The following narrative presents a fictional dialogue between two historical figures regarding the invention of polymerase chain reaction (PCR)—a revolutionary technique that has transformed the fields of biology, medicine, and biotechnology, enabling us to identify COVID infections.

The conversation…

"I’ve got it! I’ve got it!! Jenn, I’ve figured it out!"

The vehicle swerves along the winding mountain road as Kary enthusiastically pounds his fists against the steering wheel. The headlights flicker across the towering redwoods, casting shadows that seem to dance anxiously in the dark.

Startled, his girlfriend, Jennifer Barnett, clutches the armrests. "What’s going on? What have you discovered?"

"I can amplify DNA! I can produce loads of it—it's a chain reaction! Wooooo!"

"Calm down or we’re going to crash! Are you on something again?"

It’s 1983, and Kary B. Mullis, Ph.D., is an exceptional biochemist and research director at Cetus Corporation, one of the pioneering biotech firms in the U.S., specializing in the production of short synthetic DNA fragments.

Mullis has successfully streamlined the process of creating these short DNAs, leading to an excess of free time for him and his talented team of Ph.D. chemists. Concerned about potential layoffs, he seeks innovative applications for oligonucleotides, the short DNA strands.

"I only took one hit of acid, Jenn, so I’m totally fine! The ideas lighting up in my mind are incredible, like a laser show in a planetarium. I wish you could see what I see!"

Jennifer glances at Kary with skepticism.

"Listen, Jenn, biologists everywhere are trying to decode the language of DNA. Look up at the redwoods—those are the genes! They’re like Christmas lights strung along a DNA strand. Isn’t it beautiful?"

As they drive along California’s US 101 toward Mendocino, heading to his unfinished cabin in the woods, Kary gazes up at the ethereal lights among the branches, imagining that perhaps the psychedelic substances in his system might connect him to the trees, allowing them to share this vibrant vision.

"Can I sing you a song, Jenn?" Kary begins without waiting for a response, his tone enthusiastic but off-key:

i is for adenine. T is for thymine. C is for cytosine. G is for guanine.

These are the letters in our DNA code! Any three letters spell an amino acid, And a chain of amino acids forms a protein, And together, they create us human beings!

Wooo! Wooo wooooo!

DNA is a long chain of letters, An alphabet made of only As, Ts, Gs, and Cs! Mistake that code, and you get a disease!

DNA’s two strands twist into a helix, The code in one strand has a counterpart, Because A pairs with T And G pairs with C.

Wooo! Wooo wooooo!

Kary’s song fades after his last enthusiastic "wooo," leaving him breathless as he coughs lightly to conclude the performance.

Jennifer rests her head back, closing her eyes, preparing for an evening filled with Kary's colorful musings. Suddenly, he straightens up, his earlier ramblings now entwined with clarity, like a lucid dream.

"Jenn, we need to explore new applications for our oligos. We understand that these short DNAs can bind to specific genetic sequences due to the complementary nature of A-T and G-C pairing. We can engineer oligos to target specific genes and then amplify them!"

Jennifer sits up, realizing the implications of Kary's work on her own position as a chemist. They first met in the lab when she had to salvage an experiment he had botched. Kary’s brilliant creativity was often hindered by his less-than-stellar manual skills, and Jennifer's practical ingenuity had captivated his heart.

"I understand the concept of specific binding, Kary, but I’m confused about how your amplification idea comes into play. You want to create multiple copies of a specific gene, right? But how does the short DNA binding facilitate the amplification of the longer DNA?"

To her dismay, Kary bursts into song once more:

At the core of all cells, from bacteria to man, Are coils and coils of DNA, Dictating our Fates like the Moirai, Who spin, measure, and sever our life-thread, And mark the date on our tombstones with dread.

For a cell to divide, the DNA must duplicate, So both daughter cells receive their own copy. The task is assigned to a protein machine Called DNA polymerase, Copying our genes until the end of their days.

Woooo woooo…!

Where the polymerase encounters an A, it inserts a T, Where it sees a C, it places a G, And vice versa, for a strand of DNA, As long as the letters are read, The new strand has the complementary letter instead.

For polymerase to create a DNA copy, It requires a short strand of DNA to initiate. Where the short DNA concludes, the polymerase adds The complement to whatever The long strand possesses as the next letter.

Woooo woooooooooo cough cough!

Jennifer sits up, beginning to grasp Kary's concept. The short DNA oligonucleotides they produce at Cetus could serve as primers for the polymerase. She seeks confirmation from Kary:

"So, let me clarify… The primer binds to a specific gene region due to complementary DNA pairing—this part we already understand. Then the polymerase reads the longer DNA strand to which the primer is attached and extends it to create a second strand of DNA. Am I correct?"

Kary beams at her, a grin spreading across his face.

"But Kary, you’re still left with just one copy. You haven’t really amplified the DNA significantly."

Kary, finding his unique method of conveying scientific ideas through song, continues:

DNA’s two strands are connected Only by fragile hydrogen bonds. Heat them up and the two helical strands Will separate like a snowman in spring.

An electric thrill races through Jennifer’s mind, igniting a flash of recognition.

"So, you repeat the DNA melting and polymerase copying reactions repeatedly?" she inquires.

In response, Kary bellows joyfully:

With each repetition, you only double, But each double compounds, One becomes two, two becomes four, then eight. After thirty-one doublings, you’ll have 8,388,608!

Woooo woooooooooo!! cough cough!

This rapid doubling is the chain reaction that drives the amplification of DNA, hence the term polymerase chain reaction, or PCR.

"But wait, there’s a critical piece missing," Jennifer interjects, contemplating the gaps in their vibrant conversation. "You want to amplify a specific DNA segment, so how…?"

She hesitates, and Kary glances at her with an eager grin, ready to pounce on her realization.

"Oh my goodness! You’ll need a second primer! A primer for each end of the DNA segment you wish to amplify! The polymerase will extend the DNA in one direction from one primer and then, after melting the DNA strands, it will extend the other strand in the opposite direction from the other primer! The polymerase extensions move toward each other, so only the DNA between both primers gets amplified!"

Oh yeeaaaaahhhhh oh oh oh yeeeahhhhhhh!!!!!

The energy in the car surges as their minds synchronize. Their grins overlap, like photographs layered on transparent sheets, as laughter and excitement fill the space between them.

Jennifer, the chemist with remarkable skills, begins to consider the components necessary for this reaction:

A DNA polymerase will join As, Ts, Gs, and Cs into a long strand forming the new DNA. Thus, these letters, the raw materials for the polymerase, must be plentiful.

The specific form of these nucleotides features three attached phosphate groups—like a short but powerful tail. Each phosphate acts as a battery, fueling the reaction and ensuring the letters bind to the growing DNA chain.

The polymerase is essential to the reaction, along with the DNA to be copied and the short DNA oligos that Cetus (and Jennifer) will synthesize. The polymerase requires specific pH levels and salt concentrations to mimic its natural cellular environment. All these factors must be included.

And, naturally, this process will occur in an aqueous solution—mostly water, with tiny amounts of the various components she just listed. "We are essentially bags of seawater," she thinks. This is the optimal environment for the polymerase to thrive, coaxing it to produce millions of DNA copies, but only of the segment located between the two primers.

Jennifer drifts back to sleep, her mind swirling with visions of molecules dancing in intricate patterns.

Her dreams fluctuate between extremes, fueling the reactions. She envisions oceans boiling and the lengthy DNA double helix unraveling like strands of overcooked spaghetti. Then, Poseidon commands the waters to cool to warm temperatures, allowing the short DNA primers to attach to the long DNA strands. Like whales approaching fishing lines, the polymerase aligns with the DNA where the primer binds. The polymerase consumes the phosphate-powered letters of the genetic code—As, Ts, Gs, and Cs—swimming into the polymerase’s mouth and emerging as part of a new, intertwined DNA strand.

The cycle repeats, with oceans boiling again, until the waters overflow with coiled ropes of freshly synthesized DNA.

Postscript to a life…

Jennifer and Kary shared two tumultuous years during which Kary worked to validate his PCR process while also navigating the complexities of their relationship. He likely wasn’t the easiest person to be with, and she probably made the right choice to move on. He felt heartbroken but ultimately succeeded in making PCR a reality.

Others significantly improved PCR, particularly by discovering heat-resistant polymerases capable of withstanding the high temperatures that would denature normal proteins, including typical DNA polymerases.

The key was a bacterium thriving in the hot springs of Yellowstone National Park. Biologists Thomas Brock and Hudson Freeze named this thermophilic bacterium Thermus aquaticus, or Taq for short.

Taq polymerase has gained acclaim in laboratories worldwide for its vital role in simplifying and accelerating the PCR process. In Kary’s original method, each cycle following the boiling of the DNA solution required the addition of more polymerase—often more than thirty cycles were necessary.

Kary received the 1993 Nobel Prize in Chemistry, which fueled his drug use and surfing lifestyle, along with international speaking engagements, often accompanied by his fourth wife, Nancy Cosgrove.

The Moirai, the three Greek goddesses known as the Fates, shaped Kary’s life, as they do for all mortals. Clotho spun the thread, Lachesis measured its length, and Atropos wielded the dreaded shears, cutting the thread of Kary’s life on August 7, 2019.

Postscript…

Since the 1980s, PCR has found applications in an astonishing array of fields, including criminal investigations, gene cloning, DNA sequencing (such as the Human Genome Project), disease detection (including COVID-19), and much more.

Thank you…

I extend my gratitude to Christine Sander for inspiring me to write about PCR in a more accessible manner. I recognize that there are far more effective ways to convey this information and that I may have fallen short, but I relished the challenge. I hope you enjoy this, Christine, as well as others who have patiently endured my various attempts to communicate scientific concepts.