Read for comprehension (not memorization). Dehydration of alcohols is a very significant reaction in biochemistry. For example, after the malonyl group has combined with an acetyl group in fatty acid biosynthesis, a ketone carbonyl is reduced to a hydroxyl group. This hydroxyl group then serves as the site for dehydrogenation. (The vinylic group is then hydrogenated to form an aliphatic chain). Another example of dehydrogenation of alcohols occurs in the citric acid cycle, where the first step in the isomerization of citrate to isocitrate is the dehydration of an alcohol.