The World’s Greatest Storyteller
Ft. the Golden Records and life’s information storage system
“Friends of space, how are you all? Have you eaten yet? Come visit us if you have time.” — One Kind Speaker of Amoy
It’s not very often that I feel calmed by the voice of Richard Dawkins. He’s an evolutionary biologist, the author of the eye-opening ‘Selfish Gene’, and also a described ‘militant atheist’ who has spent a lot of time debating religious leaders and creationists.
In a panel strictly for science storytelling, Dawkins shed his “rebellious” demeanor and delivered a pretty woah filled speech about what DNA tells us about the lives of living and extinct organisms.
You can watch the full video here, but underlying his story about mimicry in cuckoos was one of the wonder molecules of life, DNA, and what it can tell us about an organism’s history. In fact, the biological picture DNA has the potential to paint a picture so vivid, it might just claim the title of greatest storyteller.
Dawkins speech got me so excited about life’s personal messenger that I’ve decided to dedicate a whole post to it’s inner workings, starting with the basics, and ending with a potential message to extraterrestrial life.
What DNA is
Your genome is 200,000 page telephone book, expressed in the molecular language DNA. It is estimated that it would take a human working 8 hours a day, typing 60 words per minute, over 50 years to copy the human genome, and yet for the cells in your body, the whole replication process takes around an hour as enzymes work at 50 base pairs per second.
DNA is an organic molecule, meaning that it has more than two atoms within it (molecule) and contains the element Carbon (organic). The term ‘DNA’ is an acronym for a much longer, slightly complicated name: deoxyribonucleic acid.
The first part of that name refers to the molecule ‘deoxyribose’, a sugar molecule that attaches to one of 4 nitrogenous bases — adenine and guanine (called purines, because of their structure), and thymine and cytosine (called pyrimidines), to form a nucleoside.
Each nucleoside is then attached to a phosphate and evolves into a nucleotide. DNA obeys certain chemical rules, and so, adenine can only bond with thymine, and guanine can only bond with cytosine. As the nucleotides bond to each other, the two strands of DNA twist together into the familiar double helix we’re all well acquainted with.
The kind of bond formed between two strands of DNA is called a hydrogen bond — a notoriously weak bond that seems out of place in something as important as DNA! In fact, just heating a sample of DNA causes it to melts into two strands. But, a weak bond is essential for DNA replication, because the first step relies on unraveling the strands and separating them, as pictured above.
The splitting of strands doesn’t happen on it’s own. An enzyme (a catalytic protein that speeds up chemical reactions) called helicase spins the DNA to unravel it. In bacterial genomes, helicase can spin at ten thousand revolutions per minute (RPM).
As the strands separate, another enzyme called DNA polymerase can attach nucleotides to the ‘leading strand’ of DNA (called the 3' — pronounced, three prime, strand) and make a new, complete strand.
DNA polymerase can only work in the 3' to 5' direction, so the lagging strand (called the 5' — five prime, strand), needs a slightly different process to reach completion. Instead of being filled in continuously, new nucleotides are attached in fragments, named Okazaki fragments after their discoverer, and eventually connected together by the polymerase.
This process involves a lot more steps, and is a lot more complex, when it takes place in your body. However, these are some of the highlights of semiconservative replication: creating daughter DNA molecules that consist of one old and one new strand.
Most of your DNA is contained within the nucleus of your cells, and is fittingly referred to as ‘nuclear DNA’, but you also have a second, strangely foreign kind of DNA known as mitochondrial DNA (mtDNA). Mitochondria are organelles found only in eukaryotic cells, which means that bacteria and other prokaryotic cells convert energy without their assistance.
Mitochondria are incredibly important for human and animal cells — they convert the energy from consumed food to a form that cells can use for work. Most cells contain hundreds or thousands of mitochondria, each with it’s own membrane and DNA.
There are interesting hypotheses about how eukaryotic cells evolved to contain membrane bound structures, and perhaps the most interesting pertains to the existence of mtDNA. Mitochondria have reproductive material needed to make copies, the ability to make energy, and their own outer boundary that separates themselves from other organisms, just like bacterial cells. So, perhaps, they once existed on their own before being incorporated within a larger cell — a once independent being completely distinct from what we understand to be our own ‘human’ cells.
Mitochondria also help to regulate apoptosis, the ‘suicide’ of cells that helps ward off tumors and cancers, and use their genetic instructions to create the majority of the enzymes involved in the chemical reactions needed to convert energy.
Mitochondrial DNA gives us an amazing opportunity to track human ancestry. A fertilized egg consists of the mother’s and father’s nuclear DNA, but only the mother’s mtDNA. This fact has drawn a maternal line through all living humans. You can look back as long as you’d like into your family tree, and you’ll find that your nuclear instruction manual contains the markers of an equal number of males and females, but your mitochondrial instructions can be traced back to only one of those female ancestors.
Combined with evolutionary theory, this leads us to an incredible conclusion— an ancestor typically named ‘Mitochondrial Eve’, the most recent woman everyone living can trace their mtDNA back to. She wasn’t the first female Homo sapien, or the only woman who has contributed to today’s gene pool, or the only woman we are descended form. She is unique only because her mtDNA lineage has not yet been broken as it was other early human females.
Males have a similar heritage traced back to a ‘Y-chromosomal Adam’, who shares a similar role. He and Mitochondrial Eve, probably weren’t dating, but there is compelling evidence that suggests they lived in similar time periods.
What DNA really does
People have observed heredity in action for hundreds of years, perhaps even since their evolution. The molecular basis of heredity took a bit longer to uncover, but nearly every human has come to appreciate ‘receiving’ their appearance one of their parents. Many people have also encountered the child who doesn’t seem to resemble either parent at all, which leads scientists, and curious people, to wonder: why?
As we know now, DNA controls much of heredity. It’s job is mainly to code for proteins, macromolecules that make up much of your body. Your hair — it’s color and texture, your metabolism — the making and breaking of molecules for energy use and storage, your neurons — the cells that allow you to think and sense the world, all rely on proteins.
Inside the body, the code that leads to the creation of proteins is made up of nucleotides abbreviated with the letters A,C,T, and G. During a process called transcription, all of the T’s get turned into U’s (an acid base called Uracil), and deoxyribose becomes ribose, forming a new molecule called RNA. Intracellular structures called ribosomes can use that code to make proteins — a process called translation.
During translation, ribosomes are fed RNA three nucleotides (one codon) at a time. As the ribosome senses each codon, a corresponding amino acid attaches to another portion of the ribosome. This process continues until a sequence called a ‘stop codon’ enters the ribosome and the long string of amino acids is detached. This process is shown in greater detail here:
Amino acids are the building blocks of proteins, and in the later stages of translation, chains of amino acids fold and combine to form 3 dimensional proteins with specialized functions.
The fact that DNA codes for proteins is part of the reason it can be challenging to answer certain questions, like: what gene controls my intelligence? The answer is likely several genes combined with environment, psychology, and bringing. But, another function of DNA adds still another level of complexity to the subject.
Not all regions (called loci) of the human genome are genes that get turned into proteins. In fact, early scientists came to the conclusion that 97% of the human genome consisted of ‘junk DNA’ with no known function. Your DNA is composed of introns (non-coding) and exons (coding), and exons are exceedingly rare. Only 1% of some 3 billion letters that make up your genome will eventually be translated into proteins.
Why functions are hard to find
The study of genetics has been around for a while, but in the late 20th and early 21st centuries, genomic technologies were reaching new heights. The challenge for these pioneering biologists was to read and decipher a book written in the cell’s native language. In 1995, the first ever genome from a free living organism, that of a bacterium Haemophilus influenza, was completely sequenced. Not long after, biologists braved the human genome which revolutionized medical technologies.
After sequencing, there needs to be some way to interpret the billions of letters in human cells. Enter functional analysis, a process that attempts to make sense of all those letters. In modern practice, this can be done by searching through large databases of genes that already have been transcribed and translated, and seeing how closely your sequences align with those genes. The NCBI (National Center for Biotechnology Information) has created tools like BLAST to align sequences to those found in their databases.
If your sequences align very well, it can correspond to the name of a protein (although those names have varying degrees of specificity). Genome annotation further attempts to identify specific structures or functions and can return promising results. Unfortunately, a description like ‘heat shock protein 4’, might not immediately help you answer a large question like: what gene controls hair color? The answer, we can infer, is many genes all coding for a different protein, combined with non coding regulators.
The process of genome annotation, and finding functions and structures, is another process whole books are dedicated to! If you’re looking for more detail, I’ll leave additional resources in the citations.
Information storage in animals
For the vast majority of life on Earth, DNA is the sole and primary method of storytelling. Not only can an organisms characteristics tell others important information about themselves (in regards to mating, toxicity, etc), but when interpreted by human technologies, we can often understand the bigger picture — things like morphology, and changes to populations.
Presently, we can even generate whole, 3D faces based on DNA with a decent degree of accuracy. Perhaps someday, genomic technologies will advance to extrapolate whole environments just from the chemical codes of the organisms that once lived there.
We are the only species, as Carl Sagan once pointed out, that stores information outside of our own bodies. We store it in books, articles, computer files, artwork, pictures, sound recordings — everywhere we can! And that speed of information sharing has, no doubt, contributed to the advancement of humans in everything from technology, science, history, philosophy, even language.
While its a bit more anthropocentric than I care to be (bacteriocentricity seems far more revealing), it is true that human’s external information storage system is incredibly important… at least to us. That’s why when Ann Druyan, a writer and producer, and Sagan, her astrobiologist husband, decided to send a bit of humanity out into space in the form of golden records — with the hopeful assumption that, aboard the Voyager spacecraft, they would one day be found by intelligent life. That is to say, life who’s intelligence is comparable to or greater than our own.
The idea is that intelligent life forms would receive the records, which are currently 40 years (over 12 and 10 billion miles, and moving quickly) away from Earth, and follow illustrated instructions to build a record player. They’d then see images of human forms, food, animals, homes, and water, and hear the music of Bach, Australian aboriginals, and — if they fancy Rock n’ Roll over Classical, Chuck Berry.
The Golden Records contain greetings from Earth in 55 languages, including one of my favorites, penned in the Min dialect Amoy. Translated in English, it reads:
“Friends of space, how are you all? Have you eaten yet? Come visit us if you have time.”
While it’s unlikely anyone reading this will ever get to see the fruition of the Golden Records, they will continue journey through space and are expected to be playable for a billion years. If we don’t kill ourselves off, perhaps our descendants will see extraterrestrials extending an olive branch (or a ray gun) our way.
The goal of the records was to give extraterrestrials a brief introduction to humankind and the life forms of Earth. The Voyagers were sent on their way in 1977, the same year the first viral genome was sequence, but long before the development of current bioinformatic software.
Given what we can understand and interpret about a species based on it’s genetic code, perhaps the golden records should’ve contained a manuscript of DNA instead.
Don’t take my word for it! View the full list of citations here.
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Hi! I’m flagellate. When I’m not swimming in agar, or writing about my favorite microbes, you can find me making up stories about the end of the world, and helping science get funded.
