Why isn't acetyl-coA an entry point for gluconeogenesis?
The problem is that acetyl-CoA enters the TCA cycle by condensing with oxaloacetate in the citrate synthase reaction. Therefore, you need 1 oxaloacetate for each acetyl-CoA added. Now, if the citrate formed goes on to oxaloacetate which is then removed for gluconeogenesis, there is no oxalocatete left for the next citrate synthase reaction. The reactions do not balance. Therefore, an anaplerotic substrate like glutamine or asparate is needed to replenish the lost oxaloacetate.