The structure of a fat, or triacylglycerol. The molecular building blocks of a fat are one molecule of glycerol and three molecules of fatty acids. (a) One water molecule is removed for Each fatty acid is joined to the glycerol by dehydration. The removal of a hydroxyl (-OH) from the carboxyl group at the end of the fatty acid results in a form of catbobyl called an acyl group, and the fat molecule is called triacylglycerol, or more commonly triglyceride.