This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Lipids, Subject name: Biochemistry
Choose the one best answer that most accurately describes some properties of acetyl-CoA carboxylase. 
Select and explain. 
A. Required Cofactor - Biotin; Intracellular Location - Mitochondrial; Allosteric Modifier - Citrate; Enzyme That Catalyzes a Covalent Modification - PKA, B. Required Cofactor - Biotin; Intracellular Location - Cytoplasmic; Allosteric Modifier - Citrate; Enzyme That Catalyzes a Covalent Modification - AMP-activated protein kinase, C. Required Cofactor - Thiamin; Intracellular Location - Mitochondrial; Allosteric Modifier - Acetyl-CoA; Enzyme That Catalyzes a Covalent Modification - PKA, D. Required Cofactor - Thiamin; Intracellular Location - Cytoplasmic; Allosteric Modifier - Acetyl-CoA; Enzyme That Catalyzes a Covalent Modification - AMP-activated protein kinase
B: Required Cofactor - Biotin; Intracellular Location - Cytoplasmic; Allosteric Modifier - Citrate; Enzyme That Catalyzes a Covalent Modification - AMP-activated protein kinase
Answer: B: Required Cofactor - Biotin; Intracellular Location - Cytoplasmic; Allosteric Modifier - Citrate; Enzyme That Catalyzes a Covalent Modification - AMP-activated protein kinase 
Explanation: Biotin is required for the acetyl-CoA carboxylase reaction in which the substrate, acetyl-CoA, is carboxylated by the addition of CO2 to form malonyl-CoA. This reaction occurs in the cytosol. Malonyl-CoA provides the C-2 units that add to the growing fatty acid chain on the fatty acid synthase complex. As the growing chain is elongated, malonyl-CoA is decarboxylated. Citrate is an allosteric activator of the enzyme, and the enzyme is inhibited by phosphorylation by the AMP-activated protein kinase.