Here is your short paragraph on DNA : a genetic material.
As DNA is a genetic material, it carries genetic information’s from cell to cell and from generation to generation.
At this stage, an attempt will be made to determine that in what manner the genetic information’s are existed in DNA molecule? Are they written in articulated or coded language on DNA molecule? If in the language of codes what is the nature of genetic code?
A DNA molecule is composed of three kinds of moieties: (i) phosphoric acid, (ii) deoxyribose sugar, and (iii) nitrogen bases. The genetic information’s may be written in any one of the three moieties of DNA. But the poly-sugar-phosphate backbone is always the same, and it is, therefore, unlikely that these moieties of DNA molecule carry the genetic information’s. The nitrogen bases, however, vary from one segment of DNA to another, so the information’s might well depend on their sequences.
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The sequences of nitrogen bases of a given segment of DNA molecules, actually, has been found to be identical to linear sequence of amino acids in a protein molecule. The proof of such a colinearity between DNA nitrogen base sequence and amino acid sequence in protein molecules has first obtained from an analysis of mutants of head protein of bacteriophage T4 and the A protein of tryptophan synthetase of Escherichia coli. The colinearity of protein molecules and DNA polynucleotides has given the clue that the specific arrangement of four nitrogen bases (e.g., A, T, C and G) in DNA polynucleotide chains, somehow, determines the sequence of amino acids in protein molecules.
Therefore, these four DNA bases can be considered as four alphabets of DNA molecule. All the genetic information’s, therefore, should be written by these four alphabets of DNA. Now the question arises that whether the genetic information’s are written in articulated language or coded language? If genetic information’s might have occurred in an articulated language, the DNA molecule might require various alphabets, a complex system of grammar and ample amount of space on it.
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All of which might be practically impossible and troublesome too for the DNA. Therefore, it was safe to conclude for molecular biologists that genetic information’s were existed in DNA molecule in the form of certain special language of code words which might utilize the four nitrogen bases of DNA for its symbols. Any coded message is commonly called cryptogram.