A few days ago my daughter, Jenna (12), came into my office and asked why I have something on my desk that looks like a toy, with all it’s bright, solid-colored plastic and rubber pieces. Perhaps she thought it was a bad attempt at art and was questioning my poor taste. Regardless, the conversation was on and I was eager to explain just what is the thing on my desk. Deoxyribonucleic acid, I told her, is perhaps the most amazing thing there is, to which she retorted in usual Jenna-fashion, “What about the universe?” Well, yes, The Universe is the one thing I had considered to be even more amazing than DNA, but that’s about it. This molecule, with its marvelous structure, is not only responsible for all of the diversity of life, but is the recipe for all the complexities of every living organism, including herself.
I’ve long known the basics of the DNA molecule: a double helix consisting of two complimentary chains of bases connected to a backbone that unzips and meticulously copies itself and is contained in every cell of our bodies. The structure of DNA was first published in the journal Nature on April 25, 1953 (click the thumbnail on the right to read the original paper). That single-page paper is extraordinary in its simplicity and explanatory power. As Matt Ridley writes on The Edge, “Never has a mystery seemed more baffling in the morning and an explanation more obvious in the afternoon.”
The marvel of this molecule cannot be overstated. The fidelity of replication means that the progeny of hamsters are hamsters and dandelions dandelions. The fascinating mechanisms of embryology are only understood through the lens of DNA. The random mutations in the billions of base pairs give rise to genetic diversity in a population and is the engine on which Darwin’s natural selection operates. Life on this planet is, quite actually, a product of the deoxyribonucleic acid molecule.
So, yeah, it’s cool stuff. I wanted a model of it. Who wouldn’t? After a bit of research on Amazon I found Molymod’s 22-nucleotide long model, and placed my order. I didn’t expect to learn much more from the model than I had already known. Boy was I wrong. Its parts are not only of very high quality and craftsmanship, but it demonstrates several attributes of the molecule that are not apparent from the assembled model. The nucleobases are connected to their compliments with either two or three pegs, depending on the number of hydrogen bonds. Likewise, the phosphate-deoxyribose chains have a direction, as they each have one hole and one peg. So the two backbones can be assembled in opposite directions, as is the case in the actual molecule. Continuing with the educational value of the model, the deoxyribose (sugars) are five-sided (pentose). The model correctly spirals 360 degrees in the anti-clockwise direction for every ten base pairs. The major and minor grooves are also easily visible in the model.
Putting the model together certainly piqued my curiosity to learn even more about DNA. It’s quite beautiful in its structure. And, as per usual, the more I learned the more fascinated I became. Poor Jenna. She patiently allowed me to elucidate each part of the model and describe its purpose and function. Then she walked away, seemingly non-plussed.
Notice in the picture of the model’s parts below the hydrogen bond pegs on each of the bases and the direction of the deoyxribose-phosphate chain? Because the diameters of the holes and pegs differ in the thymine and adenine bases particularly, every nucleobase can only possibly be connected with its compliment, assuring an extremely high degree of fidelity in replication.
This photo shows the big difference in the widths of the minor and major grooves, as well as the anti-clockwise double helix shape, the perpendicular orientation of the nucleotide bases, and the alternating sequence of phosphates and pentose sugars that constitute the backbone.
When looking at the model obliquely in the longitudinal direction, the bases nearly disappear and all one sees is the deoxyribose-phosphate backbone of the molecule.
I’ve included an illustration for the “big picture” of DNA below from the National Institute of Health’s National Human Genome Research Institute website. I encourage you to unravel this magnificent molecule and explore its simplicity, elegance, and power. It is most awe-inspiring and remarkable.
If dissecting the molecule to understand its intricate parts and functional elegance doesn’t completely blow you away and fill you with wonder, let this TED video blow your mind. You’re welcome.