There is an awful lot of DNA stuffed into every cell.Ben's blog on stars and grains of sand got me to thinking about DNA. How long would the DNA from every living thing on Earth stretch? Could we make it to the next star? The next galaxy? The end of the Universe?

Let's start out with people. Each human cell has around 6 feet of DNA. Let's say each human has around 10 trillion cells (this is actually a low ball estimate). This would mean that each person has around 60 trillion feet or around 10 billion miles of DNA inside of them.

The Earth is about 93 million miles away from the sun. So your DNA could stretch to the sun and back 61 times. That is one person’s DNA.

The best estimate I could find of the world’s population of people is around 6.7 billion. When we multiply 10 billion miles of DNA by 6.7 billion, we end up with, well, a really big number. Something like 6.7 X 10¹⁹ or 67 quintillion miles. That is too big a number so let’s convert this to light years.

A light year is around 6 X 10¹² miles. So all human DNA would stretch 11.2 million light years. The closest star to Earth (besides the sun) is around 4.2 light years. So we shoot way past that! The Andromeda galaxy is about 2.5 million light years away from us so human DNA could stretch there and back two or three times.

What if we add the rest of the DNA on the planet? It would obviously be much farther but it is hard to calculate because we don’t know how many plants, animals, bacteria, fungi, etc. there are on the planet. We also don’t have detailed information about every species on Earth.

Let's add bacteria to the mix. I decided on this because we know how many cells are in a bacterium—one.

One number I saw was that there are 5 X 10³⁰ bacteria on Earth. Bacterial DNA tends to be a lot smaller than human DNA so there will be less of it per cell. Let's say on average there is 4 million base pairs of DNA/bacterium (this number could be off by a very lot). This translates to around .05 inch of DNA per bacterium which means you need to scrape together around 1.3 million bacteria to get a mile of DNA. So all the bacteria in the world have about 3.5 X 10²⁴ miles of DNA.

How far is 3.5 X 10²⁴ miles of DNA? Well, it is about 640 billion light years of DNA. The end of the observable Universe is about 14 billion light years away. So if we stretched out bacterial DNA it would go to the end of the Universe and back around 23 times. Of course it would be incredibly thin and so actually doesn't take up much space in the Universe.

So that's just human and bacterial DNA. (Well, mostly bacterial since human is so piddly in comparison.) I haven't added all of the rest of the DNA out there. I'll leave that to you.

The author feeling cheekyLast Monday I finally took my show out on the road. At The Tech Museum I run hands on genetics programs for visitors. On Monday, we took them to Overfelt High School in San Jose.

And the students had a blast*. They got to take home 4X6 glossy pictures of their cheek cells like the one I posted here (that's my handsome cell). They got to use DNA from a crime scene to solve a murder. They got to make bacteria glow like a jellyfish. They got to spool their own DNA. And they got to learn what 1000-2000 bases of their DNA looks like.

For the most part they were genuinely excited and engaged in the activities. They learned about nuclei, dominant and recessive gene versions, why blood cells look different from nerve cells and lots more.

Some educators call this sort of thing "drive-by science." A scientist zooms in, wows the kids and then disappears. These educators feel that this sort of thing has little effect on learning science. I beg to differ.

This experience obviously can't replace classroom learning. But it can reinforce what they've already learned. And it can show them how exciting science really is (even if their textbooks have convinced them otherwise).

Nice theory, but is there any proof this sort of thing works? You betcha.

A new study out by the National Academies shows that this kind of "informal learning" greatly increases the retention time of the things people learn while in that environment. For example, these kids, having seen and taken a picture home with them of their own nuclei, will remember that a nucleus houses DNA longer than if they learn it in a textbook or lecture.

If the study is right, the students will also become more excited about science so they'll pursue it in the future. Especially if the teacher then does follow on activities to reinforce what they learned (which he will).

Hopefully the nine graduate students from Stanford's Department of Genetics and I did our part to get some kids wanting to learn more about science. Maybe we even got a few to imagine themselves as scientists. Not bad for a day's work.

* Quote from the students' teacher:

These are some of the adjectives my students used to describe their experience: "awesome", "cool", "fun"; and they don't use these very lightly when it comes to academic activities. Some of them were wondering if we are "going to do that again." They enjoyed not only the activities, but also the experience of interacting with young graduate students from Stanford. Some experiences that can be a matter of fact for us can be huge for some of these kids and have a dramatic impact on their lives.