Endocrine System MCAT Practice Question
A 34-year-old man with no significant medical history undergoes routine fasting labs. His fasting glucose is 95 mg/dL and fasting insulin is 8 mIU/L. Two hours after consuming a 75-gram oral glucose load, his glucose rises to 156 mg/dL. At this timepoint, his pancreatic beta cells have increased their cytoplasmic ATP/ADP ratio, leading to closure of ATP-sensitive potassium channels, membrane depolarization, and opening of voltage-gated calcium channels. The resulting elevation in intracellular calcium concentration triggers a series of molecular events that allow the pancreas to respond appropriately to the glucose stimulus. Which of the following best describes the primary mechanism by which increased intracellular calcium mediates insulin secretion in response to this glucose load?
Answer choices
- AActivation of calmodulin-dependent protein kinase, which phosphorylates and inactivates glycogen synthase to prevent glucose storage
- BBinding of calcium to calmodulin, which activates SNARE proteins required for fusion of insulin-containing vesicles with the plasma membraneCorrect answer
- CActivation of phospholipase C, leading to increased production of diacylglycerol and subsequent activation of protein kinase C
- DDirect calcium-mediated activation of adenylyl cyclase, increasing cAMP levels and enhancing beta cell glucose metabolism
- ECalcium-dependent upregulation of GLUT2 transporters on the beta cell membrane to increase glucose uptake and metabolism
- FBinding of calcium to troponin, causing conformational changes that enhance insulin gene transcription through histone acetylation
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