History of DNA: Past, Present, and Future

DNA — deoxyribonucleic acid — is the molecule we associate with life on Earth: it appears to be crucial for anything to be confidently called "alive".

As for everything related to life, however, things are not straightforward. Even though the connection between DNA and life is clear, scientist don't have (and possibly will never, as this is one of the most challenging questions to answer) a unique answer to when this connection formed: it's generally accepted that once cells started storing genetic information in the DNA molecule, life had either just appeared, or had started briefly before that moment (using, for example, RNA, a related molecule). And we are not even sure if DNA-life is the only life on this planet. Have you heard of the shadow biosphere theory?

Only a few decades ago, humanity gained insight into this billion-year-old connection with the discovery of DNA. All the progress of our knowledge about it is nothing but an instant compared to the timescale of the existence of this molecule. More discoveries lie ahead, either on Earth or on other planets.

Let's explore some of the history of DNA and learn more about this fascinating double helix! In this article, you'll read about:

• The ancient history of DNA;
• The breakthrough DNA discovery by Watson and Crick… and Franklin;
• What lies ahead: genetic engineering, and more!

DNA, initialism for deoxyribonucleic acid, is a rather complex molecule found in the nucleus of the cells of living beings. We'll discuss its structure in a moment; for now, it's sufficient to know that it enables the storage of massive amounts of information.

This information constitutes the blueprint to build an organism, the instructions needed to produce the materials, how to arrange them, and all additional information on characteristics and features. DNA decides if you will be an E. coli bacteria, a Triceratops, a grapefruit-sized dovekie, or a human. If you are a human, your DNA will determine whether you are a woman or a man, as well as your eye color, hair color, and other physical characteristics.

Life is complex. Even simple, single-celled bacteria are made of multiple components that interact in a complicated way if, and only if, everything is built to a T. For example, E. coli contains approximately 0.6 MB of data — it may not sound much, but it's enough to store 25 times the US Constitution.

How does DNA store this information? Let's take a look at the structure of this molecule. If you had a powerful enough microscope, and you looked at a section of DNA filament, you'd initially notice an elegant double helix structure.

A helix is a geometrical figure that you can imagine as being generated by a point on a propeller as it moves forward. The thread on a screw is a helix.

DNA's older sister, RNA (ribonucleic acid), is a single helix molecule.

If you take the same propeller as before, and consider a point and the point diametrically opposite, and trace their paths as they move forward, you obtain a double helix.

In DNA, the double helix we have just drawn is what is technically named sugar-phosphate backbone, and it repeats uniformly over the entire length of the molecule. On the inside of the double helix, molecules called nucleobases extend and pair from opposite sides of the backbone, in a shape that neatly reminds us of a spiral staircase.

There are four possible bases, marked with four capital letters:

• A for adenine;
• T for thymine;
• G for guanine; and
• C for cytosine.

These pair two-by-two according, forming two possible pairs:

• Adenine with thymine (A-T); and
• Guanine with cytosine (C-G).

This effectively creates two possible "steps" in our staircase, and as 0s and 1s in a binary code, the way these pairs alternate allows the DNA molecule to store information.

That's all we need to know about the structure of this fascinating molecule: let's find out next about the origin of DNA!

Let's cut to the chase: we don't know precisely where, when, and how DNA originated. However, we are fairly certain that DNA originates from RNA as a more stable nucleic acid molecule, but we only have hypotheses about the origin of the RNA molecule. Nucleic acids possibly arose with RNA (as it has a somewhat older structure than DNA) around 4.2 billion years ago, but many doors remain open about how RNA came to be.

The hypotheses range from chemistry in the deep ocean, to asteroid impacts catalyzing the proper reaction, passing from more enticing — albeit imaginative — ideas like panspermia, according to which life's building blocks originated somewhere else in space, hitched a ride on some rock, and crash-landed on the young Earth.

Regardless of its origin, DNA is only but a component of a more complex dance (also involving RNA and proteins: you can learn more by using our DNA to MRNA converter or reading this article about the transcription process) where every part is needed — and is meaningless alone. It is likely that a rudimentary mechanism connecting nucleic acids to life originated before DNA; this is part of the so-called RNA world hypothesis, a vision of an ancient Earth where life began its expansion using simpler molecules.

For around four billion years, DNA conducted a quiet life — pun intended — orchestrating evolution, defining every living being that walked, flew, or swam (and everything in between). This peaceful anonymity was disrupted by a series of groundbreaking discoveries that allowed humans to peek all the way down to the molecules that make up life.

In the 19th century, Mendel laid the basis of genetics, the idea that traits (like the color of your eyes) are inherited according to how single genes — related to that trait — pass from parents to offspring.

Mendel's observations were at a "human scale", made by carefully breeding peas and observing generation after generation. At the turn of the century, scientists began relating genetics to parts of the cell: first the nucleus, then chromosomes within it.

The culminating discovery was made by Sturtevantin 1913, when he proved that genes are arranged linearly (one after the other) on chromosomes. The doors to the understanding of DNA's structure and role were open.

Around the same time, chemists were learning about the composition of what was inside the nucleus. By the beginning of the 20th century, bases were known, and not long after, evidence emerged that bases are paired in specific ways.

What was missing was a clear understanding of how bases and the sugar-phosphate backbone were arranged, and how this mattered in the way DNA works as the blueprint for an organism. DNA is small, its width oscillating between 1 nm and 2 nm (a nanometer, nm, is a billionth of a meter), just about 20 atoms wide. Even with today's TEM (transmission electron microscopes, the most powerful "conventional" microscopes available), it is barely possible to observe grooves in it. However, in the mid-20th century, a combination of wit and experience allowed science to discern that structure.

Enter Watson and Crick.

The first image of DNA with a recognizable structure is from 2012: scientists captured it using an electron microscope. This is almost sixty years after we discovered the structure of this molecule!

The year 1951 marks the beginning of their collaboration. Their imagination and understanding of the chemistry of DNA will allow them, in a couple of years, to reliably understand and model the structure of the molecule. Some information was still missing to enable them to do so.

At the same time, Rosalind Franklin was an expert in X-ray diffraction, and was working together with other researchers on the DNA molecule.

DNA can form something akin to a crystal, on which scientists can perform X-ray diffraction. That's what Raymond Gosling, under the direction of Rosalind Franklin, did, producing the famous Photo 51.

Photo 51 was then passed, without Franklin's consent, to Watson and Crick, who used it to corroborate the model they were developing. According to the "Cambridge model", DNA is a double helix structure where pairs of bases face inward, while the outside is composed of a structure of sugar and phosphates.

This discovery marked a turning point in the study of genetics. It was now possible to explain the mechanism by which DNA encodes information, and how this information is read and used to produce materials needed for life.

For the discovery of DNA's structure, Watson and Crick won the Nobel Prize in Physiology or Medicine in 1962, alongside Wilkins (Franklin's colleague, with whom she had a complicated dynamic). Franklin had passed a few years before due to cancer.

Her effort and brilliance, which led her nanometers away from visualizing the structure of DNA, went largely unrecognized until a few years ago, when the history of the discovery of the DNA structure was revisited. Tales of interactions, contrasting personalities, and what Nature defined the dysfunctional DNA's team resurfaced, and today Franklin finally, albeit far too late, is regarded as one of the fundamental people that contributed to the development of genetics.

Once the structure of DNA became known and was shortly thereafter accepted by the scientific community, researchers began to develop an entirely new branch of studies revolving around this newfound knowledge. It was the dawn of modern genetics.

Broadly speaking, two main areas of interest can be found in the field:

• Genetic sequencing, which involves "reading" the genetic code; and
• Genetic engineering, that involves modifying existing genetic material or creating new strands of it.

Sequencing is fundamental to understanding the role of genes, and even more so, the difference between individuals. Observing the differences between genetic codes allows us to determine how closely two species are related, for example.

Reading was not enough, and by the early 1970s, researchers had already developed techniques that allowed for the injection of DNA from one organism into another. In 1973, the first genetically engineered animal, a mouse, was born.

From then on, scientists learnt how to create GMOs (genetically modified organisms) to benefit agriculture (by developing strong disease resistance) and farming; in the 21st century, CRISPR, an innovative engineering technique, allowed for the controversial modification of the genetic material of human embryos in China.

Genetic engineering has an immense potential, but is also hard to understand and explain to the public, and invokes thoughts of uncontrolled modifications. Its power and the consequence of its inconsiderate use are immortalized in Jurassic Park by Michael Crichton. Demonizing this field of science, while understandable, is irrational: as with many other high-risk technologies, it is subject to tight controls and restrictions (much like nuclear technology, which, while risky, has been developed into an extremely robust and safe).

Bad actors can, and will, emerge; the coordinated effort of institutions and science is responsible for suppressing these malicious developments. From the side of the public, trust in the good intentions of such institutions is required: otherwise, the effort doubles, and progress is sacrificed.