Biotin is mainly required as a coenzyme for carboxylation reactions and the main examples are carboxylation of-i) pyruvate to oxaloacetate (first step of gluconeogenesis); ii) Acetyl co A to Malonyl co A (first step of fatty acid synthesis) and iii) Propionyl co A to D-Methyl malonyl co A (in the conversion of propionyl co A to Succinyl co A to gain entry to TCA cycle). In biotin deficiency, out of the given options, defective fatty acid synthesis is the most suited option because of the impaired conversion of acetyl co A to malonyl co A.
The order of successive phosphorylation/ dephosphorylation events starts with the HPr protein, and is followed by Enzyme I, Enzyme IIA and then Enzyme IIB. The only protein that is not phosphorylated is Enzyme IIC. Enzyme IIB-phosphate is the direct phosphoryl-donor to glucose.
The conversion of glucose to glucose-6-phosphate is advantageous to the cell! Since the transported molecule is structurally altered, it can no longer leave the cell via Enzyme IIC. Second, the sugar modification generates the first intermediate of the glycolysis pathway. This saves the expenditure of an additional ATP molecule that would otherwise be needed to make G-6-P from glucose using the glycolysis enzyme, glucokinase.
The structure of cyclocreatine is fairly flat (planar), which aids in passive diffusion across membranes. It has been used with success in an animal study, where mice suffered from a SLC6A8 (creatine transporter at the blood brain barrier) deficiency, which is not responsive to standard creatine supplementation.  This study failed to report increases in creatine stores in the brain, but noted a reduction of mental retardation associated with increased cyclocreatine and phosphorylated cyclocreatine storages.  As demonstrated by this animal study and previous ones, cyclocreatine is bioactive after oral ingestion   and may merely be a creatine mimetic, able to phosphorylate ADP via the creatine kinase system.