Once upon a G phase dreary, while I pondered weak and weary,
Over many a quaint and curious volume of deoxy lore,
While I nodded, nearly napping, suddenly there came a tapping,
As of someone gently rapping, rapping at my helical core.
‘Tis some visitor,’ I muttered, ‘tapping at my helical core -
Tapping that I can't ignore.’
It was in the Homo genus, when the S phase was upon us,
Bonds of hydrogen, not so strong now, kept the base pairs
core to core.
Adenine twice paired to Thymine; Cytosine thrice paired to Guanine,
Helix to helix, purine to pyrimidine, mirroring forevermore.
Phosphodiester at the backbone holds this image forevermore,
But what else might lie in store?
'Twas a protein: DnaA, entering to separate
These two strands that seemingly had never been apart before.
Fearing loss of unification, suddenly I had a vision:
‘A polypeptide seeking entrance, entrance to my helical core -
Enterprising friendly enzyme seeking for my helical core -
This it is, and nothing more.’
A gap has formed, I am unwinding!
Enzymatic entities come rushing through my open door,
Oh! DNA helicases, moving to my secret places,
Working to unwind me, am I a prisoner of war?
Strand from strand pulled hand by hand, I'm sure not
Even though I was before.
Single stranded binding proteins attach themselves along my genes,
Providing for enzymes that hadn't been allowed before.
Topoisomerases release my strands from tight embraces,
Easing the tense supercoils that would have run along my core.
ATP is a requirement, needed to complete the chore,
Quoth the enzymes: ‘We want more!’
I'm exposed, it is so awkward, flippy floppy single stranded;
Longing sadly for the double stranded days of yore.
But what is this? I see a primer, RNA and nothing finer,
Moving up into my crotch, such a movement I deplore.
Ah! it stops, as luck would have it, anneals itself along my core,
Antiparallel and nothing more.
I need some healing; I need concealing,
Surely someone can discover salves to heal and cure my sore.
Not the deadly Amanita! I need DNA polymerase delta,
Affixing itself onto the primer, which otherwise I would ignore.
5′ to 3′ operation; covering up my open sore.
Quoth the enzyme, ‘I can do more!’
The enzyme works in such a hurry, causing me to fret and worry
Adenine shouldn't be with Guanine, these errors I do deplore.
Pol delta has a trick or two, surely it knows what to do.
Its exonuclease removes the base, 3′ to 5′ and nothing more.
Finding all its own mistakes, this enzyme is no sophomore.
Proofreading effects a speedy cure.
Lagging strand, so intermittent, fragments line my inner core.
RNA you are a stranger, you're in clear and present danger.
FEN and Ribonuclease cut, throwing litter on the floor.
Polymerase come fill the gaps! Gaps that no one should ignore.
Quoth the enzymes: ‘There is more’.
Leading strand you were so easy, lagging strand you make
Tiny nicks remain from enzymatic work that's come before.
3′ hydroxyl, 5′ phosphate, is separation your lasting fate?
DNA ligase to the rescue, ‘mind the gaps’, my paramour!
ATP is a requirement, love's not cheap, not anymore.
Quoth the enzymes: ‘There is no more!’
Where once was one, there now are two; Mitosis is the thing to do!
What beautiful twin daughters! Blessed with stellar Apgar scores.
Still, we left some stones unturnéd in our attempt to be
Telomerase is unexplored; it doesn't wish to be ignored,
Transcription and translation, too, lie upon a distant shore
Quoth the enzymes, ‘We said, no more!’
And the helix, never spoiling, still is coiling, still is coiling!
In the naked nuclear depths, the cytoplasm I deplore;
And hidden deep within my coils, information never spoils,
The splendid light of DNA shines on all I could not explain before.
There is grandeur in this view of life, this precious life we all adore,
Dividing still forevermore.