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Francis Crick QUOTES / QUOTATIONS
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
By testing such mutants in pairs we can assign them all without exception to one of two classes which we call + and - .
Quotation of Francis Crick
By using polymers of different composition and assuming a triplet code one can deduce limited information about the composition of certain triplets.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
If poly A is added to poly U, to form a double or triple helix, the combination is inactive.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
In a cell in which DNA is the genetic material it is not believed that DNA itself controls protein synthesis directly.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
It seems virtually certain that a single chain of RNA can act as messenger RNA, since poly U is a single chain without secondary structure.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
That is, that one end of the gene codes for the amino end of the polypeptide chain and the other for the carboxyl end, and that as one proceeds along the gene one comes in turn to the codons in between in the linear order in which the amino acids are found in the polypeptide chain.
Quotation of Francis Crick
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.
Quotation of Francis Crick
The crucial experiment is to put together, by genetic recombination, three mutants of the same type into one gene.
Quotation of Francis Crick
The genetic code describes the way in which a sequence of twenty or more things is determined by a sequence of four things of a different type.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
Twenty different kinds of amino acid are commonly found in protein, and four main kinds of base occur in nucleic acid.
Quotation of Francis Crick
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.
Quotation of Francis Crick
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.
Quotation of Francis Crick
We've discovered the secret of life.
Quotation of Francis Crick
What is clear is that most of the experimental evidence so far presented falls short of proof in almost all cases.
Quotation of Francis Crick