![]() For the structure of the DNA to be able to twist and be packaged accordingly without bulging and the opposite bases to be able to pair up, a purine has to fit in a pyrimidine. Purines have two rings (see adenine on figure 2) while pyrimidines have one ring. Guanine and adenine are purines while thymine and cytosine are pyrimidines. There are four kinds of nitrogenous bases namely, thymine (T), cytosine (C), adenine (A) and guanine (G). The pentose sugar connects the nitrogenous base to the phosphate backbone. These are crucial to the DNA as they define the genetic code (they are the code!). Image Source: Wikimedia CommonsĪ nitrogenous base is a molecule with nitrogen that possesses the chemical properties of a base. Figure 1: The chemical assembly of the three parts of the nucleotide (in this case adenine), the phosphate (blue box), nitrogenous base (red box) and the pentose sugar. The number of bonds holding nucleotides from the complementary strands depends on the type of nitrogenous base the nucleotide contains. Nucleotides are adjacently strung together through a phosphate backbone and are held together with their complements through hydrogen bonds. Nucleotides simply refer to nitrogenous bases, pentose sugar together with the phosphate backbone. ![]() Nucleic acids are the building blocks of all living organisms. DNA StructureĭNA is a nucleic acid, hinted at in the name. This part of the DNA story is a lot more complex than this, but we will end here for the purpose of this lesson. It is her work together with that of the above-mentioned Nobel Laureates that gave us the gold mine (DNA) that has led to advances in all fields of biology most notably, medicine. Rosalind Franklin captured the famous X-Ray imagery clearly showing its double helical nature. Later on (1869), Friedrich Miescher noted an acidic substance in the cell’s nuclei this substance was referred to as nuclein (we now know this as DNA). In 1866, Gregor Mendel first hypothesized the existence of inherited entities, now known as genes. However, its existence was known of before that. In 1962, Watson, Crick, and Wilkins obtained a Nobel Peace Prize for describing it. The discovery of the structure of DNA opened many avenues in the field of biology. Given how important this structure is, we will also talk about how it is replicated ( DNA replication), packaged, and how these can be exploited or used for DNA fingerprinting. After this, we will then dive into why DNA is so important. Different parts are under different selection pressures.īelow we will outline the history, structure of DNA, the differences and similarities between DNA and RNA. This extremely long double-stranded twisted string has parts that code for everything in all organisms. Two complementary strands of DNA are bonded to each other, and are twisted in a helical structure. These bases are connected to each other through chemical bonds. Stryer L.Simply put, DNA (Deoxyribonucleic Acid) is a string of nitrogenous bases (Adenine, Thymine, Guanine, and Cytosine) repeated over and over, and arranged in a seemingly random fashion. Kilpatrick S.T 2011 Lewin's Genes X, 10th Edition, Jones and Bartlett Publishers: London These two sugars only differ by one -OH group being changed to an -H, but provides different capabilities for each molecule. On on the other hand, the sugar in the backbone of RNA is called ribose. In DNA, the sugar involved is deoxyribose. However, their sugar phosphate backbone differs slightly. RNA and DNA are both examples of phosphodiesters and have a very similar structure. One turn of this helix is 34nm long, the diameter of it is 2nm, and there are ten bases attached per turn at 0.34nm. ![]() These features make DNA can repel water and would not hydrolysed and breakdown by the aqueous environment. DNA is very stable due to rungs of “ladder” is hydrophobic and phosphate sugar backbone of DNA is negatively charged. The purpose of this twisting is to protect the bases inside it, and prevent them from being damaged by the environment. one runs 3' to 5', the other run 5' to 3'. This is done by the sugar phosphate backbone twisting around itself in a coil. Figure 1 Diagram showing the sugar phosphate backbone of DNA, and the nitrogenous bases attached to it, forming a nucleotide Structure of DNAĭNA is wound into an right-handed double helix.
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