Final answer:
A fatty acid must be activated by ATP to form a fatty acyl-coenzyme A (CoA) before it can be attached to a glycerol backbone, as catalyzed by acyl-CoA synthetase.
Step-by-step explanation:
Before a fatty acid can attach to a glycerol backbone, it needs to be activated. This activation involves the fatty acid reacting with ATP. The resulting compound is a fatty acyl-coenzyme A (CoA), which is catalyzed by the enzyme acyl-CoA synthetase. During this process, one molecule of ATP is utilized for each fatty acid molecule, and ATP is converted into adenosine monophosphate (AMP) rather than adenosine diphosphate (ADP). This activation allows the fatty acid to subsequently combine with glycerol to form phosphatidate during the biosynthesis of triacylglycerols.