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The correct answer is e. There is one of two pathways that can be taken, depending on the levels of glucose in the body. If glucose levels are high, the beta-islet cells of the pancreas will secrete insulin which will bind to the liver, causing it to store glucose in the form of glycogen. If glucose levels are low, the alpha-islet cells of the pancreas will secrete glucagon, which will bind to the liver, causing it to break down glycogen and increase the levels of glucose. When insulin receptors cluster due to the binding of insulin, tyrosine kinase is activated, thus causing a cellular response. When the G-protein is activated by glucagon, it releases GTP, which can bind to Adenylate Cyclase and convert ATP into cAMP. cAMP then activates Protein Kinase A, which can phosphorylate other enzymes in the cytoplasm or increase gene expression of glucose in the nucleus.
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