Francis Crick: Centenary

Today marks the 100th birthday of one of my heroes, Francis Crick. Along with the now pariah James Watson, Crick realised the structure of the DNA double helix in 1953, a discovery for which they shared a Nobel Prize in 1962. This structure is so fundamental to the function of biology’s most famous molecule that it has pretty much become the symbol of biology.

The pair were aided enormously by the X-Ray crystallography work of Rosalind Franklin who sadly died in 1958. Her Photograph 51 (see image above) was the keystone to the discovery. Being dead excludes you from eligibility for a Nobel Prize and so we will never know if she would have been snubbed, like so many women were at that time, or if she would have been given the credit she rightly deserved.

In any case, Crick and Watson are the names that everyone remembers, some say rightly. Whilst all the evidence was there for people to see, some argue that only they had the gumption to put it all together and to understand the implications of the double helix.

It would seem that Crick was a nice enough chap, whilst Watson is now regarded as a bigoted racist who has been largely ostracised from the scientific community. He famously sold his Nobel Prize in 2014 pleading poverty. It was bought by a wealthy Russian for more than $4 million who then promptly returned it straight to Watson, so don’t feel too sorry for him.

From the window of the lab I work in I have been able to watch the rise of the Francis Crick Institute as it has been built over the past few years. It is due to open this summer and is destined to be a flagship biomedical research centre. Led by Sir Paul Nurse, another Nobel laureate, The Crick strategy is to bring together multidisciplinary teams in one building to tackle problems from multiple angles. Expect to see a lot of exciting science coming out of there once they’re up and running.

Returning to the man himself, I’m reminded of a letter he wrote to his 12 year old son just a few weeks after the discovery. The letter was sold at auction in 2013 for $5.3 million, making it the most expensive letter in history.

19 Portugal Place
Cambridge

19 March ‘53

My Dear Michael,

Jim Watson and I have probably made a most important discovery. We have built a model for the structure of dex-oxi-ribose-nucleic-acid (read it carefully) called D.N.A. for short. You may remember that the genes of the chromosomes — which carry the hereditary factors — are made up of protein and D.N.A.
Our structure is very beautiful. D.N.A. can be thought of roughly as a very long chain with flat bits sticking out. The flat bits are called the “bases”. The formula is rather like this.

    |
sugar —— base
|
phosphorus
|
sugar —— base
|
phosphorus
|
sugar —— base
|
phosphorus

and so on.

Now we have two of these chains winding round each other — each one is a helix — and the chain, made up sugar and phosphorus, is on the outside, and the bases are all on the inside. I can’t draw it very well, but it looks like this.

[diagram of double helix]

The model looks much nicer than this.
Now the exciting thing is that while there are 4 different bases, we find we can only put certain pairs of them together. The bases have names. They are Adenine, Guanine, Thymine & Cytosine. I will call them A, G, T and C. Now we find that the pairs we can make — which have one base from one chain joined to one base from another — are only

A with T

and

G with C.

Now on one chain, as far as we can see, one can have the bases in any order, but if their order is fixed, then the order on the other chain is also fixed. For example, suppose the
first chain goes ↓ then the second must go

A – – – – – – – – – – – – – – – – – T
T – – – – – – – – – – – – – – – – – A
C – – – – – – – – – – – – – – – – -G
A – – – – – – – – – – – – – – – – – T
G – – – – – – – – – – – – – – – – -C
T – – – – – – – – – – – – – – – – – A
T – – – – – – – – – – – – – – – – – A

It is like a code. If you are given one set of letters you can write down the orders.
Now we believe that the DNA is a code. That is, the order of the bases (the letters) makes one gene different from another gene (just as one page of print is different from another). You can now see how Nature makes copies of the genes. Because if the two chains unwind into two separate chains, and if each chain then makes another chain come together on it, then because A always goes with T, and G with C, we shall get two copies where we had one before.
For example

A — T
T — A
C — G
A — T
G — C
T — A
T — A

chains
↙ separate ↘

A                         T
T                         A
C                         G
A                         T
G                         C
T                          A
T                          A


new chains form

A — T                            T — A
T — A                           A — T
C — G                           G — C
A — T                            T — A
G — C                           C — G
T — A                           A — T
T — A                           A — T

In others words we think we have found the basic copying mechanism by which life comes from life. The beauty of our model is that the shape of it is such that only these pairs can go together, though they could pair up in other ways if they were floating about freely. You can understand that we are very excited. We have to have a letter off to Nature in a day or so.
Read this carefully so that you understand it. When you come home we will show you the model.

Lots of love,
Daddy

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