Tuesday, 6 December 2011

Mommy, Where Does Blood Come From?

With the recent rise of the vampire star in popular culture, this scientist thinks we’ve all been seeing a little more blood in everything from movies, to television, to magazine ads. While it might not be immediately apparent from these corn-syrup-and-food-colouring imitations, our blood is pretty complex stuff. Like so much of our bodies, what seems like a simple (if slightly goopy) liquid is really a mixture of different types of cells and substances. Also like much of the rest of us, the makeup of this serological soup needs to be closely regulated to keep us alive. When it comes to controlling the composition of our bodies, enzymes have the gene-wrangling power that places them squarely in the drivers seat.

            If CSI: Miami has taught me anything, it’s that sunglasses are required to investigate crimes, and each person has unique DNA. In fact, each cell in your body carries the exact same DNA sequence, the same genetic code. So how do some cells end up as heart muscle, and some as fingernail, and some as bone marrow? If all of the DNA is the same, how can it hold information for making so many different kinds of cells? What makes different kinds of cells different isn’t their DNA, but the proteins that exist in that cell. Proteins are made by decoding specific parts of the DNA, so the body controls what cells are what by regulating what pieces of the DNA get decoded to make protein. It’s kind of like having a whole recipe book with many recipes that could make up many meals. If you want a pancake and poached egg breakfast, you use those specific recipes to come up with the desired end product.

            To control what proteins get made in each cell, we control which recipes are available to the chef. Our DNA isn’t just crammed willy-nilly into our cells, but has a defined structure in which it is wound up very tightly. There are proteins called histones that the DNA folds around to help condense it into a smaller space. The DNA itself, as well as the histones, can be modified by attaching specific chemical groups. In this way, the DNA can be effectively labeled with respect to which proteins should and shouldn’t be made in that cell. This labeling doesn’t happen on it’s own, however. There are specific enzymes that attach and detach these groups from our genetic material, thus controlling which genes get made into protein (expressed) or are wound up too tightly to be accessed (repressed).

            One of the chemical groups enzymes attach to DNA is the methyl group: one carbon atom attached to three hydrogen atoms. A team of researchers in Texas recentlyinvestigated what would happen if an enzyme responsible for methyl-labeling was removed from stem cells in the bone marrow. Normally, these cells are responsible for morphing into all the different types of cells that make up our blood and bone marrow, in addition to making more stem cells. When this DNA-labeling enzyme was absent, the cell made the wrong proteins at the wrong times and could not make functional blood cells. Their experiment showed that DNA labeling by this enzyme is a key part of how the body produces the blood cells we need to live.

None of us could survive if we only made one type of cell. It’s our bodies’ ability to pick and choose the right recipes for the right occasion that results in our different body parts and organs. With enzymes playing such a key role, maybe the vampires are just missing an enzyme they need to make their own blood. Human blood, a vampire’s complete breakfast.