Insulin Secretion Pathway Quiz
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Insulin Secretion Pathway Quiz

Test your knowledge on the pathway of insulin secretion, starting from glucose phosphorylation by glucokinase to the release of insulin into circulation. Explore how ATP production, membrane depolarization, calcium ion influx, and GLUT-4 vesicle migration are all involved in this intricate process.

Created by
@FatihSultanMehmet

Questions and Answers

What is the main mechanism by which insulin stimulates glucose uptake in adipose and skeletal muscle tissue?

Insulin stimulates the migration of intracellular GLUT-4 vesicles to fuse with the plasma membrane, leading to increased glucose uptake.

What is the role of the enzyme glucokinase in the liver?

Glucokinase is activated by insulin and has a high Vmax, allowing it to quickly convert glucose into glucose-6-phosphate.

What is the role of the ATP-K+ channel in the insulin secretion process?

The closure of the ATP-K+ channel causes membrane depolarization, which leads to the opening of voltage-gated calcium channels.

How does increased glucose phosphorylation by glucokinase lead to increased insulin secretion?

<p>Increased glucose phosphorylation leads to increased glycolysis, which increases ATP levels and closes ATP-K+ channels, causing membrane depolarization and calcium influx.</p> Signup and view all the answers

What is the significance of the high Vmax of glucokinase in the liver?

<p>The high Vmax of glucokinase allows it to quickly convert glucose into glucose-6-phosphate when blood glucose concentrations exceed 180 mg/dL.</p> Signup and view all the answers

How does the presence of insulin and high glucose-6-phosphate concentrations in the cytosol stimulate glycolysis?

<p>Insulin and high glucose-6-phosphate concentrations activate the enzyme glucokinase, leading to increased glucose phosphorylation and glycolysis.</p> Signup and view all the answers

Where does glycogen synthesis mainly occur?

<p>Liver and muscle</p> Signup and view all the answers

What is the function of liver glycogen?

<p>To maintain blood glucose concentration in fasting state</p> Signup and view all the answers

Which enzyme catalyzes the phosphorylation of glucose in muscle?

<p>Hexokinase</p> Signup and view all the answers

What catalyzes the transfer of glucose residues to form a glycogen primer?

<p>Glycogenin</p> Signup and view all the answers

Why does glycogenesis mainly occur in muscle and liver?

<p>Because muscle lacks glucose-6-phosphatase</p> Signup and view all the answers

What occurs to liver glycogen concentrations after 12 to 18 hours of fasting?

<p>They are totally depleted</p> Signup and view all the answers

What is the primary role of the citrate that accumulates in the mitochondrial matrix?

<p>To inhibit the citric acid cycle and promote lipogenesis</p> Signup and view all the answers

Which of the following pathways is initiated when glucose-6-phosphate levels increase in the cytoplasm?

<p>The pentose phosphate pathway and glycogenesis</p> Signup and view all the answers

What is the primary function of the pentose phosphate pathway?

<p>To produce NADPH for fatty acid synthesis and ribose for nucleic acid synthesis</p> Signup and view all the answers

What is the primary function of glycogenesis?

<p>To regulate blood glucose concentration in normoglycemic ranges</p> Signup and view all the answers

What is the primary storage form of carbohydrates in animals?

<p>Glycogen</p> Signup and view all the answers

What is the primary role of pyruvate dehydrogenase (PDH) in the context of glucose metabolism?

<p>To initiate the citric acid cycle</p> Signup and view all the answers

What is the role of glycogen in the liver?

<p>Provide free glucose for export to maintain blood glucose concentration</p> Signup and view all the answers

Which enzyme catalyzes the phosphorylation of glycogen phosphorylase to activate it?

<p>Phosphorylase kinase</p> Signup and view all the answers

What effect does 5' AMP have on glycogen phosphorylase activity?

<p>Activates glycogen phosphorylase</p> Signup and view all the answers

Which hormone leads to the dephosphorylation and activation of glycogen synthase in muscle?

<p>Insulin</p> Signup and view all the answers

What is responsible for the inactivation of glycogen phosphorylase in both liver and muscle?

<p>Glucose-6-phosphate</p> Signup and view all the answers

Which process leads to the formation of glycogen phosphorylase a in response to hormones like epinephrine and glucagon?

<p>Phosphorylation</p> Signup and view all the answers

What is the primary use of muscle glycogen?

<p>Provide glucose-6-phosphate for muscle energy metabolism</p> Signup and view all the answers

What inhibits pyruvate dehydrogenase in muscle?

<p>Fatty acids</p> Signup and view all the answers

Which process involves the transamination of pyruvate to alanine?

<p>Glucose-Alanine cycle</p> Signup and view all the answers

What is the fate of most of the pyruvate transaminated to alanine in muscle?

<p>Exported to other tissues</p> Signup and view all the answers

Why cannot muscle glycogen directly contribute to plasma glucose?

<p>Missing glucose-6-phosphatase</p> Signup and view all the answers

What is the main function of alanine exported from muscle to the liver?

<p>Substrate for gluconeogenesis</p> Signup and view all the answers

Study Notes

Glucose Uptake and Insulin Signaling

  • Increased glucose phosphorylation by glucokinase leads to increased glycolysis, ATP formation, and membrane depolarization, ultimately resulting in insulin secretion.
  • Insulin stimulates the migration of GLUT-4 vesicles to the plasma membrane, increasing glucose uptake in adipose and skeletal muscle tissue.

Hexokinase and Glucokinase

  • Hexokinase has a high affinity for glucose and is saturated under normal conditions, providing glucose-6-phosphate to meet the liver's needs.
  • Glucokinase, on the other hand, has a high Km and is activated when blood glucose concentrations exceed 180 mg/dL, with a high Vmax value.

Glucose Metabolism in the Liver

  • Glucose breakdown to pyruvate and pyruvate enters the mitochondrial matrix.
  • Pyruvate is converted to acetyl-CoA by PDH, which enters the citric acid cycle.
  • When adequate ATP is synthesized, it blocks regulatory enzymes of the citric acid cycle, leading to citrate accumulation in the matrix.
  • Citrate in the matrix leaks into the cytoplasm, initiating lipogenesis and cholesterol biosynthesis.

Regulation of Glycolysis

  • Citrate in the cytoplasm inhibits PFK-1 activity, slowing down glycolysis.
  • High glucose-6-phosphate concentrations in the cytoplasm initiate other metabolic pathways, such as the pentose phosphate pathway and glycogenesis.

Glycogen Metabolism

  • Glycogen is the major storage carbohydrate in animals, corresponding to starch in plants.
  • It is a branched polymer of α-D-glucose and occurs mainly in the liver and muscle.
  • Liver glycogen functions as a reserve to maintain blood glucose concentration in the fasting state.
  • Muscle glycogen provides a readily available source of glucose-1-phosphate for glycolysis within the muscle itself.

Glycogenesis

  • Glycogenesis occurs mainly in the liver and muscle.
  • Glucose is phosphorylated to glucose-6-phosphate, which is then isomerized to glucose-1-phosphate.
  • Glucose-1-phosphate reacts with UTP to form UDP-Glc, which is then used to form a glycogen primer.
  • The glycogenin protein catalyzes the transfer of further glucose residues to form a glycogen primer.

Regulation of Glycogen Synthesis and Breakdown

  • Glycogen phosphorylase is activated by phosphorylation and inactivated by dephosphorylation in response to hormonal and other signals.
  • Glycogen synthase is activated by dephosphorylation and inactivated by phosphorylation in response to hormonal signals.
  • ATP, glucose-6-phosphate, and Ca2+ are negative allosteric effectors of glycogen phosphorylase, while 5' AMP is a positive allosteric effector.
  • Glucose-6-phosphate is a positive allosteric effector of glycogen synthase.

Muscle Glycogen and Glucose-Alanine Cycle

  • Muscle glycogen cannot contribute directly to plasma glucose, since muscle lacks glucose-6-phosphatase.
  • Pyruvate formed by glycolysis in muscle can undergo transamination to alanine, which is exported from muscle and used for gluconeogenesis in the liver.
  • Acetyl-CoA formed by oxidation of fatty acids in muscle inhibits pyruvate dehydrogenase, leading to an accumulation of pyruvate, which is then transaminated to alanine.

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