DNA Replication

DNA replicates semi-conservatively and is aided by a series of enzymes. Let us look at the DNA replication process and the enzymes that play a role in it.

DNA Replication is the natural process of producing two identical copies of DNA from a single unique DNA molecule. The most important aspect of organic legacy is DNA replication, which brings everything together in living species. This is necessary for cell division during the development and repair of damaged tissues and to ensure that each new cell has its own copy of the DNA. 

The parental DNA stays together and the newly formed daughter strands stay together in conservative replication. Each of the two parental DNA strands serves as a blueprint for new DNA integration in the semi-conservative method; following replication, each two-fold abandoned DNA incorporates one parental or “old” strand and one “new” strand.

Stages of DNA Replication

Here’s the DNA Replication classification: 

Initiation

DNA synthesis begins at certain locations along the DNA strand, referred to as ‘origins,’ which are found within the replication complex. DNA helicase is an enzyme that unwinds the double-helical structure and exposes each of the two strands so that they can be used as replication templates. Hydrolysing is the method used. The ATP is utilized to disrupt the connections that hold the two strands together by forming bonds between the nitrogen bases.

Another enzyme involved in DNA replication is DNA Primase. It produces a tiny RNA primer that serves as a kickstarter for the DNA polymerase enzyme. The enzyme DNA polymerase is entirely responsible for forming and growing new strands of DNA-specific coding regions.

Elongation

The DNA polymerase can begin the synthesis of new DNA to match the templates once it has linked to the original and unzipped the two strands of parental DNA (i.e., the template strands). It is noteworthy that DNA polymerase can only expand the primer by adding free nucleotides to the 3′ end, not the 5′ end. During replication, RNA primers are added to the newly exposed bases on the lagging strand and DNA synthesis occurs in fragments but in the same 5′ to 3′ direction as before. Okazaki fragments are the name for these fragments.

Termination

The act of extending new DNA strands continues until either no more DNA template is available for replication (i.e., at the chromosome’s end) or two replication forks meet and terminate. The meeting of two replication forks is uncontrolled and occurs randomly throughout the chromosome’s length.

Following the completion of DNA synthesis, the newly produced strands must be bonded and stabilized. Two enzymes are required to achieve this stable stage in the lagging strand. The RNAse enzyme removes the RNA primer from the start of each Okazaki fragment and the DNA Ligase enzyme connects the fragments to form a full strand.

Role of enzymes in DNA Replication

The process of DNA Replication is heavily reliant on enzymes. Many enzymes are involved in DNA replication, including DNA-dependent DNA polymerase, helicase, ligase etc. The principal enzyme among them is DNA-dependent DNA polymerase.

DNA-dependent DNA polymerase

With the help of other enzymes, it aids in polymerisation, catalyses and regulates the entire process of DNA replication. The replication process uses deoxyribonucleoside triphosphates as both a substrate and an energy source. There are three types of DNA polymerase:

DNA Polymerase I

It’s a DNA-repair protein. It participates in three different activities:

• Activity of the 5′-3′ polymerase
• Activity of the 5′-3′ exonuclease
• Activity of 3′-5′ exonuclease

DNA Polymerase II

Primer extension and proofreading are its responsibilities.

DNA Polymerase III

It is in charge of in-vivo DNA replication.

Enzymes used in replication

Helicase

Helicase is an enzyme that breakdowns the bonds of hydrogen between DNA strands to unzip them. As a result, it contributes to the formation of the replication fork.

Ligase

Ligase helps to bind the broken DNA strands together.

Primase

This enzyme aids in the production of RNA primers that complement the DNA template strand.

Endonucleases

In a DNA molecule, this results in a single or double-stranded cut. 

DNA Replication process in prokaryotes

In prokaryotes, DNA replication takes place in the following location:

At the replication origin, the two strands of DNA unwind.

The helicase opens the DNA, forming replication forks.

Single-strand binding proteins cover the DNA around the replication fork to prevent it from rewinding.

Topoisomerase stops DNA from supercoiling.

• Primase is the enzyme that makes RNA primers. The DNA strand is complementary to these primers.
• At the end of the primers, DNA polymerase III begins adding nucleotides.
• Both the leading and trailing strands are lengthening.
• After removing the primers, the gaps are filled with DNA Polymerase I; ligase is used to seal them.

DNA Replication process in eukaryotes

The replication of DNA in eukaryotes is comparable to that of prokaryotes. However, the initiation process in eukaryotes is more complicated than in prokaryotes. Multiple replication sources can be found in eukaryotes. Other initiator proteins form a pre-replication complex. Although the procedure is identical, the enzymes used are not. The polymerization process in eukaryotes is carried out by the enzyme Pol I, whereas in prokaryotes, it is carried out by DNA Pol III.

Conclusion 

The most important aspect of organic legacy is DNA Replication, which brings everything together in living species. DNA Replication is the natural process of producing two identical copies of DNA from a single unique DNA molecule.