Francis Crick
We've discovered the secret of life.
It seems likely that most if not all the genetic information in any organism is carried by nucleic acid - usually by DNA, although certain small viruses use RNA as their genetic material.
Moreover the incorporation requires the same components needed for protein synthesis, and is inhibited by the same inhibitors. Thus the system is most unlikely to be a complete artefact and is very probably closely related to genuine protein synthesis.
It is one of the more striking generalizations of biochemistry - which surprisingly is hardly ever mentioned in the biochemical textbooks - that the twenty amino acids and the four bases, are, with minor reservations, the same throughout Nature.
We are sometimes asked what the result would be if we put four +'s in one gene. To answer this my colleagues have recently put together not merely four but six +'s.
Unfortunately it makes the unambiguous determination of triplets by these methods much more difficult than would be the case if there were only one triplet for each amino acid.
This seems highly likely, especially as it has been shown that in several systems mutations affecting the same amino acid are extremely near together on the genetic map.
It would appear that the number of nonsense triplets is rather low, since we only occasionally come across them. However this conclusion is less secure than our other deductions about the general nature of the genetic code.
It now seems very likely that many of the 64 triplets, possibly most of them, may code one amino acid or another, and that in general several distinct triplets may code one amino acid.
It now seems certain that the amino acid sequence of any protein is determined by the sequence of bases in some region of a particular nucleic acid molecule.
It has yet to be shown by direct biochemical methods, as opposed to the indirect genetic evidence mentioned earlier, that the code is indeed a triplet code.
If, for example, all the codons are triplets, then in addition to the correct reading of the message, there are two incorrect readings which we shall obtain if we do not start the grouping into sets of three at the right place.
If the code does indeed have some logical foundation then it is legitimate to consider all the evidence, both good and bad, in any attempt to deduce it.
If poly A is added to poly U, to form a double or triple helix, the combination is inactive.
The meaning of this observation is unclear, but it raises the unfortunate possibility of ambiguous triplets; that is, triplets which may code more than one amino acid. However one would certainly expect such triplets to be in a minority.
The balance of evidence both from the cell-free system and from the study of mutation, suggests that this does not occur at random, and that triplets coding the same amino acid may well be rather similar.
How is the base sequence, divided into codons? There is nothing in the backbone of the nucleic acid, which is perfectly regular, to show us how to group the bases into codons.
For simplicity one can think of the + class as having one extra base at some point or other in the genetic message and the - class as having one too few.
Do codons overlap? In other words, as we read along the genetic message do we find a base which is a member of two or more codons? It now seems fairly certain that codons do not overlap.
Attempts have been made from a study of the changes produced by mutation to obtain the relative order of the bases within various triplets, but my own view is that these are premature until there is more extensive and more reliable data on the composition of the triplets.
A final proof of our ideas can only be obtained by detailed studies on the alterations produced in the amino acid sequence of a protein by mutations of the type discussed here.
A comparison between the triplets tentatively deduced by these methods with the changes in amino acid sequence produced by mutation shows a fair measure of agreement.
Avoid the temptation to work so hard that there is no time left for serious thinking.Collection: Thinking
There is no scientific study more vital to man than the study of his own brain. Our entire view of the universe depends on it.Collection: Science
Biologists must constantly keep in mind that what they see was not designed, but rather evolved.Collection: Science
The dangerous man is the one who has only one idea, because then he'll fight and die for it.Collection: Fighting
You’re nothing but a pack of neurons.Collection: Neurons
A theory should not attempt to explain all the facts, because some of the facts are wrongCollection: Facts
A good scientist values criticism almost higher than friendship: no, in science criticism is the height and measure of friendship.Collection: Criticism
Almost all aspects of life are engineered at the molecular level, and without understanding molecules we can only have a very sketchy understanding of life itself.Collection: Life
Evolution is cleverer than you are.Collection: Science
Consciousness is somehow a by-product of the simultaneous, high frequency firing of neurons in different parts of the brain. It's the meshing of these frequencies that generates consciousness, just as tones from individual instruments produce the rich, complex, & seamless sounds of a symphony orchestraCollection: Inspiration
The ultimate aim of the modern movement in biology is in fact to explain all biology in terms of physics and chemistry.Collection: Facts
My own prejudices are exactly the opposite of the functionalists': "If you want to understand function, study structure".Collection: Want
It is essential to understand our brains in some detail if we are to assess correctly our place in this vast and complicated universe we see all around us.Collection: Brain
An honest man, armed with all the knowledge available to us now, could only state that in some sense, the origin of life appears at the moment to be almost a miracle, so many are the conditions which would have had to have been satisfied to get it going.Collection: Men
Christianity may be OK between consenting adults in private but should not be taught to young children.Collection: Children
Chance is the only source of true novelty.Collection: Life
A busy life is a wasted life.Collection: Life
Since I essentially knew nothing, I had an almost completely free choice.Collection: Choices
Free will is located in or near the anterior cingulate sulcus.Collection: Free Will
One of the most frightening things in the Western world, and in this country in particular, is the number of people who believe in things that are scientifically false. If someone tells me that the earth is less than 10,000 years old, in my opinion he should see a psychiatrist.Collection: Country
It is not easy to convey, unless one has experienced it, the dramatic feeling of sudden enlightenment that floods the mind when the right idea finally clinches into place.Collection: Ideas
What could be more foolish than to base one's entire view of life on ideas that, however plausible at the time, now appear to be quite erroneous? And what would be more important than to find our true place in the universe by removing one by one these unfortunate vestiges of earlier beliefs?Collection: Views
It is not easy to convey, unless one has experienced it, the dramatic feeling of sudden enlightenment that floods the mind when the right idea finally clicks into place. One immediately sees how many previously puzzling facts are neatly explained by the new hypothesis. One could kick oneself for not having the idea earlier, it now seems so obvious. Yet before, everything was in a fog.Collection: Fog
In the fullness of time, educated people will believe there is no soul independent of the body, and hence no life after death.Collection: Believe
When you start in science, you are brainwashed into believing how careful you must be, and how difficult it is to discover things. There's something that might be called the 'graduate student syndrome'; graduate students hardly believe they can make a discovery.Collection: Believe
There is no form of prose more difficult to understand and more tedious to read than the average scientific paper.Collection: Science
A man who is right every time is not likely to do very much.Collection: Men
If revealed religions have revealed anything it is that they are usually wrong.Collection: Atheist