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DNA or deoxyribonucleic acid is considered as the blueprint or the hereditary molecule of all living organisms. There are two DNA strands bounded by four nucleotide bases called purines and pyrimidines. The two purines are known as adenine (A) and guanine (G), and the two pyrimides are thymine (T) and cytosine (C). The DNA strands appear as a double helix. They contain the genes and the genetic code which are passed from generations to generations. This is made possible through a process known as DNA Replication. DNA replication therefore, is an essential process in the perpetuation of the species.
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Steps of DNA Replication
DNA replication occurs before cell division and it goes through a series of steps to duplicate new DNA molecules. These steps are as follows:
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Step 1: The Separation of DNA Strands
The steps of DNA replication always begin by separating a twisted strand into two untwisted molecular strands. It happens in the specific area of a chromosome known as the “origins". The origins contain a series of codes that attract the helicase, a protein that aids in the separation of the strands. Once the helicase locates the origins, it sends out signals inside the cell for other replication initiator proteins to help out in the separation. DNA strands are being separated by breaking the hydrogen bonds between the nucleotide base pairs, such as those of adenine (A) and thymine (T), and guanine (G) and cytosine (C).
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Step 2: Replication Fork Formation
Splitting the original double helix into two strands visually presents a Y-shaped formation known as the replication fork. Each prong appears as an elongated line that requires an identical half to match in order to form a new pair of strands. One of the separated strands is called the leading strand, which is constantly utilized for DNA synthesis while the lagging strand is responsible for the complimentary strand’s synthesis.
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Step 3: Binding of Bases to Each Strand
Both leading strand and lagging strand already has base patterns from the start and it serves as the template for the corresponding strands. For each strand, the bases match with the free floating nucleotides present inside the cell following the nucleotide base pairing rules to establish the hydrogen bonding between a separated strand and a new matching strand. It is made possible by the DNA polymerase, an enzyme that functions like a sewing machine in matching and zipping both strands together.
The replication process does not result to a brand new chain of DNA. It is always a mixture of both the original strand that is conserved as a partner all throughout the continuous steps of DNA replication process and the recently made strand. This process is recognized as the semiconservative replication.
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Step 4: The Termination of the Replication Process
The termination process occurs as soon as the DNA polymerase enzyme arrived at the edge of the strands where no more possible replication could occur. But before the process is completed, it goes through the process of repair to correct errors such as mismatching of nucleotides. After this step, the DNA replication is completed.