Nucleophiles and Electrophiles
Reactions of Alcohols and Ethers
Reactions of Carboxylic Acids and Derivatives
Bioenergetics and Cellular Respiration
Integration of Metabolism
|Alcohols can serve as nucleophiles in acyl exchange mechanisms. When the reaction occurs with a carboxylic acid, it is called Fischer esterification, although other carboxylic acid derivatives can also serve as substrates, such as acyl halides or carboxylic acid anhydrides.|
Let us take a moment to look at an important example of esterification in lipid biosynthesis. Glycolysis and the citric acid cycle are important processes not only for bioenergetics but as crossroads in biosynthesis. Glycerol 3-phosphate, an intermediate in glycolysis, contains 3 carbons, two with hydroxyl groups and one with a phosphate ester group. Esterification with the two hydroxyl groups occurs in the process of the condensation of glycerol 3-phosphate and two fatty acids to give phosphatidic acid, a precursor of triglyceride and phospholipid. A further acyl exchange between phosphatidic acid and a fatty acid, replacing the phosphate ester, produces a triglyceride. Direct modification of the phosphate ester portion of phosphatidic acid with choline leads to phospholipid.