Polynucleotide code

Section 28 11 Three RNAs are involved m gene expression In the transcription phase a strand of messenger RNA (mRNA) is synthesized from a DNA tern plate The four bases A G C and U taken three at a time generate 64 possible combinations called codons These 64 codons comprise the genetic code and code for the 20 ammo acids found m proteins plus start and stop signals The mRNA sequence is translated into a prescribed protein sequence at the ribosomes There small polynucleotides called... 

The sequence of bases in the polynucleotide chain is also important because it determines the exact sequence of amino acids used in the synthesis of a protein. Twenty amino acids are commonly found in proteins, while only four bases are used in the DNA molecule. Thus, more than one base must specify each amino acid. The genetic code is in fact read as triplets and there are 64 possible triplet combinations using 4 nucleotides. Each triplet of nucleotides is termed a codon, and given the redundancy, some amino acids are specified by more than one codon. 

Nucleic Acid. A nucleic acid is a natural polynucleotide. It is a sugar-phosphate chain with purine and pyrimidine bases attached to it, as shown in Chart 10. If the sugar is deoxyribose and the pyrimidine bases are cytosine and thymine, the nucleic acid is deoxyribonucleic acid, DNA if the sugar is ribose, and the pyrimidine bases are (mostly) cytosine and uracil, the nucleic acid is ribonucleic acid, RNA. The sequence of bases may appear arbitrary and random, but it constitutes a meaningful code (see Code Word). In double-stranded nucleic acids,... 

Polynucleotide phosphoiylase can be used in the laboratory to prepare RNA polymers with many different base sequences and frequencies. Synthetic RNA polymers of this sort were critical for deducing the genetic code for the amino acids (Chapter 27). 

Another important technique was based on the observation that synthetic trinucleotides induced the binding to ribosomes of tRNA molecules that were "charged" with their specific amino acids 38/39 For example, the trinucleotides UpUpU and ApApA stimulated the binding to ribosomes of 14C-labeled phenylalanyl-tRNA and lysyl-tRNA, respectively. The corresponding dinucleotides had no effect, an observation that not only verified the two codons but also provided direct evidence for the triplet nature of the genetic code. Another powerful approach was the use of artificial RNA polymers, synthesized by combined chemical and enzymatic approaches.40 For example, the polynucleotide CUCUCUCUCU led to the synthesis by ribosomes of a regular alternating polypeptide of leucine and serine. 

The codons of the mRNA on the ribosomes are read from the 5 to the 3 end. Thus the synthetic polynucleotide (5 )A-A-A-(A-A-A) -A-A-C(3 ) contains the code for lysine (A-A-A) and asparagine (A-A-C) the actual polypeptide obtained using this mRNA in a cell-free system was Lys-(Lys),-Asn, and not Asn-(Lys) -Lys. 

Polynucleotide phosphorylase was used to produce RNA of random sequence, the composition of which reflected the mixture of nucleoside diphosphates in the reaction mixture. Mixed polynucleotides containing two bases were used in the incorporating system and shown to incorporate a pattern of amino acids consistent with a triplet code, but the observed incorporation could not define the code sequence. 

Nucleoproteinoids composed from polynucleotide and basic proteinoid have activity to synthesize peptides selectively 28,59). The mechanism is unknown. This is a way to resolve the genetic coding mechanism. Affinity, for example, hydrophobicity or hydrophilicity, between amino acid and nucleic acid is related to their anticodonic... 

The pEU3b plasmid was digested with Spe I and blunted with T4 polynucleotide kinase. The plasmid was then digested with Sal I. The coding region for yeast ubiquitin was prepared as follows. 

Fig. 10 Model protocell systems, a An encapsulated polymerase (polynucleotide phos-phorylase) can synthesize RNA from nucleoside diphosphates such as ADP [79,80], b RNA can be synthesized by a template-dependent T7 RNA polymerase [83], c Proteins such as green fluorescent protein (GFP) can be synthesized by an encapsulated translation system [84], If mRNA coding for hemolysin is also present, the hemolysin forms a pore in the lipid bilayer. Amino acids then permeate the bilayer, and protein synthesis can continue for several days [85]...

Tinoco, I. Hypochromism in polynucleotides. J. Am. Chem. Soc. 82, 4785 (1960). Valdemoro, C., and S. Fraga The eletronic structure of puric and pyrimidinic bases and the biological codes. Technical Report TC-6701, Department of Chemistry, University of Alberta (1967a). 

Khorana, H. G. Polynucleotide synthesis and the genetic code. Federation Proc. 24, 1473 (1965). 

C. Basilio, and S. Ochoa Synthetic polynucleotides and the amino acid code. 

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 genetic information of living organisms is coded in DNA in the form of base pair sequences. There are four types of nucleotides, which are linked to a polynucleotide with a sugar-phosphate backbone. The arrangement of nucleotides along the one-dimensional chain is called the primary structure of DNA, which directly encodes the primary structure of proteins by means of... 

The fidelity of cellular repair and reproduction is determined by a coding system based on polynucleotides - deoxyribonucleic acid (DNA) and ribonucleic acid (RNA). In general (with some inevitable exceptions of course), the information flow is from DNA molecules (genes) which are transcribed to yield RNA molecules which in turn are translated on complex macromolecular protein-RNA assemblies called ribosomes to yield proteins (polymers of amino acids linked by peptide bonds). 

Nucleic adds are well-known to play an important role in both the replicative and the transcriptive functions of the genetic codes. DNA, one of the nucleic adds, for example, has a double stranded structure consisting of two polynucleotide chains twisted about each other in a double helix, which is stabilized by spedal base-base interactions of nudeic adds. The interactions among such purine and pyrimidine families are apparently a common subject of substantial interest among chemists in the fields of organic, macromolecular, and biochemical syntheses. 

Specific inhibition of templated biosynthesis by electroneutral polynucleotide analogs can be achieved even with complex templates Messenger RNA coding for globin, similarly to other messenger RNA molecules, contains a polyadenylate sequence located... 

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