Replication of DNA Process

Replication of DNA in microbiology is the biological process by which two new identical DNA can be produced from a single original DNA molecule. Such replication can be possible in any living form and is essential for biological inheritance. This process helps in the growth and repair of damaged cells. The double helix of two similar strands is termed DNA. Generally, these two strands exist in a twisted form, but these strands are being separated during the replication process. The individual strand of DNA can provide their respective counterpart, also known as semi-conservative replication. From this semi-conservative, a newly synthesized helix is getting created. 

Millions of Nucleotides form DNA. Deoxyribose sugar, a phosphate, and a base known as nucleobase compose such molecules. Phosphodiester bonds keep each molecule attached. The free 3’—OH of primer RNA provides the initiation point for DNA polymerase, which requires a free 3’—OH of a pre-existing polynucleotide for the initiation of DNA replication. DNA replication is semi-conservative, semi discontinuous, which always occurs in the 5′ —> 3′ direction. Replication of the 3′ —> 5′ strand of a DNA molecule proceeds continuously; therefore, the 3’—>5′ strand of DNA molecule is known as the leading strand. The replication of the 5′ —>3′ strand of the DNA molecule is discontinuous and is known as a lagging strand. Replication of lagging strand generates small nucleotide fragments in 5′ 3′ direction called Okazaki fragments.

The antiparallel strands of the DNA are being connected via four types of bases: Cytosine, Guanine, Adenine, and Thymine. Generally, cytosine binds or connects to guanine, while adenine binds with thymine.

DNA Replication steps

There lie three steps for the DNA replication process: initiation, elongation, and termination.

• Initiation:

From a particular point, this initiation or process starts so that a specific coding place is generally termed as ‘origin.’ Proteins generally initiate this process and start attracting more of them, giving rise to the processing of new replication DNA from the original DNA molecule. Many spots give rise to the initiation of this process; such sites or spots are referred to as replication forks. 

Inside this replication complex lies an enzyme named DNA helicase, which helps unwind the strands of DNA, and thus this makes the process much easier for replication of the original DNA molecule. This enzyme breaks the bond of two strands by creating a bond with nucleobases.

Another enzyme that also helps in initiating this replication process is DNA primase. This enzyme synthesis a small RNA primer and thus help in the expansion of the strands in the new replicated DNA molecule.

• Elongation

The processor synthesis will start as soon as DNA Polymerase attaches itself with double unzipped strands. The polymerase will enhance itself by adding free nucleotides to the third carbon atom, also known as 3′. If the original strand is recognized as 3′ to 5′, then for the new one, which is a mirror image of the DNA molecule, the strand will be recognized as 5′ to 3′. 

The newly formed strand is also known as the leading strand, and with this strand, only DNA Primase is needed to react with RNA Primer, which initiates the DNA polymerase. This polymerase helps extend the 3′ to 5′ direction strand concerning its antiparallel one.

The 3′ to 5′ direction strand is known as the leading strand, while the antiparallel of this strand, which is 5′ to 3′ direction, is generally termed a lagging strand. DNA polymerase process opens or rather unwinds the helix structure and exposes the bases of the molecules, which lead to synthesis in fragments, and such fragments are termed as Okazaki fragments.

• Termination

Termination is the last stage or step of the DNA replication process, and in this process, the strands get expanded and converted into two replication forks. The termination process generally happens randomly and will not stop until the total separation occurs. 

Once this process gets finished, the newly formed strands are bounded and stabilized. For the lagging strand, the two most important enzymes RNAase H and DNA ligase, play an important role as one helps initiate Okazaki fragments. In contrast, the other helps in joining the fragment together.

The DNA replication occurs during:

In the preparatory phase of the cell cycle, DNA replication takes place. Mainly this activity or process gets initiated during the S phase, which is part of the interphase of the cell cycle.

DNA replication generally occurs in the interphase stage of the cell cycle. In the synthetic phase of interphase, the DNA replicates, and histone protein synthesis occurs. The centrioles also get duplicated.

Conclusion

Replication of DNA in microbiology is the biological process by which two new identical DNA can be produced from a single original DNA molecule. Such replication can be possible in any living form and is essential for biological inheritance. This process helps in the growth and repair of damaged cells.DNA replication takes place during the S-phase of interphase in the cell cycle. DNA replication is a semi-conservative process. DNA is the only molecule capable of self-duplication, so it is termed a living molecule. All living beings have the capacity to reproduce because of DNA.   

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