Editing Biomolecule (section)

==Lignin==
[[Lignin]] is a complex polyphenolic macromolecule composed mainly of beta-O4-aryl linkages. After cellulose, lignin is the second most abundant biopolymer and is one of the primary structural components of most plants. It contains subunits derived from [[paracoumaryl alcohol|''p''-coumaryl alcohol]], [[coniferyl alcohol]], and [[sinapyl alcohol]],<ref>{{cite book |editor= K. Freudenberg |editor2=A.C. Nash |year=1968 |title=Constitution and Biosynthesis of Lignin |location=Berlin |publisher=Springer-Verlag}}</ref> and is unusual among biomolecules in that it is [[racemic]]. The lack of optical activity is due to the polymerization of lignin which occurs via [[radical (chemistry)|free radical]] coupling reactions in which there is no preference for either configuration at a [[chirality (chemistry)|chiral center]].