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In spite of the extensive variation of form and function among organisms, several fundamental criteria characterize all life. Some of the macroscopic properties that characterize all of life are 1 replication, 2 heritability characteristics of descendents are correlated with those of ancestors3 catalysis, and 4 energy utilization metabolism.
At a very minimum, these four functions are required to generate a physical historical process that can be described by a phylogenetic tree. If every living species descended from an original species that had these four obligate functions, then all living species today should necessarily have these functions a somewhat trivial conclusion.
Most importantly, however, all modern species should have inherited the structures that perform these functions. Thus, a basic prediction of the genealogical relatedness of all life, combined with the constraint of gradualism, is that organisms should be very similar in the particular mechanisms and structures that execute these four basic life processes.
The common polymers of life The structures that all known organisms use to perform these four basic processes are all quite similar, in spite of the odds. All known living things use polymers to perform these four basic functions.
Organic chemists have synthesized hundreds of different polymers, yet the only ones used by life, irrespective of species, are polynucleotides, polypeptides, and polysaccharides. Regardless of the species, the DNA, RNA and proteins used in known living systems all have the same chirality, even though there are at least two chemically equivalent choices of chirality for each of these molecules.
For example, RNA has four chiral centers in its ribose ring, which means that it has 16 possible stereoisomers—but only one of these stereoisomers is found in the RNA of known living organisms. Nucleic acids are the genetic material of life Ten years after the publication of The Origin of Species, nucleic acids were first isolated by Friedrich Miescher in It took another 75 years after this discovery before DNA was identified as the genetic material of life Avery et al.
It is quite conceivable that we could have found a different genetic material for each species. In fact, it is still possible that newly identified species might have unknown genetic materials. All known organisms base replication on the duplication of this molecule.
The DNA used by living organisms is synthesized using only four nucleosides deoxyadenosine, deoxythymidine, deoxycytidine, and deoxyguanosine out of the dozens known at least occur naturally and many more have been artificially synthesized Rozenski et al.
Protein catalysis In order to perform the functions necessary for life, organisms must catalyze chemical reactions.
In all known organisms, enzymatic catalysis is based on the abilities provided by protein molecules and in relatively rare, yet important, cases by RNA molecules. There are over naturally occurring amino acids known Voet and Voetp.
The univeral genetic code There must be a mechanism for transmitting information from the genetic material to the catalytic material. All known organisms, with extremely rare exceptions, use the same genetic code for this. The few known exceptions are, nevertheless, simple and minor variations from the "universal" genetic code see Figure 1.
The scientists who cracked the genetic code in the 's and 's worked under the assumption that the code was universal or nearly so Judsonp. These scientists which included Francis Crick, Sydney Brenner, George Gamow, and several others all made this assumption and justified it based upon evolutionary reasoning, even in the complete absence of any direct experimental evidence for a universal code.
The standard genetic code and known variant nuclear codes. There was no evidence whatever for this; Yet universality seemed inevitable for an obvious reason: For instance, innearly ten years before the genetic code was finally solved, Sydney Brenner published an influential paper in which he concluded that all overlapping triplet codes were impossible if the code was universal Brenner This paper was widely considered a landmark work, since many researchers were leaning towards an overlapping code.
Of course, it turned out that Brenner was correct about the nature of the true code. Infive years before the code was deciphered, Crick referenced Brenner's work in his landmark report in the journal Nature, "General nature of the genetic code for proteins" Crick et al.This Is The Plain Truth About How To Talk To Women This is the straight truth about how to talk to women.
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