Crick's central dogma: Information flows in molecular biology and scientific discourse

Following the discovery of DNA structure by Watson and Crick (as well as Franklin, the crystallographer—I'm very partial to crystallographers!) in 1953, Crick went on to construct the central dogma, stating it in 1958 and restating it in 1970.

Why the restatement? Because during the period in-between, other people have come up with responses to it; evidently, Crick is dissatisfied with those articles that 'misunderstood' (Crick's own wording) the idea of central dogma.

To be fair, when I hear the term 'central dogma' in a Biology class, I was perplexed, too. The term 'dogma' belongs to philosophy, specifically epistemology, what is it doing here in a Biology class? If the Wikipedia page is to be believed, basically, Crick couldn't find a more awesome word. Hypothesis was taken by sequence hypothesis; framework probably sounds too ordinary; axiom probably sounds too mathematics-y; truth probably sounds too epistemological. Though considering that the central dogma describes universally almost every genetic system, it may be just a little exaggeration to call it universal genetic truth or something like that.  
Your Biology teacher probably explains the central dogma like this: In genetics, there are three important macromolecular carriers of information — DNA, RNA and proteins. DNA is inherited from your parents and sit in your cell nucleus (and mitochondria); DNA is replicated in cell division; DNA is transcribed to RNA. RNA (specifically, mRNA) is translated to proteins by the ribosomes. Central dogma is thus that framework in which the genetic information encoded in the DNA is finally expressed as proteins; it's a schematic of (genetic) information flow. Understand, class? And at this point, Crick would shake his head, raise his hand, and say, "If I may elaborate?"

And that is exactly what Crick wrote in the 1970 Nature paper. He would like to "explain why the term was originally introduced, its true meaning, and state why [he] think[s] that, properly understood, it is still an idea of fundamental importance."

The abstract:

The central dogma of molecular biology deals with the detailed residue-by-residue transfer of sequential information. It states that such information cannot be transferred from protein to either protein or nucleic acid.

Crick would like to point out that the central dogma is a negative statement, while the earlier sequence hypothesis is a positive statement. Thus it is intentionally limiting: the genetic information ends in protein and stays there—it's a cul-de-sac.

There are 3 other misunderstandings that Crick addressed, but I will leave it to you to read for yourself.

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This whole chronicle of central dogma—besides teaching us about information flow in molecular genetics—also says something about information flow in scientific discourse.

First, the way Crick formulated the central dogma is exemplary. Early molecular geneticists knew about DNA, RNA, and proteins; but how the genetic information flows among them was less elucidated. Crick and and his collaborators first assume that all possible information transfers exist (Figure 1, as reproduced below). 

From there, they took away the arrows. They realised that two-way arrows are improbable because forward transfers already involve complex machinery, so "it seemed unlikely that that this machinery could easily work backwards". Protein-to-protein was out, too, because of  "stereochemical reasons"; in other words, proteins that so depend on their 3D structure to function cannot simply transfer its sequential information, like the nucleic acids which possess base-pairing that make replication possible for the nucleic acid since it serves as its own template.
And if this whole process sounds like detective work, well, that's the other way round; reasoning is the basis for both science and detective work, in this case deduction in particular. I particularly like the way they dismantle the arrows that did not stand up to scrutiny, it's kind of Holmesian.
Second, the precise way Crick formulates the central dogma. Crick formulated that abstract with extraordinary precision that stood up to scrutiny. He said:

In looking back, I am struck not only by the brashness which alowed us to venture powerful statements of a very general nature, but also by the rather delicate discrimination used in selecting what statements to make. Time has shown that not everybody appreciated our restraint.

As explained in this paper, he intentionally focus on the protein and how information cannot get out from there. He remained "discreetly silent" about DNA and RNA, which he was not sure of. The astute reader may also point out about prions, aren't they protein-to-protein information transfer? Yes, but it's not "residue-by-residue transfer of sequential information", but transfer of 3D shape — Crick got that covered. And that is why scientists need to be unambiguous in their language: you may think that we of the ivory tower spoke in something akin to medieval Latin (a.k.a. academic writing), but we do need to transfer our information precisely, or else we will face... 

Third, misunderstandings. I don't know how it looked like in the 1960s, but nowadays information flow in scientific discourse seems to hit the cul-de-sac in bad journalism. Admittedly, there are a lot of papers in which the language is unnecessarily complex and only a few shine in clarity while maintaining precision. That may be one factor, but still, journalists need to put aside the sensationalism, explain our jargons, use a lot of proper analogies; in other words, transferring the information with high fidelity.

Bad journalism, like bad protein, generates more of itself. Both are not good for the brain.

Crick F (1970). Central dogma of molecular biology. Nature, 227 (5258), 561-3 PMID: 4913914

Punctilious

I've been wondering why I've never learned this stuff at school proper: the more exotic members of punctuation marks, such as en and em dashes, semicolon, colon, etc. I suspect the philosophy here is like the lion cub being pushed off the cliff: we the fledgling young writers are to fend off  in the real word of writing and out of the jungle of words we would have gained the arcane secret that a cub on a rite of passage has to find out for itself.

And indeed it is best to let soak in the ocean of words to let the subtleties percolate into the deepest of your subconscious, rather than superficially reading the rules from the guidebooks (don't get me started with Strunk and White's Elements of Style, that some linguists love to hate). That said, I will attempt to write a guide of sorts, the purpose being: 1) to crystallise and organise my own knowledge, and 2) to soften the landing for a cub I'm about to push off. Here goes.

Laughter

[I rewrote this composition from my student's 'O' Level EL Section 1 practice composition, keeping roughly the same plot]

The falling water droplets drummed a monotonous, reverberating rhythm in his mind. He absent-mindedly stared at the plates, endlessly scrubbing every inch of each plate and bowl, cleaning the spot over and over again. There was a curtain of somnolence veiling the muffled chuckle in the next room and his own wandering mind in the labyrinth of memories. Inevitably, his mind returned to her, as it had been, again, and again, and again.

He first met her in high school, when she transferred to his class. He didn’t talk much to her, since he was unnerved by her beauty and especially those lips that can launch a thousand ships: when she laughed, it came as a deep rumble in her throat, smoothly rolling out her tongue, quivering her lips a little, like deep-red blossoms in morning dew rattled by the gentle breeze. Her laughter; the pitch, the timbre, the accompanying dimples, the joy, the happiness of being that defined her so much, all these were etched in his heart. Still, his own laughter and happiness were absent. Oh, how he longed to imbue his own laughter on top of hers, making a resonant melody that would echo deep to the very fibre of existence; interweaving laughters, interlocking lips, interbraiding passions!

That was why when he coincidentally met her again in the university, taking the same class even, he was elated beyond measure. He was determined be close to her this time. He mustered the courage to utter her name after class, and she turned, her long hair making gentle waves, spiralling in the gentle springtime gust of wind. Her lips moved and out came his name, tenderly clear and resonant. He said he was surprised she still remembered him—instead of replying with words, she let out that laughter of childlike innocence and amusement and joy, that same dew-soaked field of blossoms as he knew before.

His quest of love afterwards was punctuated with ups and downs but gradually he was able to reach that harmonious chord—her happiness was his happiness and his was hers; her laughters that bewitched him so now was his, too. And to the duet choral of laughters was soon added a more harmonious depth, the ringing of the wedding bells, and thereafter, the healthy cry of a baby daughter.

Unfortunately, the sound of dissonance came. A malignant tissue was found in her breast and it already spread to her trachea. No one said the C-word but it thumped in everyone’s mind, unceasingly, ruthlessly. Her battery of chemotherapy left her weak; it robbed her of her luxuriant hair and cheerful voice and laughters, it drained her lips of colour, it sapped her will of living. It ultimately snatched her away from him. Now those etched impressions in his heart were raw wounds instead, gushing blood, seething immeasurable pain.

The rain suddenly stopped and the sunshine penetrated through the lethargic veil that clouded his mind. His young daughter just laughed upon seeing her favourite cartoon character. He saw his wife’s face mirrorred in this young life; her laughter echoes in her daughter’s — her eyes turned towards him, saying wordless “Daddy!” He hugged her young daughter as tightly as his arms would reach, and let out a wailing cry. 

Or perhaps it was laughter; it was indistinguishable.   

Castle in the sand

Today when I sit on that magical borderline
between grains of silicon dioxide and saltwater,
I dig out a little hole,
(kind of like an antlion's sandpit,
though there is a certain perversion that
the sand is the sand, but
the beach is not the desert)
I haven't so much as thought of digging a foundation
for a castle of sand, when
the waves sweep the sand level,
and the castle in the sand only becomes
the castle in the air.
But what struck me most wasn't the extinguished architecture,
but the fact that the waves gently, ferociously slapped everything even.
Castles of sand, houses, cities, happiness, sadness, anger,
well, people.
And the ancient voices doth spake:
Syrus: In the face of death all men are equal;
A Chinese sage: In the face of Truth, all are students.

(Me: In the face of tidal wave, run away.)

Frostian

Thanks to my overzealous notetaking as of late, I've found out that somehow I have inadvertently plagiarised Frost. See, I have had this fragmental verse written, unfinished, tentatively titled Saltsmith (though it really doesn't sit well with me), timestamped on March 15:

You are a salt statue

The undercurrent of the world is constantly eroding you

Step back, step back

Put the sign 'Under Construction'

And regain yourself

The passing sense of familiarity was tugging when I clipped from Robert Frost's Directive on May 7:

And if you’re lost enough to find yourself

By now, pull in your ladder road behind you

And put a sign up CLOSED to all but me.

Then make yourself at home.

Now I would like to think that I have perhaps tapped to that great ocean of Jungian collective knowledge, though I'm sure there are less romantic explanations to it. Lesson #1: Some things are better left romanticised; Lesson #2: I should not leave such crumbs of verses and dilly-dally until they grow stale and nobody wants to eat them anymore.