WBR0875

Author	[[PageAuthor::Serge Korjian M.D. (Reviewed by Serge Korjian)]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Biochemistry
Sub Category	SubCategory::Endocrine
Prompt	[[Prompt::A researcher is studying the effects of insulin on human muscle cells. After successfully culturing a line of skeletal muscle cells, he applies doses of insulin in small increments and then monitors the effective changes by analyzing samples of cell lysate and samples of the culture broth. He notices that as insulin doses increase the intracellular concentration of glycogen increases while the extracellular concentration of glucose steadily decreases. Which of the following intracellular pathways in responsible for the regulation of both occurrences?]]
Answer A	AnswerA::RAS/MAP kinase pathway
Answer A Explanation	AnswerAExp::The RAS/MAPK pathway is responsible for the effects of insulin on cell growth and DNA synthesis. It is not associated glycogen synthesis.
Answer B	AnswerB::APC/Beta-catenin pathway
Answer B Explanation	AnswerBExp::The APC/Beta-catenin pathway in essential in Wnt signaling and gene regulation. It is not involved in glucose absorption or glycogen synthesis.
Answer C	AnswerC::Adenylate cyclase/PKA pathway
Answer C Explanation	AnswerCExp::The adenylate cyclase/PKA pathway is not associated with insulin signaling.
Answer D	AnswerD::Fas/FADD pathway
Answer D Explanation	AnswerDExp::The Fas/FADD pathway is involved in apoptosis signaling. It is not associated with insulin signaling.
Answer E	AnswerE::PI3k pathway
Answer E Explanation	AnswerEExp::The PI3k pathway is the second messenger pathway involved in increasing glucose uptake and glycogen synthesis after insulin signaling.
Right Answer	RightAnswer::E
Explanation	[[Explanation::Insulin is a peptide hormone, produced by beta cells of the pancreas, and is central to regulating carbohydrate and fat metabolism in the body. Insulin causes cells in the liver, skeletal muscles, and fat tissue to absorb glucose from the blood and produce glycogen (liver and muscle) and triglycerides (adipocytes). Insulin binding to its receptor causes downstream activation of 2 processes: The RAS/MAPK pathway and the PI3k pathway. Both glucose absorption and glycogen synthesis are due to the effects of PI3k pathway activation. PI3K leads to PIP3 formation that activates protein kinase B. PKB phosphorylates glycogen synthase kinase and inactivates it leading to increased activity of glycogen synthase. PKB also facilitates GLUT-4 expression leading to increased glucose uptake. The RAS/MAPK pathway is responsible for the effects of insulin on cell growth and DNA synthesis. Educational Objective: Insulin activates the PI3k pathway that leads to increased glucose absorption and glycogen synthesis. References: White MF, Kahn CR. The insulin signaling system. J Biol Chem. 1994;269(1):1-4.]]
Approved	Approved::Yes
Keyword	WBRKeyword::PI3K pathway, WBRKeyword::Insulin, WBRKeyword::Glycogen, WBRKeyword::Glucose
Linked Question	Linked::
Order in Linked Questions	LinkedOrder::