![]() ![]() The five-carbon sugar (ribose or deoxyribose) is bound to a nitrogen. This pairing structure keeps the distance between the two backbones of phosphate-linked deoxyribose sugar molecules roughly equal. Both DNA and RNA have a sugar-phosphate backbone that serves as a structural foundation. Specifically, Adenine (A), a purine base, always pairs with Thymine (T), a pyrimidine base, while Guanine (G), a purine base, always pairs with Cytosine (C), a pyrimidine base. A nucleotide is a nucleoside with one or more phosphate groups. This type of bond is called a glycosidic bond. They are all made of a phosphate group, a sugar molecule, and a nitrogenous base. A nucleoside is a base linked to a sugar. The nitrogen bases are pyrimidine in structure and form a bond between their 1 nitrogen and the 1 -OH group of the deoxyribose. The structure of the nucleotides is very similar. The nitrogenous base (guanine in this example) is linked to the 1 carbon of the deoxyribose and the phosphate groups are linked to the 5 carbon. Why is this important? Well 2-rings take up more room than 1-ring, so it helps us make sense of why the bases like to “pair” the way they do. ( A) A nucleotide (guanosine triphosphate). The important difference between these two groups is that purine bases (A & G) have a 2-ring structure, while pyrimidine bases (C & T) have a 1-ring structure. These four bases can be further subdivided into groups of the purine bases (A & G) and the pyrimidine bases (C & T). Attached to each deoxyribose sugar molecule in the DNA backbone is one of four nitrogen-containing bases: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G). These deoxyribose sugar molecules are linked to each other in long chains by their associated phosphate groups, creating the “backbone” of the DNA structure. The nitrogenous base (guanine in this example) is linked to the 1 carbon of the deoxyribose and the phosphate groups are linked to the 5 carbon.
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