Proteins are polypeptides. They are linear chains of amino acids linked by peptide bonds.
Unsaturated fatty acids contain one or more double bonds. In a nucleic acid a phosphate moiety links the -carbon of one sugar of one nucleotide to the -carbon of the sugar of the succeeding nucleotide. The bond between the phosphate and hydroxyl group of sugar is an ester bond. As there is one such ester bond on either side, it is called phosphodiester bond. In a polysaccharide the individual monosaccharides are linked by a glycosidic bond. This bond is also formed by dehydration.

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