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Nucleic acids
Organisms store information about the structures of their proteins
in macromolecules called nucleic acids. Nucleic acids are long polymers
of repeating subunits called nucleotides. Each nucleotide is made
up of three smaller building blocks (Figure 17):
Figure 17 The structure of a nucleotide and the formation
of nucleic acid chains. As shown in the inset, a nucleotide is composed
of a five carbon sugar, a phosphate group, and an organic nitrogen
base. The sugar and phosphate groups make up the back bone of a nucleic
adic chain, while the nitrogenous bases link the two sides of the
chain. the five nitrogen bases that occur in the nucleic acids of
DNA and RNA are shown on the right.
1. A five-carbon sugar
2. A phosphate group (-PO4-2)
3. An organic, nitrogen-containing molecule called a base
To form the nucleic acid chain, the
sugars and phosphate groups making up the nucleotides are linked;
a nitrogenous base protrudes from each sugar as shown in Figure 17.
The order in which the nucleotides are linked together forms a code
that ultimately specifies the order of amino acids in a particular
protein.
Organisms have two forms of nucleic
acid. One form, deoxyribonucleic acid (DNA), stores the information
for making proteins. The other form, ribonucleic acid (RNA), directs
the production of proteins.
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