DNA genetic code

RNA has a polymeric structure similar to that of DNA with the substitution of a uracil for thymine. The overall structure of RNA can be single or double-stranded and RNA performs a variety of functions having to do with the transcription and translation of the DNA genetic code into functional proteins. 

All proteins are initially synthesized in the body from only 20 different amino acids, called the common amino acids. Each of these has a spedlic codon or set of codons in the DNA genetic code, a codon being a group of several bases (e.g., adenine, guanine, cytosine, or thymine) that denotes a single amino add. 

Until the middle of the eighteenth century, most biologists believed in spontaneous generation—that life arises from combinations of decaying matter, as if flies arose from garbs e. It is now known that DNA genetically codes for many physical characteristics. 

Not only do the I Ching hexagrams correspond to the DNA genetic code [16], but the Ho Tu dots have also been shown to symbolize the molecular structure of the two H-bonded base pairs. The two base pairs are made up of 55 atoms, just like the Ho Tu consists of 55 dots. The dots above the diagonal in Fig. 3 model the cytosine-guanine pair, and those below the diagonal represent adenine-thymine, as drawn. 

Once the broad outlines of DNA replication and protein biosynthesis were established scien tists speculated about how these outlines af fected various origins of life scenarios A key question concerned the fact that proteins are re quired for the synthesis of DNA yet the synthesis of these proteins is coded for by DNA Which came first DNA or proteins How could DNA store genetic infor mation if there were no enzymes to catalyze the polymerization of its nucleotide components How could there be proteins if there were no DNA to code for them ... 

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... 

A potentially general method of identifying a probe is, first, to purify a protein of interest by chromatography (qv) or electrophoresis. Then a partial amino acid sequence of the protein is deterrnined chemically (see Amino acids). The amino acid sequence is used to predict likely short DNA sequences which direct the synthesis of the protein sequence. Because the genetic code uses redundant codons to direct the synthesis of some amino acids, the predicted probe is unlikely to be unique. The least redundant sequence of 25—30 nucleotides is synthesized chemically as a mixture. The mixed probe is used to screen the Hbrary and the identified clones further screened, either with another probe reverse-translated from the known amino acid sequence or by directly sequencing the clones. Whereas not all recombinant clones encode the protein of interest, reiterative screening allows identification of the correct DNA recombinant. 

Vimses are one of the smallest biological entities (except viroids and prions) that carry all the iaformation necessary for thek own reproduction. They are unique, differing from procaryotes and eucaryotes ia that they carry only one type of nucleic acid as genetic material, which can be transported by the vims from one cell to another. Vimses are composed of a shell of proteki enclosing a core of nucleic acid, either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA), that codes for vkal reproduction. The outer shell serves as a protective coat to keep the nucleic acid kitact and safe from enzymatic destmction. In addition to thek proteki coat, some vimses contain an outer covering known as an outer envelope. This outer envelope consists of a Hpid or polysaccharide material. 

RNA structures, compared to the helical motifs that dominate DNA, are quite diverse, assuming various loop conformations in addition to helical structures. This diversity allows RNA molecules to assume a wide variety of tertiary structures with many biological functions beyond the storage and propagation of the genetic code. Examples include transfer RNA, which is involved in the translation of mRNA into proteins, the RNA components of ribosomes, the translation machinery, and catalytic RNA molecules. In addition, it is now known that secondary and tertiary elements of mRNA can act to regulate the translation of its own primary sequence. Such diversity makes RNA a prime area for the study of structure-function relationships to which computational approaches can make a significant contribution. 

If enzymes responsible for DNA repair are unable to remove the DNA adduct, or if an error takes place in the repair, then the error in the genetic code remains when the cell divides. Thus, cellular proliferation is also required, in addition to a mutation, for there to be a permanent effect of a chemical compound. Accumulation of genetic errors, i.e., mutations, has been suspected to be an important factor in chemical carcinogenesis. ... 

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. 

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