Unlike proteins, which have 20 different kinds of amino acids, there are only 4 different kinds of nucleotides in nucleic acids. Like proteins, nucleic acids have a primary structure that is defined as the sequence of their nucleotides. A similar segment of RNA would have OH groups on each C2′, and uracil would replace thymine. This is why these compounds are known as nucleic acids.įigure 14.2.
The purine and pyrimidine bases branch off this backbone.Įach phosphate group has one acidic hydrogen atom that is ionized at physiological pH. The backbone of the chain consists of alternating phosphate and sugar units (2-deoxyribose in DNA and ribose in RNA). This unit joins to a third nucleotide, and the process is repeated to produce a long nucleic acid chain (Figure 14.2.1). Nucleotides are joined together through the phosphate group of one nucleotide connecting in an ester linkage to the OH group on the third carbon atom of the sugar unit of a second nucleotide.
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