Final answer:
The substrate of de novo cholesterol synthesis that is the "baby form" of cholesterol is HMG-CoA.
Step-by-step explanation:
The substrate of de novo cholesterol synthesis that is the "baby form" of cholesterol is HMG-CoA (Hydroxymethylglutaryl-CoA). In the process of cholesterol synthesis, two molecules of acetyl-CoA combine to form acetoacetyl-CoA, which then combines with another acetyl-CoA to form HMG-CoA. This HMG-CoA is further processed to eventually form cholesterol.