"We have discovered the secret of life!"

Leonor Fini, Lithography.

"Watson, on the 28th of February, about 10 o'clock in the morning, comes into the lab and starts taking the models of the nucleotides that have been cut for them by the machine shop and starts putting them together in different ways and gives up on the like-by-like, and instead begins combining different with different, and sees that at equal spacing, you can make the Ts fit with As and get two hydrogen bonds.
And you can make the Cs fit with Gs, and get three hydrogen bonds.
And they would fit perfectly into a double helix if the two strands were running in the opposite direction, and would nicely reproduce the spacing evident in photograph 51 and the dyad symmetry present in that.
And Crick comes into the lab about an hour later.
Watson shows it to Crick, and Crick instantly realizes, this feels like an answer.
Not this other thing you were doing a few days ago, Jim.
This feels good.
Watson is still cautious-- because they've already blown it before in producing the wrong structures-- and really wants before they tell anybody to have the machine shop build a careful model of DNA to show that the whole thing will really work.
And as partnerships go, they go to lunch at the Eagle Pub.
And although Watson says, let's not tell anybody yet, Crick sits down at the Eagle Pub and announces to anyone who will hear, 'we have discovered the secret of life!'.

And as it turns out, they had.

Because it turns out that when the model was carefully built, the model checks out."  7.00x Intro to Biology- The Secret of Life  Eric Lander PhD. "DNA Structure: the Race".

Crick and Watson's DNA molecular model, 1953.

http://www.anselm.edu/homepage/jpitocch/genbio/doublehelix.JPG

Crick and Watson write a paper for "Nature". It is one page long. And it's probably the most famous paper in the 20th century. It starts, "we wish to suggest a structure for the salt of deoxyribonucleic acid, DNA. This structure has novel features which are of considerable biological interest." Second paragraph, "a structure for nucleic acid has recently been proposed by Pauling and Corey (...). "But without the acidic hydrogen atoms, it is not clear what forces would hold the structure together, especially as the negatively charged phosphates near the axis will repel each other." "So second paragraph is dismissing Pauling's model. And then it goes on and it explains the dyad symmetry and all this and gets down to the bottom of the page and, well, why is this model so good?

Why is this model so good?

It isn't just that it explains the X-ray crystallographic data. It isn't just that it explains Chargaff's Rules (A-T and C-G having same ratios). A model that has A matching T, G matching C, Cs matching Gs, Ts matching As-- a model that does that has one amazing property. It explains something.

It explains heredity.

It explains heredity because each of those strands alone is a complete template for the other strand. If I give you one strand, AGCTAAGG, you can fill in the other strand. If I separate these two strands, each can be used as a template to make a copy of that information. That is a stunning observation. Suddenly, the whole notion of how you can replicate information is clear. You replicate information by having a double helix where the information is fully specified on either of the two strands. You peel them apart, and you can put together two double helices. This is how chromosomes will replicate. This is what mitosis and meiosis must be about-- the transmission of genetic information. That's why Chargaff's Rules matter.

That's why Crick goes into the Eagle Pub and he says, 'we've discovered the secret of life!'."

7.00x Intro to Biology- The Secret of Life  Eric Lander PhD. "DNA Structure: the Race".