure of DNA.

Perhaps you could respond and let me know why you are interested in its molecular weight I can give a more contextual and useful answer to your question.

Hope this helps,
Burr


There are many different ways to determine the molecular weight of DNA. Use a search engine like Google to learn about them. Every base pair in a DNA molecule contributes about 600 Daltons (1 Dalton = 1 atomic mass unit) to the molecular weight of a DNA molecule. If the DNA molecule of E. coli contains about 3 million base pairs, it's molecular weight would be around 1.8 x 109 Daltons. Molecular weight is the sum of the atomic weights of the constituent atoms.

Ron Baker, Ph.D.



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