<prompt> Biotin is needed inKrebs cycleUrea cycleFatty acid synthesisPyruvate dehydrogenase  <response>: Biotin acts as co- enzymes for carboxylation reactions .Bioitin captures a molecule of CO2 which is attached to nitrogen of biotin molecule.Energy required for this reaction is provided by ATP.Tgen activated carboxyl group is transferred to the substrate.Biotin requiring CO2 Fixation reactions. Acetyl CoA CO2 ATPMethyl malonyl CoA ADP Pi This is the rate limiting reaction in fattyacid synthesis. Propionyl CoA CO2 ATP Methyl malonyl CoA ADP Pi In oxidation of odd chain fatty acids. Pyruvate CO2 ATP Oxaloacetate ADP Pi Oxaloacetate acts as catalyst for TCA cycle and as enzyme in gluconeogenic pathway Reference: DM.VASUDEVAN.TEXTBOOK SEVENTH EDITION page no 485 Co-enzyme Main reaction using the co -enzyme Group transferred Thiamine pyrophosphateTPP oxidativedecarcoxylation of alpha keto acids in BPG shunt Hydroxyethyl PyridoxalphosphatePLP Transamination, decarcoxylation of amino acids Aminogroup Biotin fatty acid synthesis, TCA cycle carbondioxide Co- enzyme-A Co-A TCAcycle, fatty acid synthesis,gluconeogenisis, activation of acetoacetate, detoxification Acylgroup Tetrahydrofolate FH4 Transmethylation reactions where methyl group required for synthesis of choline , epinephrine , creatine. One carbon groups AdenosinetriphosphateATP universal energy currwncy Phosphate 