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Composition of Nucleic Acids
Nucleic acids are linear polymers, which means that they have a beginning and an end and they consist of repeating monomers called nucleotides. Each nucleotide contains a sugar molecule. In DNA molecules, the sugar is a deoxyribose sugar, which means its missing a hydroxyl group on the 2' carbon atom. In RNA molecules, the sugar is a ribose sugar. The backbone of nucleic acids consist of repeating sugar-phosphate groups that are connected by phosphodiester bonds. A phosphodiester linkage is a connection between the 3' carbon on one sugar molecule and the 5' carbon an adjacent sugar molecule. The presence of a negative charge on the phosphate makes the backbone of the nucleic acid negatively charged and hydrophilic. The sugar molecule is also attached onto the nitrogenous base via the 1' carbon atom. In DNA, the nitrogenous bases are adenine, guanine, cytosine and thymine. In RNA, the thymine is replaced with uracil. Notice that unlike the backbone of the nucleic acids, the bases do not remain constant but change as we move from one nucleotide to the next. Therefore, its the sequence of the bases that determines the genetic code that is stored in the nucleic acid.
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