Can a sewing machine stitch together DNA?

If you've read How Cells Work, you know that our cells divide. It's how we maintain ourselves, grow and repair injuries. If you're an adult, you might be surprised to learn that 2 million cells in your bone marrow divide every second to keep enough red blo­od cells in your blood [source: Becker].

Every one of your new bone marrow cells looks and acts just like the old. Why? Because they have the same genetic instructions in the form of DNA. The old cells take great pains to copy their DNA and hand it down to the new cells. You might think it happens like copying on a copy machine, where old cells keep their old DNA, and new cells get new DNA. But what happens instead is more like sewing.

If you could look inside one of your old bone marrow cells, you would see that DNA is made of two strands "sewn" together by chemical bonds. When the cell divides, a "scissors" enzyme, called helicase, rips apart the two strands. Like little pins, binding proteins hold the two strands apart. DNA polymerase, an enzyme that's like the best tailor in the city, follows the template of the old strands and sews in a new strand made from building blocks in the cell. After the cells split, each has "tailored" DNA made of a new and an old strand. DNA replication is an amazing and intricate process that you can learn about in How DNA Works.

Now that we know how our cells capably and constantly complete this process, let's see how aspiring seamstress scientists compare.

It may not happen on a Singer sewing machine complete with foot pedal, but scientists often "sew" pieces of one organism's DNA into another's. The result is called recombinant or "chimeric" DNA, named after chimeras, the mythical creatures that are part lion, part goat and part snake.

Often scientists will insert human DNA into bacterial or yeast DNA [source: Tamarin]. With a little extra engineering, bacteria and yeast can take up the recombined DNA and follow the instructions as if nothing happened. The organisms then make human proteins. The process has many applications in research, industry and medicine. Right now, bacteria and yeast are making huge amounts of human insulin, which is used to treat diabetics [sources: Cold Spring Harbor National Laboratory, Eli Lilly].

In addition to sewing DNA, scientists are also straightening it. Our DNA is coiled, coiled, coiled. To study it, you need to straighten it. One popular way is to attach a bead to either end of the DNA, pick up the beads with a laser beam and gently pull the beads apart, says Patrick Doyle, a chemical engineering professor at MIT.

What in the world do scientists do with straightened DNA? In How Epigenetics Works, you'll learn that the outside world, and even the world of our parents, can influence which of the instructions in our genes our body follows. The environment can "talk" to our cells through molecules that direct the reading of our DNA. By straightening DNA, or at least uncoiling it a bit, scientists can study these modifications. They might watch proteins attach chemicals to our DNA or turn genes on and off. Another use of the bead trick is testing whether drugs meant to bind to DNA will work. Scientists can sense whether the drug has bound to DNA by measuring changes in the tension of the coil [source: Doyle].

­

If what you want is machines, yes -- researchers are building small devices that don't sew but do straighten DNA. Doyle is making one the size of a postage stamp that sends DNA in a stream of liquid through a funnel, straightening it. It could become part of an environmental sensor that sucks in organisms from the air and detects dangerous microbes by their DNA sequence. Would you like to put Doyle's device in your basement, beside your sewing machine? Not so fast: It's not for sale, and it costs more than $10,000 to make.

But the device that wins the prize for somewhat resembling a DNA sewing machine lives in the labs at Kyoto University. A little larger than a credit card, it also uses liquid to push DNA around on a chip. In a 2008 paper published in the journal Lab on a Chip, the researchers showed they could unfurl a wad of yeast chromosomes and, using flowing liquid and a little hook, peel them apart and stick them to posts. Then, letting the chromosomes wad up again, they wound them around two spools [source: Terao]. The hooks and spools measure in the millionths of a meter -- thousands could fit on the head of a pin. While the device hasn't been tested on human DNA, Doyle says the technical display of manhandling long, easily breakable DNA without breaking it was "pretty cool." "Theirs was a clever way of grabbing any old big strand of DNA and moving it around," he says.

So you can't stitch DNA together with a conventional sewing machine, but scientists can manipulate DNA for our benefit. Keep reading to see what else scientists are up to in the field of genetics.