![]() DNA or deoxyribonucleic acid is a long molecule in every human that contains their unique genetic code. DNA is a very complex molecule that holds the instructions for making all proteins in our bodies. DNA passes genetic information on from parent to offspring. DNA forms a spiral like structure called a double helix. DNA is made up of four small components that are called nucleotides. These nucleotides are called: adenine (A), cytosine (C), guanine (G), and thymine (T). Adenine pairs with thymine and cytosine pairs with guanine. Nucleotides are made up of three main units: a phosphate group, a nitrogenous base, and a 5-carbon sugar molecule that is called deoxyribose. An organism’s cells passes information on to other cells through a process known as DNA replication. ![]() DNA replication starts with an enzyme called helicase. Helicase breaks the hydrogen bonds that hold the complementary bases together (A, T, C, and G) this causes the double helix to “unzip”. The “unzipped” double helix makes a Y shape which is known as the replication fork. The two separated strands act as templates for making new strands of DNA. One of the strands is positioned in the 3’ to 5’ direction (which is towards the replication fork). This is called the leading strand. The other strand is position in the 5’ to 3’ direction (which is away from the replication fork). This is called the lagging strand. Since the strands are in different orientations, they are replicated differently. For the leading stranding, a short piece of RNA primer, which is produced by an enzyme called primase, comes along and binds to the end of the leading strand. The primer acts as the starting point for DNA synthesis. DNA polymerase binds to the leading strand and then walks along it adding new complementary bases to the strand of DNA in the 5’ to 3’ direction. This type of replication is called continuous. For the lagging strand, many RNA primers are made by the primase enzyme and attach at various points along the lagging strand. Chunks of DNA, known as Okazaki fragments, are added to the lagging strand that are also in the 5’ to 3’ direction. This type of replication is called discontinuous as the Okazaki fragments will need to be joined up later. Once all of the bases are matched up with its corresponding base (A to T and C to G), an enzyme known as exonuclease takes away the primer. The gaps where the primer were are then filled by more complementary nucleotides. The new strand is then proofread to make sure that there are no mistakes in the new DNA sequence. Then, an enzyme known as DNA ligase seals up the sequence of DNA into two continuous double strands. The result of DNA replication is two new DNA molecules that are made up of one new and one old chain of nucleotides. Following replication the new DNA immediately winds up into a double helix. ![]() The structure of DNA allows the DNA replication process to be done easily because of it is easy to unzip the double helix since it is made up of weak hydrogen bonds. The helicase enzyme easily splits through the nucleotides and the ladder-like shape of the DNA allows for nucleotides to be added or taken away easily. The structure of the nucleotides also helps with replication because each base has a corresponding base, thus replication process is very accurate. The DNA replication process is a pretty complex process, but without it, life itself would not continue. Work Cited
Békési, Angéla, and Beáta G Vértessy. “Uracil in DNA: Error or Signal?” Science in School, EIROforum, 3 Mar. 2011, www.scienceinschool.org/2011/issue18/uracil.“DNA Replication.” Brebeuf Jesuit Honors Biotechnology, Edublog, bjpsbiotech.edublogs.org/labs-activities/dna-replication/. Mandal, MD Dr Ananya. “What Is DNA Polymerase?” News Medical Life Sciences, AZO Network, 23 Apr. 2014, www.news-medical.net/life-sciences/What-is-DNA-Polymerase.aspx. Newman, Tim. "What is DNA and how does it work?." Medical News Today. MediLexicon, Intl., 11 Jan. 2018. Web. 30 Jan. 2018. <https://www.medicalnewstoday.com/articles/319818.php> Smith, BPharm Yolanda. “DNA Replication and Repair.” News Medical Life Sciences, AZO Network, 31 May 2017, www.news-medical.net/life-sciences/DNA-Replication-and-Repair.aspx. “What Is DNA Replication?” Your Genome, The Public Engagement Team at the Wellcome Genome Campus, 25 Jan. 2016, www.yourgenome.org/facts/what-is-dna-replication.
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