The rockstar of biology: DNA

Let’s go back to the basics for a non-scary science topic: DNA.  Today is the anniversary of the publication of DNA’s structure, in 1953, so it’s on my mind.  The two most famous names associated with the discovery of the structure of DNA are Francis Crick and James Watson: they published the iconic paper detailing the double helix structure of DNA – it looks like a ladder that twists (see the image from their paper, below).  But they didn’t do it alone – in fact they couldn’t have discovered the structure of DNA without a couple of other people: Rosalind Franklin and Maurice Wilkins.  Both of their contributions (actual experimental work, unlike most of Watson and Crick’s contributions which were thought-exercises) proved that DNA existed as a helix, and without that knowledge, Watson and Crick couldn’t have figured out the structure of DNA.  There were actually three papers published 60 years ago today, all of which were instrumental in establishing that DNA exists as a double helix.

 Image

There are a couple of important features of DNA: it is made up of a negatively charged “backbone” (the ribbons on the edge of the ladder above) and bases that make up the “rungs” of the ladder.  There are four bases in DNA, adenine (A), thymine (T), guanosine (G) and cytosine (C).  These four bases contain essentially all of our genetic information.  The particular order in which they are “written” into the ladder determines what color your hair is, your predisposition to a variety of diseases, and possibly even has some impact on your personality.  Unless you have an identical twin, your genetic code is uniquely yours, and the billions of bases in each cell are not exactly like anyone else’s.

It’s important that our DNA exists in two strands, and a primary reason for this importance is that it makes copying the DNA relatively simple.  When your cells need to grow and split into two “daughter” cells, they need to copy your DNA, too – and hopefully with as little room for mistakes as possible.  No one wants to accidentally change a base and suddenly have an extra arm.  Fortunately, evolution came up with an elegant solution to the problem of error-free copying.  There are four bases in your DNA, but each base only ever “matches” to one other – T always matches with A and G always matches with C.  When your cells need to make an extra copy of your DNA, special proteins pull the two strands apart and then sequentially add the complement to whichever base is next, thereby allowing a relatively error-free method to replicate your DNA.  So if the strand reads “CATGA” then the copying machine knows to add “GTACT.”

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The strands are unzipped, then new bases are added to complement the existing strand, resulting in two strands, each of which contain one old and one new strand of DNA. (image from http://www.biologyjunction.com/nucleic_acids_.htm)

So those are the basics of arguably the greatest discovery in biology in the 1900s.  Since I’m a scientist and also a woman, and Rosalind Franklin never gets enough credit for her part in discovering the structure of DNA, I’ll leave you with the image of “photograph 51,” the humbly-named X-ray diffraction photo of DNA that precipitated the discovery of DNA’s structure, taken by Franklin in 1952.  (Sidenote: she died before the Nobel committee awarded the prize for discovering the structure of DNA in 1962, and they don’t award the Prize posthumously, so she isn’t listed with Watson, Crick, and Wilkins for the Nobel Prize in Physiology or Medicine – another reason she’s not as well-known).

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This is the data that really started it all. If you only recognize one “sciency” image, make it this one.

Want more?  Check out a more in-depth reference on DNA and DNA replication:
http://science.howstuffworks.com/life/cellular-microscopic/dna3.htm

Feeling brave/adventurous?  The original papers published by Watson&Crick, Wilkins, and Franklin are free online.  I suggest taking a look at Watson and Crick’s: it’s very short and pretty straight-forward in terms of vocabulary.  You might be surprised at how accessible it is compared to most science papers.  (Or at least I think it is – let me know if it’s wayyyy too far above the head of a non-scientist – that’s good to know for future reference.)
http://www.nature.com/nature/dna50/archive.html

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2 thoughts on “The rockstar of biology: DNA

  1. Pingback: The replication of DNA | The Journalist

  2. Pingback: How does sunshine make you tan? | Ease Into Science

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