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What is the mass of my DNA?
July 14, 2007 8:52 PM   Subscribe

What is the total mass of the DNA in my body?

So, apparently, 97% of our DNA is noncoding or "junk". Assuming that noncoding=nonessential (a big assumption, I know, but bear with me), how much weight could an average person lose by undergoing a DNÆctomy™? Can I make a brazillion dollars from this idea?
posted by aliasless to Science & Nature (16 answers total) 2 users marked this as a favorite
 
Think as if you're one big cell, and use the ratios to estimate. What percentage of a cell;s mass is DNA? Almost nothing. I'd guess it's within a few orders of 0.00001%. You're mostly water, with a few hunks of calcium, and some trace other stuff.

If you got rid of the stuff that's not human, that'd be something way more significant. Did you know there are about ten times as many bacteria in the human body as human cells? Of course, most of it does nothing we know much about but is probably beneficial or essential in some way, so don't spend the money on a patent yet.
posted by cmiller at 9:06 PM on July 14, 2007


I think current estimates are that "junk" ranges from 80% to 90%. 97% is much too high a figure. (I don't know where the Wikipedia author got that number.)
posted by Steven C. Den Beste at 9:16 PM on July 14, 2007


I couldn't resist trying to figure this out. According to this page, each cell has about 6 picograms of DNA (6x 10^-12); According to this page there are as many as 10^14 cells in the human body (or maybe less by a couple of orders of magnitude). A little multiplication reveals that the total amount of DNA would then be about 600 grams, or roughly a pound. I will leave it to you to decide if overcoming all of the technical hurdles to accomplish your DNAEctomy will be worth it for that degree of potential weight loss.

I have no idea how reliable those numbers from the web are, but they sound reasonable and even if they are off by a lot, you still are not talking about a huge mass of DNA in the body.
posted by TedW at 9:46 PM on July 14, 2007 [1 favorite]


Well, given that we know the size of our genome (6*10^9 in diploid cells), we can work out the total weight per cell, which goes to 7.11*10^-15 kg of DNA per cell (from here). We will ignore mitochondria, as they are pretty much 100% coding, and vary in number per cell too much depending on the tissue.

An average estimate for cells in the human body is 10^14 eg. here.

Overall, this gives 7.11*10^-15 * 5*10^14 kg of DNA, or 0.7 Kg
posted by scodger at 9:53 PM on July 14, 2007


Of course, though 95 odd percent of DNA is "junk" we now know that a lot of it is still transcribed (see here), so I doubt I would be the first to volunteer for this treatment.

Of course, the last 5 in my above comment should be a 1
posted by scodger at 10:05 PM on July 14, 2007


The idea that some DNA is 'junk' because it is noncoding is rapidly, thankfully, being recognised as, pardon the technical term, complete hooey.
posted by docgonzo at 10:41 PM on July 14, 2007 [3 favorites]


Sorry to dishearten your idea; but nonessential is completely inappropriate. A lot of that DNA is used structurally as a way to stop the proteins from transcribing the DNA or other such ways of regulating proteins, etc. It may be junk in that it doesn't encode proteins, but we need it.
posted by uncballzer at 10:58 PM on July 14, 2007


What Unc said. A more detailed look at the human genome has shown that "junk" DNA may play a complicated and poorly understood role in the process of generating people and making them nice or tall, etc. I heard this on US National Public Radio so it's true.
posted by longsleeves at 11:53 PM on July 14, 2007


Note that this is not a very good idea from a weight loss point of view. Even if everything else about it was technically sound, it would only help the people who don't need it! People want to lose weight when they're fat. When you get fat, your fat cells don't multiply, they just get bigger. So they don't get any extra DNA! (I guess they have bigger skin and some other organs too, but fat is the dominating factor)
posted by aubilenon at 1:15 AM on July 15, 2007


Well this article from Genome Research cites that 97% figure as well. Although, just because we don't know what's going on in noncoding regions, doesn't mean they are nonfunctional. As shown by the fact that these regions are conserved between species.

And even if some region of your DNA is nonfunctional, all it might take is for there to be a one base mutation for it to become functional (we've seen examples of this in the evolutionary line). Are you going to cut out the part of your DNA that might mutate and give your child a superpower?

I'm not just talking about being one of the X-men (although that would be cool), but what about resistance to disease or artistic ability?
posted by bluefly at 5:44 AM on July 15, 2007


Drawing out from your question it would be interesting to make a list of non essential stuff that you could jettison from your body to quickly loose weight. Of course would would want to start out by getting liposuctioned to the max and perhaps reducing down the size of the old stomach a little. Then time to say goodbye to your appendix, wisdom teeth and probably a kidney. Finally you might not miss a hefty non-dominant arm nearly as much as you think you would.
posted by rongorongo at 6:21 AM on July 15, 2007


It might not be encoding DNA, but all of that DNA is extremely important because it is a buffer against harmful mutations. Having all of that non-encoding DNA around decreases the statistical chances for mutations hitting the 'important' DNA material during mitosis and environmental damage (mutagens).
posted by i_am_a_Jedi at 6:50 AM on July 15, 2007


The best estimates of human coding sequence as a fraction of the rest of the genome are greater than 98 percent.

And junk is really a misnomer—some of this stuff is verifiably essential for life. Cells without noncoding sequence would not be viable for a number of reasons, so you can't just get rid of all of it.

Having all of that non-encoding DNA around decreases the statistical chances for mutations hitting the 'important' DNA material during mitosis and environmental damage (mutagens).

No.

First, it's "non-coding," not "non-encoding."

Second, most types of mutations will occur at a certain rate per nucleotide, not per cell. If you expect one point mutation every 1000 nucleotides, if you have twice as much DNA, you'll just get twice as many mutations.
posted by grouse at 8:03 AM on July 15, 2007


Additionally, lopping off the non-coded telomeres at the ends of your chromosomes would make your DNA uncopiable, since polymerase needs something to hold on to while it reads the end of the coded section. So you'd be preventing cell replacement by mitosis. You'd enjoy being a pound lighter for a little while, then way too light as natural apoptosis kills your aging cells and, since they're no longer being replaced, over the course of a year or so you dwindle away to nothing.
posted by nicwolff at 8:15 AM on July 15, 2007


Excellent answers, thanks all.
posted by aliasless at 6:50 PM on July 15, 2007


Following that up with a coincidental personal note: I'm taking colchicine this evening for an acute attack of podagra, also known as gout. No-one is sure how colchicine cures gout, but you mustn't take too much of it, because it is poisonous, and the reason for its toxicity is similar to the effect I imagined above of deleting all your telomeres: it binds to the tubulin proteins from which your cells construct their cytoskeletons and in particular prevents the formation of the mitotic spindle that holds a cell's DNA in place while it's copied, and pulls the copies into the daughter cells as they split. So, too much colchicine, no mitosis, no replacements for dead cells, suffering and death.

Also, it makes you barf.

posted by nicwolff at 6:02 PM on July 20, 2007


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