The mantle is a layer of the Earth between the crust and the core. The upper mantle starts below the crust and goes down to a depth of around 200 miles to the boundary with the lower mantle.The temperature of the mantle ranges from 900 degrees Fahrenheit near the crust to as high as 7000 degrees near the core.he center of the earth is the core and it is solid, kind of like the pit in a peach. The outer layer of the Earth is called the crust and is thin, like the skin of the peach. In between the two, in the meat of the peach, is the mantle, which can further be divided into the upper and lower mantle.
The bases themselves are classified into two groups known as purines (adenine and guanine) and pyrimidines (cytosine and thymine). Albeit slightly on a different note, RNA (RiboNucleic Acid) incorporates a fifth base known as uracil (U) which takes the place of thymine within the functional RNA structure.
Figure 1: The chemical structure of a nucleotide. A single nucleotide is made up of three components: a nitrogen-containing base, a five-carbon sugar, and a phosphate group. The nitrogenous base is either a purine or a pyrimidine. The five-carbon sugar is either a ribose (in RNA) or a deoxyribose (in DNA) . Â© 2013 Nature Education All rights reserved.