Glucagon, a peptide hormone, is upregulated when blood sugar levels are low. which molecules in or on the plasma membrane would enable a cell to respond to glucagon and initiate its effects?

Answer;

D. receptor proteins

Explanation;

-Hormones bind with receptors to initiate the cellular response to a chemical signal. Target cells convert the signal into a biochemical change inside the cell. This is done via second messenger systems and also via direct gene activation.

-Receptors are complex proteins that only respond to specific hormones. Receptors for water-soluble hormones are found on the plasma membrane while receptors for lipid-soluble hormones are found in the cytoplasm or the nucleus. Receptors will down-regulate and decrease sensitivity when there is prolonged exposure to high levels of a hormone and also they have the ability to up-regulate and increase sensitivity in response to sustained low levels of a hormone.

A glucagon receptor is present on the plasma membrane of a cell to which the glucagon molecules bind and control the blood glucose level.

Further Explanation:

The secretion of glucagon occurs through the alpha cells present in the islets of Langerhans in the pancreas. It has an important role in regulating the homeostasis of glucose in the body. Therefore, in contrast to insulin which lowers the glucose concentration in blood, glucagon increases the glucose levels by various pathways.

Glucagon is a peptide hormone containing 29 amino acids and is derived from a precursor molecule of proglucagon. The enzymes involved in the formation of glucagon from proglucagon are prohormone convertase 1/3 (PC1/3) in the brain and intestine and PC 2 in the pancreas.

Glucagon is secreted in response to hypoglycemia and its effect is mediated through its binding to the glucagon receptor which is mostly expressed in the liver but sometimes found in the heart, kidney, pancreas, and adrenal glands. This receptor is a G-protein coupled receptor that traverses the membrane seven times. As glucagon binds to its receptor, the receptor gets activated and further stimulates adenylyl cyclase. Cyclic adenosine monophosphate (cAMP) is produced through adenylyl cyclase which activates protein kinase A (PKA). The PKA moves into the nucleus and stimulates CREB (cAMP response element-binding protein). On phosphorylation, CREB binds to the target gene at the response element site and enables gene expression which results in the increased production of glucose through glycogenolysis, gluconeogenesis, or glycolysis.

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Answer Details:

Grade: College Biology

Chapter: Glucagon Physiology

Subject: Biology

Keywords:

Glucagon, a peptide hormone, blood glucose level, pancreas, islets of Langerhans, alpha cells, glucagon receptor, adenylyl cyclase, cAMP, PKA, CREB, glycogenolysis, gluconeogenesis, glycolysis.

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