DNA Replication

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Replication refers to the duplication process of the genetic material. However, in DNA replication, it has been seen that one ‘parental’ double-stranded DNA molecule gets duly converted into two respective identical ‘daughter’ molecules.


DNA Replication

 

Replication refers to the duplication process of the genetic material. However, in DNA replication, it has been seen that one ‘parental’ double-stranded DNA molecule gets duly converted into two respective identical ‘daughter’ molecules. The fundamental basis to understand the DNA replication is the ‘complementary structure’ of the nitrogenous sequences (viz., A, T, C, G) present in the DNA molecule. By virtue of the fact that the predominant bases present along the two strands of double-helical DNA are complementary to each other ; obviously, one strand would precisely act as a ‘tem-plate’** for the critical production of the second strand.

 

Methodology


The DNA replication may be accomplished by adopting the following steps in a sequential manner :

 

(1) First and foremost the presence of ‘complex cellular proteins’ are required essentially which direct a highly specific sequence of events.

 

(2) Once the ‘replication phenomenon’ gains momentum, the two inherent strands of the ‘parental DNA’ get unwounded first, and subsequently separated from each other in ‘one small DNA segment’ after another.

 

(3) Consequently, the ‘free nucleotides’ critically present in the cytoplasm of the cell are duly matched right up to the exposed bases of the single-stranded parental DNA.

 

(4) Importantly, wherever thymine (T) is strategically located on the ‘original strand’, only adenine (A) can easily slot in precisely into place on the ‘new strand’ ; likewise, whenever guanine (G) is duly located on the ‘original strand’, exclusively cytosine (C) may aptly fit into place, and so on so forth.

 

(5) In this entire process, any such ‘bases’ (i.e., A, T, C, G which base-paired improperly are subsequently removed and immediately replaced by the corresponding replication enzymes.

 

(6) Once the ‘aligning process’ has been duly accomplished, the newly incorporated nucleotide gets adequately linked to the growing DNA strand by the aid of an enzyme usually termed as DNA-polymerase.

 

(7) As a result, the parental DNA gets duly unwounded a little further to safely permit the incorporation of the next range of nucleotides. Thus, the ‘critical point’ at which the ‘replication of DNA’ actually takes palce is widely known as the ‘Replication Fork’, as depicted in Figure : 6.1.



 

Explanation of Figure 6.1. The various cardinal points that explain the DNA replication in Fig. 6.1. are as follows :

 

(1) Double helix of the parental DNA gets separated as weak H-bonds between the nucleotides strategically located on opposite strands usually break in response to the action of replica-tion enzymes.

 

(2) H-bonds that critically come into being between new complementary nucleotides and each strand of the parental template to give rise to the formation of the newer base pairs.

 

(3) Enzymes catalyze the formation of sugar-phosphate bonds existing between the sequen-tial nucleotides critically positioned on each resulting daugther strand.

 

It has been duly observed that the ‘replication fork’ mostly moves very much along the parental DNA, whereas each of the unwound single strands strategically combines with new nucleotides. In this way, both these strands, namely : (a) Original strand, and (b) Daugther strand (newly synthesized), get rewound, intimately. As we critically notice that each of the newly formed double-stranded DNA molecule essentially comprise of one original conserved strand and one altogether new strand, the phenomenon of replication under these conditions is invariably termed as semiconservative replication.

 

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