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DNA replication can be explained as the process of making copies of the DNA in a living cell before its division occurs. DNA acts as a manual to operate how a living organism will function. DNA is a ladder, that is twisted into a spiral. Each side of the ladder has molecules attached to it known as nucleotides. These nucleotides are present in the paired form. They are usually present as A, T, G, and C.
These are found in a puzzled-together fashion like a puzzle: A with T and G with C. The whole process of DNA copying is like opening the twisted ladder, making copies of each side, and then arranging them back together.
Why Does DNA Replicate?
DNA replication is important for cells to grow, reproduce, and function well. To function properly, each new cell requires an exact copy of the DNA. This ensures that each cell receives an identical set of instructions for protein synthesis and other activities. DNA replication is the process by which a cell ensures that its instructions are accurately copied for new cells. The replication of DNA ensures that each cells in the body have the same genetic instructions.
What are the steps in DNA replication?
DNA replication occurs in three easy steps. To put it simply, the DNA strands are unzipped, and new strands are built using enzymes. Lastly, the two identical DNA copies are completed. The steps are mentioned below for a better understanding.
Initiation
DNA replication requires a high level of accuracy since even small errors can result in mutations. As a result, replication cannot start randomly at any position in DNA. There is a particular region where replication begins. This is where replication begins. After this origin has been spotted, the two DNA strands are unwound and replication begins. The region is known as the origin of replication.
In this process, the DNA strands are unzipped into two strands. It results in breaking the bonds between nucleotides. This is done with the help of an enzyme called helicase. This creates a Y-shaped region, also known as a replicating fork.
Elongation
After the unwinding process, we have two strands of DNA that require to be copied. The enzyme DNA polymerase helps add a nucleotide to these newly formed strands in the ATGC fashion of pairing. To understand it better, if the old strand has an A, the new strand will get a T. Likewise, if the old strand has a G, the new strand will get a C.
During elongation, DNA is always polymerized in a 5′ to 3′ direction only, i.e. elongation is unidirectional. Since DNA can be copied in one direction, the lagging strand can be copied with ease. This is because the leading strand is synthesized in the same direction as the replicating fork.
But, in the case of a lagging strand, the DNA copy will occur in pieces and as it faces the opposite direction. These fragments are also called Okazaki fragments. The Okazaki fragments are further glued together by enzyme ligase. The next step involves checking for any possible error by DNA polymerase. It checks if any wrong nucleotide isn’t added to the strand by mistake.
Termination
After the addition of nucleotides, the enzyme DNA ligase seals everything. Ligase joins the Okazaki fragments together and ensures that the new DNA strands are tightly bound. The replication process is terminated in different ways depending on the organism. It is common for E. coli-like organisms to have circular chromosomes. In this case, the two replication forks connect at both terminals.
Role of Enzymes in DNA Replication
There are different enzymes that work in the DNA replication process. Mentioned below are the enzymes involved in the DNA replication process.
- Helicase – This enzyme is responsible for unwinding the DNA structure, which is twisted ladder-like. It separates the two strands of the DNA double helix, making an open area for copying DNA.
- Primase – Primase introduces a short piece of RNA known as a primer. This primer serves as a starting point for the DNA polymerase to begin copying.
- DNA Polymerase – DNA polymerase is the most important enzyme. It adds additional nucleotides to the increasing DNA strand, ensuring that the new strand matches the old (A with T, G with C).
- Ligase – It helps in sticking the fragments and pieces of DNA. It occurs mainly in the lagging strand and ensures that all the pieces are intact.
- Topoisomerase – This enzyme prevents the strands from tangling into one another, as it is being unwound.
What is semi-conservative replication?
DNA is copied using semi-conservative replication. This process results in two strands of DNA being formed from the original DNA and one from the new DNA.
- As a result, after replication, both DNA copies are half “old” and half “new.”
- For the new DNA to be accurate and match the original, it keeps one of the original strands.
- When DNA is copied using this method, genetic stability is maintained and major errors are prevented.
The DNA polymerase enzyme adds nucleotides to each template strand by matching bases (A matches T and G matches C). Each new DNA molecule conserves half of the original DNA, which is why it is called “semi-conservative.”
FAQs on DNA Replication
What is DNA replication?
DNA replication is the process by which a cell produces an exact copy of its DNA. This happens before a cell splits, making sure that each new cell has the same genetic material. DNA replication is important for cells to grow, reproduce, and function well.
When does DNA replication occur?
DNA replication occurs during the S phase of a cell's life cycle. This is the time when the cell replicates all the DNAs. During the S phase, the cells make sure that the newly formed cells have the same number of DNA.
What enzymes are involved in DNA replication?
The enzymes involved in DNA replication are - helicase, responsible for unwinding the DNA strands. DNA polymerase adds new nucleotide the growing strand of DNA. Ligase joins the okazaki fragments on the lagging strand of DNA.
What is the difference between the leading and lagging strands?
The leading strand is synthesized in the same direction as the replicating fork. Whereas, the lagging strand is synthesized in small fragments also known as Okazaki fragments. They are synthesized in opposite directions, which are later joined by ligase
What is a replication fork?
The replication fork is described as a Y-shaped region. It is a place where DNA is split into two strands, and replication occurs. It is formed when the double helix of DNA gets pulled apart by the helicase enzyme.
