Why does DNA need to be replicated? DNA must be replicated to form identical daughter cells. If DNA replication enables four chromosomes, it can divide into two cells, each with two chromosomes. Helicase defrosts and rewinds the DNA double helix by breaking hydrogen bonds.
DNA replication is required because existing cells divide to produce new cells. A complete instruction manual is required for each cell to function properly. Therefore, it is necessary to copy the DNA before cell division to give complete instructions to each new cell.
What if the DNA is not replicated?
DNA replication occurs during the synthetic phase of the cell cycle. Without DNA replication, the cell cycle does not advance to the next stage and no further division occurs. It leads to cell death.
Brief description of Why does DNA need to be replicated
DNA replication is the process of copying a double-stranded DNA molecule to produce two identical DNA molecules. Replication is an essential process because whenever a cell divides, the two new daughter cells must contain the same genetic information or DNA as the parent cell. The replication process relies on the fact that any strand of DNA can act as a template for replication.
DNA replication begins at a specific point called the origin of the DNA double helix unraveling. A short segment of RNA, called a primer, is then synthesized and serves as a starting point for new DNA synthesis. An enzyme called DNA polymerase then initiates DNA replication by matching the base to the original strand. When synthesis is complete, the RNA primers are replaced with DNA and the gaps between the newly synthesized DNA segments are enzymatically closed.
DNA replication is an important process. Therefore, the cell calibrates the newly synthesized DNA to prevent the introduction of errors and mutations. When the DNA in a cell is replicated, the cell is split into two cells, each with the same copy of the original DNA.
So, beside of the quiz of why does DNA need to be replicated, this’is a review about the process of DNA replication.
5 Steps of DNA Replication
The explanation below is the stages of DNA replication. An explanation that tries to answer of why does DNA need to be replicated?
Step 1: Before replicating the DNA that forms the replication fork
The double-stranded molecule must be “thawed” into two single strands. DNA has four bases called adenine (A), thymine (T), cytosine (C), and guanine (G), which form a pair between two strands. Adenine is paired only with thymine and cytosine is paired only with guanine. In order for DNA to unravel, it is necessary to break these interactions between base pairs. This is done by an enzyme known as DNA helicase. DNA helicase breaks hydrogen bonds between base pairs and separates the strands into a Y-shape called a replication fork. This area serves as a template for initiating replication.
DNA is oriented on both strands and is characterized by 5’and 3’ends. This notation indicates which side group is attached to the DNA backbone. The phosphate group (P) is attached to the 5’end and the hydroxyl group (OH) is attached to the 3’end. This direction is important for replication as it only progresses in the 5’to 3’direction. However, the replication fork is bidirectional. One strand is directed from 3’to 5′(leading strand) and the other strand is directed from 5’to 3′(lagging strand). Therefore, the two sides are duplicated using two different processes to compensate for the difference in orientation.
Step 2: Primer binding
Leading strands are the easiest to replicate. When the DNA strand is separated, a short RNA called a primer attaches to the 3’end of the strand. The primer always binds as the starting point of replication. Primers are produced by the enzyme DNA primase.
Step 3: The Elongation
Enzyme, known as DNA polymerase, is responsible for creating new strands through a process called Elongation. Bacterial and human cells have five different and known types of DNA polymerases. In bacteria such as E. coli, polymerase III is the major replication enzyme, and polymerases I, II, IV, and V are involved in error checking and recovery. DNA polymerase III binds to the strand at the primer site and initiates the addition of new base pairs complementary to the strand during replication. In eukaryotic cells, polymerase alpha, delta, and epsilon are the major polymerases involved in DNA replication. The newly formed strands are continuous because replication occurs in the leading strand in the 5’to 3’direction. The
Delayed strand initiates replication by binding to multiple primers. The primers are only a few bases apart. Next, DNA polymerase adds fragments of DNA, so-called Okazaki fragments, to the strands between the primers. This replication process is discontinuous because the newly created fragment is isolated.
Step 4: Termination
When both continuous and discontinuous strands are formed, an enzyme called an exonuclease removes all RNA primers from the original strand. These primers are then replaced with the appropriate bases. Another exonuclease “corrects” the newly formed DNA to check, remove, and replace errors. Another enzyme, called DNA ligase, binds Okazaki fragments to a single unified strand. The ends of linear DNA cause problems because DNA polymerase can only add nucleotides in the 5’to 3’direction.
The ends of the parent strand are composed of repeating sequences of DNA called telomeres. Telomeres act as protective caps at the ends of chromosomes to prevent adjacent chromosomes from fusing. A special type of DNA polymerase enzyme called telomerase catalyzes the synthesis of telomere sequences at the ends of DNA. When complete, the DNA of the parent strand and its complementary strand will be in the familiar double helix form. Finally, replication produces two DNA molecules, each having a chain of the parent molecule and a new chain.
Step 5: Replication Enzyme
DNA replication will not occur without enzymes that catalyze different steps in the process. Enzymes involved in the eukaryotic DNA replication process include:
- DNA helicases, and double stranded DNA is separated when moved along DNA. It forms a replication fork by destroying the hydrogen bond between the nucleotide pairs in the DNA.
- RNA primer producing DNA Priasase A RNA polymerase. Primers are short RNA molecules that serve as templates for DNA replication start.
- DNA polymerase synthesizes new DNA molecules by adding nucleotides to the leading and lag strands of DNA.
- Topoisomerase or DNA gyrase rewinds and rewinds DNA strands, preventing DNA from becoming entangled or supercoiled.
- Exonuclease A group of enzymes that remove nucleotide bases from the ends of DNA strands.
- DNA ligase binds DNA fragments by forming phosphodiester bonds between nucleotides.
Summary of DNA Replication
DNA replication is the production of the same DNA helix from a single double-stranded DNA molecule. Each molecule consists of a strand of the original molecule and a newly formed strand. Prior to replication, the DNA is unwound and the strands are separated. A replication fork is formed that acts as a replication template. The primer binds to the DNA and the DNA polymerase adds a new nucleotide sequence in the 5’to 3’direction.
This addition is continuous with leading strands and fragmented with lagging strands. When the DNA strand has been stretched, the strand error is checked, repaired, and the telomere sequence is added to the end of the DNA. So, the answer of why does DNA need to be replicated, clearly.
