Any of several complex compounds occurring in living cells, usually chemically bound to proteins to form nucleoproteins. Nucleic acids are of high molecular weight are easily changed by many mild chemical reagents. They contain carbon, hydrogen, oxygen, nitrogen (15–16%), and phosphorus (9–10%).The fundamental units of nucleic acid, are nucleotides, nucleic acids, and polynucleotides in which the nucleotides are linked by phosphate bridges. Upon extensive heating in the presence of water (hydrolysis), nucleic acids yield a mixture of purines and pyrimidines, d-ribose or d-deoxyribose, and phosphoric acid. Nucleic acids are subdivided into two types: ribonucleic acid (RNA), containing the sugar d-ribose, and deoxyribonucleic acid (DNA), containing the sugar d-deoxyribose. See Deoxyribonucleic Acid; Ribonucleic Acid; Nucleoside; Nucleotide; Nucleoprotein. Good sources of nucleic acids are salmon, thymus, yeast, and wheat kernel embryo.