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?

Causes acute peripheral insulin resistance (C) Signup and view all the answers

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

Liver cells (B) Signup and view all the answers

What is the initial substrate for the synthesis of cortisol?

Cholesterol (A) Signup and view all the answers

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

Endoplasmic reticulum (D) Signup and view all the answers

What role does cortisol play in gluconeogenesis?

It activates transcription of the PEPCK gene. (C) Signup and view all the answers

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

Cortisol (D) Signup and view all the answers

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

Cori Cycle (A) Signup and view all the answers

What regulates glycolysis and gluconeogenesis allosterically?

Fructose-2,6-bisphosphate (B) Signup and view all the answers

Which glucose transporter is sensitive to insulin?

GLUT4 (C) Signup and view all the answers

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

Liver (D) Signup and view all the answers

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

Oxidation of glucose-6-phosphate (B) Signup and view all the answers

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

G6PD deficiency (D) Signup and view all the answers

What differentiates galactosemia from lactose intolerance?

Galactosemia results from a deficiency in galactose-1-phosphate uridylyltransferase (D) Signup and view all the answers

Which genetic deficiency is associated with hypoglycemia in premature infants?

Glycogen storage disease type I (A) Signup and view all the answers

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

80-100 mg/dl (D) Signup and view all the answers

Which HbA1c level indicates poor glycemic control?

6.5% and above (A) Signup and view all the answers

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

140-200 mg/dl (C) 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.