Biochemistry: Glucose Transport and Metabolism
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Questions and Answers

What condition is associated with mutations in the GLUT2 gene?

  • Maturity Onset Diabetes of the Young
  • Type I diabetes
  • Hypoglycemic Shock
  • Fanconi-Bickel Syndrome (correct)
  • What primarily triggers the translocation of GLUT4 to the plasma membrane?

  • Exercise-induced signaling
  • Low oxygen levels
  • Insulin binding to its receptor (correct)
  • Increased glucose concentration
  • What is the role of GLUT4 in the body?

  • To transport fatty acids
  • To regulate cholesterol levels
  • To mediate protein synthesis
  • To facilitate insulin-mediated glucose uptake (correct)
  • What effect does inhibition of GLUT4 have on insulin sensitivity?

    <p>Causes acute peripheral insulin resistance</p> Signup and view all the answers

    Which of the following cell types does NOT prominently express GLUT4?

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

    What is the initial substrate for the synthesis of cortisol?

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

    In which cellular organelle does the conversion of pregnenolone to progesterone occur?

    <p>Endoplasmic reticulum</p> Signup and view all the answers

    What role does cortisol play in gluconeogenesis?

    <p>It activates transcription of the PEPCK gene.</p> Signup and view all the answers

    What is the final product produced from 11-deoxycortisol in the mitochondria?

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

    Which cycle describes the conversion of lactate formed by skeletal muscle into glucose in the liver?

    <p>Cori Cycle</p> Signup and view all the answers

    What regulates glycolysis and gluconeogenesis allosterically?

    <p>Fructose-2,6-bisphosphate</p> Signup and view all the answers

    Which glucose transporter is sensitive to insulin?

    <p>GLUT4</p> Signup and view all the answers

    Where are high-capacity, bidirectional glucose transporters predominantly expressed?

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

    What is the only regulatory step in the pentose phosphate pathway?

    <p>Oxidation of glucose-6-phosphate</p> Signup and view all the answers

    Which of the following is a genetic deficiency that leads to hemolytic anemia?

    <p>G6PD deficiency</p> Signup and view all the answers

    What differentiates galactosemia from lactose intolerance?

    <p>Galactosemia results from a deficiency in galactose-1-phosphate uridylyltransferase</p> Signup and view all the answers

    Which genetic deficiency is associated with hypoglycemia in premature infants?

    <p>Glycogen storage disease type I</p> Signup and view all the answers

    What is the normal fasting glucose level range for healthy adults?

    <p>80-100 mg/dl</p> Signup and view all the answers

    Which HbA1c level indicates poor glycemic control?

    <p>6.5% and above</p> Signup and view all the answers

    What is the post-prandial glucose level range indicating diabetes?

    <p>140-200 mg/dl</p> Signup and view all the answers

    Study Notes

    Fanconi-Bickel Syndrome

    • Caused by mutations in the GLUT2 gene, resulting in a rare autosomal-recessive disorder.
    • Resembles type I glycogen storage disease.

    GLUT4 Transporter

    • Primarily found in adipocytes, skeletal muscle, and cardiomyocytes.
    • Functions as an insulin-responsive glucose transporter, crucial for glucose homeostasis.
    • Inhibition leads to acute peripheral insulin resistance.
    • Responds to insulin binding through exocytosis, facilitating glucose uptake by mobilizing transporters to the plasma membrane.

    Cortisol and Gluconeogenesis

    • Cortisol synthesized in mitochondria from cholesterol via pregnenolone and subsequent conversions.
    • Plays a role in increasing gluconeogenesis by activating PEPCK (P-EnolPyruvate Carboxykinase) upon binding to glucocorticoid-responsive genes.
    • Essential for elevating hepatic glucose production.

    Cori Cycle

    • Lactate produced by contracting skeletal muscles during intense exercise is converted back to glucose in the liver.
    • Liver returns glucose to muscles for glycolytic breakdown, supporting ATP production.

    Glycemia Values

    • Fast and post-prandial glucose levels categorize states of hypoglycemia, normal glycemia, pre-diabetes, and diabetes.
    • Normal fasting glucose: 80-100 mg/dl, post-prandial glucose < 140 mg/dl.
    • Diabetes characterized by fasting glucose > 126 mg/dl and post-prandial glucose > 200 mg/dl.

    Hemoglobin A1c (HbA1c)

    • Used to diagnose and monitor diabetes, reflecting average blood glucose levels over time.
    • Normal range is 4.4-5.6%; higher levels indicate poorer glycemic control due to non-enzymatic glycation.

    Overview of Glucose Metabolism

    • Includes pathways like glycogenolysis and glycogenesis, glycolysis, and gluconeogenesis.
    • Key enzymatic actions occur in specific tissues, especially liver and kidneys for gluconeogenesis.

    Gluconeogenesis

    • Converts pyruvate to glucose primarily in the liver and renal cortex.
    • Essential for maintaining blood glucose levels, particularly for tissues with low gluconeogenic activity (brain, skeletal muscle, heart).

    Glucose-6-Phosphatase and Wernicke-Korsakoff Syndrome

    • Certain glycolytic reactions contribute to gluconeogenesis.
    • Wernicke-Korsakoff syndrome linked to vitamin B1 deficiency and poor transketolase affinity, affecting carbohydrate metabolism.

    Pentose Phosphate Pathway and Drug Hemolytic Anemia

    • Source of NADPH in erythrocytes, vital for regenerating glutathione from its oxidized form (GSSG).
    • Ratio of GSH to GSSG typically ranges from 100-1000 in normal cells.
    • Glutathione reductase catalyzes reduction of GSSG to GSH using NADPH.

    Glutathione's Role

    • GSH helps detoxify hydrogen peroxide in erythrocytes, with glutathione peroxidase required for this reaction, dependent on selenium as a cofactor.

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    Description

    Explore the details of glucose transport mechanisms, including the roles of GLUT2 and GLUT4 transporters, and their implications in conditions like Fanconi-Bickel Syndrome. Understand the influence of cortisol on gluconeogenesis and the function of the Cori cycle in muscle metabolism. This quiz covers essential concepts in biochemistry related to glucose homeostasis.

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