Genetic code information

The significance of Sanger s work is immense. It proved for the first time that the structure of a protein is unique that is, aU molecules of bovine insulin, for example, possess the same sequence of amino acids along the polypeptide chains. This sequence has no obvious order, but it is unique. This singular finding requires that there is a genetic code information encoded in a molecule which specifies the sequence of amino acids in the insulin molecule and, for that matter, in all protein molecules. 

Synthetic polynucleotides and the genetic code. Informational Macromolecules, edited by H. J. Vogel, V. Bryson, and J. O. Lampen. New York Academic Press 1963. 

The two strands which make up DNA are held together by hydrogen bonds between complementary pairs of bases adenine paired with thymine and guanine paired with cytosine. The integrity of the genetic code (and of life as we know it) depends on error-free transmission of base-pairing information. 

The cell must possess the machinery necessary to translate information accurately and efficiently from the nucleotide sequence of an mRNA into the sequence of amino acids of the corresponding specific protein. Clarification of our understanding of this process, which is termed translation, awaited deciphering of the genetic code. It was realized early that mRNA molecules themselves have no affinity for amino acids and, therefore, that the translation of the information in the mRNA nucleotide sequence into the amino acid sequence of a protein requires an intermediate adapter molecule. This adapter molecule must recognize a specific nucleotide sequence on the one hand as well as a specific amino acid on the other. With such an adapter molecule, the cell can direct a specific amino acid into the proper sequential position of a protein during its synthesis as dictated by the nucleotide sequence of the specific mRNA. In fact, the functional groups of the amino acids do not themselves actually come into contact with the mRNA template. 

Every gene contains DNA with a unique sequence of bases forming a genetic code containing the information an organism uses to iive and repiicate itseif Many years of research have resuited in an understanding of how the information content of DNA is transiated into particuiar biochemicai substances and how DNA repiicates. The processes inciude unwinding of the DNA doubie heiix so its code can be read or dupiicated. 

The vector of properties is a kind of chromosome, a code that defines the genotype of the individual. This sequence of values specifies the "genetic makeup" that (possibly uniquely) defines the animal. In Daisy s case, not all of the animal s characteristics are defined by her biological genetic code we have included in the vector other characteristics that would help to pick her out from the kine (cattle) crowd. In a similar way, a single GA solution can be constructed as a "chromosome" or genome in vector form, which contains all the information needed to define the potential solution to a scientific problem. 

Fig. 1.5 Schematic representation of the evolution of life from its precursors, on the basis of the definition of life given by the authors. If bioenergetic mechanisms have developed via autonomous systems, the thermodynamic basis for the beginning of the archiving of information, and thus for a one-polymer world such as the RNA world , has been set up. Several models for this transition have been discussed. This phase of development is possibly the starting point for the process of Darwinian evolution (with reproduction, variation and heredity), but still without any separation between genotype and phenotype. According to the authors definition, life begins in exactly that moment when the genetic code comes into play, i.e., in the transition from a one-polymer world to a two-polymer world . The last phase, open-ended evolution, then follows. After Ruiz-Mirazo et al. (2004)...

The close connection of this enzyme family with the transfer of genetic information has made it a popular object of study when dealing with questions regarding the formation and evolution of the genetic code (see Sect. 8.1). It is now agreed that the aminoacyl-tRNA synthetases are a very ancient enzyme species which do not, however, arise from one single primeval enzyme, but from at least two, corresponding to the synthetase classes. 

The information contained in the DNA (i.e., the order of the nucleotides) is first transcribed into RNA. The messenger RNA thus formed interacts with the amino-acid-charged tRNA molecules at specific cell organelles, the ribosomes. The loading of the tRNA with the necessary amino acids is carried out with the help of aminoacyl-tRNA synthetases (see Sect. 5.3.2). Each separate amino acid has its own tRNA species, i.e., there must be at least 20 different tRNA molecules in the cells. The tRNAs contain a nucleotide triplet (the anticodon), which interacts with the codon of the mRNA in a Watson-Crick manner. It is clear from the genetic code that the different amino acids have different numbers of codons thus, serine, leucine and arginine each have 6 codewords, while methionine and tryptophan are defined by only one single nucleotide triplet. 

Some of the many hypotheses and models will be presented briefly. The physicochemical hypothesis refers to a minimalisation of the liability of the genetic code to cause errors in information transmission. The error rate can fall when amino acids with similar codons have similar properties, such as the presence of hydrophilic... 

Table 8.2 According to the co-evolution theory proposed by Wong, the biosynthetic routes to amino acids from their precursors could perhaps provide information on the evolution of the genetic code (Wong, 1975)...

A further (mathematical) model for the evolution of the genetic code was devised by Carl Woese and co-workers. This dynamic theory provides information on the evolvability and universality of the genetic code. One conceptual difficulty was due to the fact that it had been overlooked that the genetic code was highly communal... 

RNA RNA (ribonucleic acid) is an information encoded strand of nucleotides, similar to DNA, but with a slightly different chemical structure. In RNA, the letter U (uracil) is substituted for T in the genetic code. RNA delivers DNA s genetic message to the cytoplasm of a cell where proteins are made. 

There are many potential molecules and possible routes to the synthesis of biomolecules that might form the basis of a primitive metabolism but thus far we have not addressed the question of information propagation or Darwinian evolution. Information storage must be contained within a sequence, such as words in a sentence or the base sequences within the genetic code, and that requires a polymerisation reaction, which is preferably autocatalytic to reproduce the information accurately. Peptides and nucleotides have this property, although the condensation reaction joining them together needs to be activated. 

RNA World hypothesis The recognition that RNA can self-replicate leads to the idea that information propagation and the genetic code first started with RNA. 

Nucleic acid Either of two types of macromolecule (DNA or RNA) formed by polymerization of nucleotides. Nudeic adds are found in all living cells and contain the information (genetic code) for the transfer of genetic information from one generation to the next. [NIH]... 

The primary goal of peptide mapping is the verification of the amino acid sequence deduced from the genetic code of the recombinant protein. The protein backbone gets cleaved by typically two or three different endoproteinases like Lys-C, trypsin, and Glu-C to achieve maps with sequence-overlapping peptide fragments. These peptide mixtures can then be separated by LC or CE and analyzed on-line by MS to obtain sequence information. Often simple mass analysis matches the predicted primary sequence of the protein. However, sometimes mutations can lead to isobaric masses of peptides that can be overseen, if no further sequence analysis like N-terminal Edman sequencing and MS/MS is carried out. 

To transcribe information from DNA to mRNA, one strand of the DNA is used as a template. This is called the anticoding, or template, strand and the sequence of mRNA is complementary to that of the template DNA strand (Fig. A2.8) (i.e., C->G, G->C, T->A, and A U note that T is replaced by U in mRNA). The other DNA strand, which has the same base sequence as the mRNA, is called the coding, or sense, strand. There are 64 (4 x 4 x 4) possible triplet codes of the four bases 61 are used for coding amino acids and three for termination signals. As there are 20 amino acids for the 61 codes, some triplets code for the same amino acid. A table of the genetic code is presented in Exhibit A2.2. 

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