Structure and Function of Genetic Material

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Chapter: Pharmaceutical Microbiology : Microbial Genetics and Variations

DNA constitute an integral component of genes**, whereas, nucleotides designate a macro-molecule made up of repeatable units present in DNA.

Structure and Function of Genetic Material


DNA constitute an integral component of genes**, whereas, nucleotides designate a macro-molecule made up of repeatable units present in DNA. In fact, each nucleotide essentially comprises of a ‘nitrogenous base’ viz., adenine (A), thymine (T), cytosine (C), and guanine(G) — besides, a pentose sugar deoxyribose, together with a ‘phosphate’ moiety. It has been duly established that within a cell the DNA is invariably present as ‘long strands of nucleotides that are duly twisted together in pairs to form a double-helix’.***


Each strand of DNA prominently bears two structural features, namely :


(a) a string of alternating sugar and phosphate moieties, and


(b) a nitrogenous base attached duly to each sugar moiety in its backbone.


Thus, the ‘pair of strands’ are intimately held together strategically by means of H-bonds be-tween their respective nitrogenous bases. However, the ‘pairing of nitrogenous bases’ are found to be in a specific manner i.e., adenine pairs with thymine ; and cytosine pairs with guanine [either AT or CG pairs]. Due to this specific base pairing mode, the base sequence of one DNA strand categorically determines the base sequence of the other strand. Therefore, one may observe that the strands of DNA are actually complementary.**** It has already been proved and established that the aforesaid ‘com-plementary structure of DNA’ goes a long way to expatiate as well as explain the manner by which the DNA actually stores and critically transmits the so called ‘genetic information’.


The functional product is invariably a messenger RNA (designated as mRNA) molecule, that eventually results in the formation of a protein. Interestingly, it may also be a ribosomal RNA (i.e., rRNA). It is, however, pertinent to state here that both these types of RNA (viz., mRNA and rRNA) are prominently involved in the process of protein synthesis.


Genetic Code : It has been duly ascertained that relevant ‘genetic information’ is meticulously encoded by the sequence of bases along a specific strand of DNA, which is almost similar to the usage of ‘linear sequence of alphabets’ to first construct ‘words’, and secondly, the ‘sentences’. Impor-tantly, the so called ‘genetic language’ largely makes use of only four letters viz., A, T, C and G (representing 4-amino acids). However, 1000 of the aforesaid four bases, the number usually contained in an average gene, may be conveniently arranged upto 41000 different variants. Therefore, the usual ‘genetic manipulation’ can be accomplished successfully to provide all the ‘necessary vital informa-tions’ a cell essentially requires for its growth and deliver its effective functions based on the astronomi-cal huge number gene variants. In short, the ‘genetic code’ overwhelmingly determines the intricacies of a nucleotide sequence for its conversion into the corresponding amino acid sequence of a particular protein structure.


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