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Biological & Biomedical Sciences
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Deoxyribonucleic Acid Replication Essay (Essay Sample)

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the task was about the DNA replication steps

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DNA Replication
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Deoxyribonucleic Acid Replication
Replication refers to a process by which a double-stranded DNA molecule gets copied to generate two duplicate molecules. Deoxyribonucleic acid is the hereditary material responsible for defining each cell. Before the duplication and division of a cell into new daughter cells either via meiosis or mitosis, organelles and biomolecules must get reproduced to be dispensed amongst the cells. In order to make sure that every novel cell gets the right number of chromosomes, replication must be initiated. The replication processes involves numerous proteins and steps, and the process is vital for the repair of the cell, its growth as well as reproduction in organisms. DNA replication takes place in three major steps, which entail initiation, elongation, and termination.
Structure of Deoxyribonucleic Acid
Deoxyribonucleic acid is comprised of molecules referred to as nucleotides. Each nucleotide is endowed with a nitrogen base, a sugar group and a phosphate group. There are four types of nitrogen bases, namely, thymine (T), adenine (A), cytosine (C), and guanine (G). The genetic code is determined by order of the nitrogen bases (Goswami et al., 2018). In order to come up with a double helix structure, nucleotides are attached together, thus forming two long strands. The double helix forms a ladder-like structure with the sugar and phosphate molecules at the sides, whereas the nitrogen bases form the rungs—the nitrogen bases on one strand pairs with the other strand's nitrogen bases. Guanine pairs with cytosine, while adenine pairs with guanine. Because deoxyribonucleic acid molecules are long in nature, they are tightly coiled to form chromosomes so that they can fit inside the cell. Each chromosome is made up of a single deoxyribonucleic acid.
Formation of Replication Fork
Before the replication of DNA can take place, the double-stranded helix must be “unzipped” into double distinct strands. DNA helicase is responsible for breaking the interactions between the base pairs. The enzyme does this by disrupting the hydrogen bonds amid the pairs leading to a replication fork formation. The replication fork acts as the template for replication to commence. In both strands, deoxyribonucleic acid directions is signified by 5’ and 3’ end. The 3’ end has an OH group (hydroxyl group) attached to it, while the other end is attached to a phosphate group. Replication advances in the 5' to 3' direction. Nevertheless, the replication fork is bi-directional, with the orientation of the leading strand being in the 3' to 5' direction, whereas that of the lagging strand is 5' to 3'. In order to house the directional dissimilarity, both sides get replicated with two varied procedures.
The figure below showcases deoxyribonucleic acid replication fork (Topics, 2021).
Initiation
Deoxyribonucleic acid synthesis gets instigated at specific coding regions within the DNA referred to as 'origins.' These regions are targeted by the initiator proteins, which go ahead and employ more proteins that assist in the deoxyribonucleic acid replication procedure, thus establishing a replication complex around deoxyribonucleic acid’s origin (Riera et al., 2017). As compared to prokaryotes that have one origin of replication, eukaryotes have multiple replication origins. Replication commences when the origin-binding proteins bind to the deoxyribonucleic acid’s origin of replication. Enzyme helicase foresees the unwinding of the double helix by breaking hydrogen bonds, thus generating a replication fork. The leading and lagging strands are formed from the replication fork. According to Martin & Wood (2019), the unwound deoxyribonucleic acid is stabilized by stranded binding proteins, and this prevents it from forming secondary structures. Secondary structures can prevent deoxyribonucleic acid polymerase's continuation.
Elongation
Upon the DNA polymerase attachment to the origins, it is now able to begin synthesizing the novel deoxyribonucleic acid to match the templates. Topoisomerases are responsible for reducing the pressure on the winding portions and continuing to open the deoxyribonucleic acid downstream to allow for elongation. Topoisomerases work by changing the amount of deoxyribonucleic acid by unlinking DNA circles for prokaryotic DNA or adding negative supercoils (Chaudhry & Khaddour, 2020). Once the double helix is open, a base is needed for the deoxyribonucleic acid to bind to and start replication. It is important to note that deoxyribonucleic acid polymerase can only prolong the primer through the addition of free nucleotides to the 3’ end. Since one of the templates is recited in the 3’ to 5’ direction, the leading strand will be generated in a 5’ to 3’ direction.
Deoxyribonucleic acid primase only needs to synthesize a ribonucleic acid primer once along the leading strand. It does so at the beginning in order to initiate deoxyribonucleic acid polymerase. The reason being, the new DNA can be prolonged by DNA polymerase by reading the 3' to 5' template, synthesizing in a 5’ to 3’ direction. Nevertheless, the lagging strand is read in the 5’ to 3’ direction because it is anti-parallel. As in the leading strand, continuous deoxyribonucleic acid synthesis would need to be 3’ to 5’ direction (Chaudhry & Khaddour, 2020). This is impossible mainly because bases cannot be added to the 5’ end. In its place, as the double helix unties, the ribonucleic acid primers get added to the recently uncovered nitrogen bases on the lagging strand, and the deoxyribonucleic acid synthesis takes place in the 5’ to 3’ d

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