Science As We Know It

Last week, on the 25^th of April, the commemoration of the DNA Day took place. Celebrated on this day, the date when, in 1953, Rosalind Franklin, James Watson, Francis Crick, Maurice Wilkins, and their collaborators published their studies about the structure of – you guessed it – DNA.

In line with this, and given that we previously talked about the different structures found in a cell, we thought it would be a great opportunity to talk more about this amazing molecule containing pretty much all our information. (Yes, even more than your Instagram page.)

DNA stands for DeoxyriboNucleic Acid (bless you!), and it is famously shaped like a double helix of two strands that revolve around each other. Within this twisted ladder-like structure, you can find the information for the functioning, development, and reproduction of every known live organism.

“How so?” you ask.

Well, if you think that the four letters that form life are L, I, F, and E, you are mistaken. They are actually A, T, G, and C. And no, I am not having a stroke. Here’s the thing, these long strands of the DNA molecule (a polymer) are composed of smaller pieces (monomers). These smaller molecules are called nucleotides, and there are four of them: adenine [A], thymine [T], guanine [G], and cytosine [C]. 

The sequence of these nucleotides is in itself a real code for the production of proteins, the biomolecules that constitute pretty much everything in a cell. So, each sequence of 3 nucleotides means a specific part of a protein, called an aminoacid: ATT means one aminoacid, GAC means another, and so on… You basically have a library of all the proteins your cells can produce being encoded in this 4-letter alphabet!

Thanks to its double-helix coil shape, it can turn around and around on itself so it can take up the least amount of space possible. To give you an idea, if we completely stretched out the DNA of one single individual human cell, it would measure approximately 2 meters. But the nucleus of the cell, where it is contained, only measures about 6 micrometers in diameter. (If you think Marie Kondo was the master of space optimization and organization, think twice!)

The smart thing about it is that the important parts of the long DNA molecule are specifically uncoiled, according to the needs. If a region of DNA is needed to be “read” for a specific protein, it unfolds and opens up that area in particular. And then it “closes again” when not needed anymore. These very long fibers of DNA, when condensed and packaged, form the chromosomes. Which, precisely when they are so packed, can be easily visualized under a light microscope. 

DNA is not only very efficient for information storing but also for information proliferation. When preparing for cell division, the entirety of DNA is replicated: the helix shape uncoils, both strands separate and new nucleotide building blocks come to “copy” each one of the strands, generating two. These will then form two sets of chromosomes, which can be split between the two new cells that form after division.

And here it is. Now you know why the forensics TV shows enjoy DNA so much. It is a biological trace that is different for every human that exists or ever existed. And all of this is encoded in only 4 letters.

So, hopefully, this article made you think twice before committing a crime.

Happy DNA day!