Gluconeogenesis Lecture Notes

These practice flashcards cover the definition, substrates, enzymatic pathways, energy requirements, and hormonal regulation of gluconeogenesis based on the provided lecture notes.

What is the definition of gluconeogenesis?

Gluconeogenesis is the metabolic process by which new glucose is synthesized from non-carbohydrate sources.

Which primary organs perform gluconeogenesis?

Gluconeogenesis occurs mainly in the liver and kidney, and is much less important in the intestinal epithelium.

Where is gluconeogenesis located within the cell?

The process is distributed between the cytosol and the mitochondria.

At what point during fasting does gluconeogenesis become fully active?

It becomes fully active after the depletion of liver glycogen, which typically occurs between $12-18\,\text{hrs}$.

Besides fasting, what other conditions are characterized by active gluconeogenesis?

Diabetes Mellitus, Cushing syndrome, intake of cortisol, severe muscle exercise, and an unbalanced diet.

What role does the Cori cycle play during severe muscle exercise?

The Cori cycle (or Lactic acid cycle) provides lactate from anaerobic glycolysis in exercising skeletal muscles and RBCs as a substrate for gluconeogenesis in the liver.

Why can't glycerol be utilized for gluconeogenesis in adipose tissue?

Adipose tissue lacks the enzyme glycerol kinase.

Which amino acid is considered the major gluconeogenic amino acid?

Alanine.

Which two amino acids are purely ketogenic and cannot participate in gluconeogenesis?

Leucine and lysine.

What are the common sources of Propionyl-CoA used in gluconeogenesis?

It comes from the oxidation of odd-number fatty acids and the catabolism of amino acids valine, isoleucine, methionine, and threonine.

What is the primary function of the Glucose-Alanine Cycle (Cahill Cycle)?

It washes excess ammonia in a non-toxic form and supplies pyruvate as a substrate for gluconeogenesis in the liver.

List the four unique regulatory enzymes of gluconeogenesis.

1. Pyruvate carboxylase, 2. Phosphoenolpyruvate carboxykinase (PEPCK), 3. Fructose 1,6-bisphosphatase, 4. Glucose 6-phosphatase.

What cofactor is required by Pyruvate carboxylase?

Biotin (Vitamin B7).

What is the energy requirement for converting 2 molecules of pyruvate into one molecule of glucose?

The process requires $6\,\text{ATP}$ (comprising $4\,\text{ATP} + 2\,\text{GTP}$) and the oxidation of $2\,\text{NADH}$.

How much energy is required to produce glucose starting from glycerol?

$2\,\text{ATP}$ are required to produce one molecule of glucose from glycerol.

How do glucagon and epinephrine regulate the four key gluconeogenic enzymes?

They stimulate the induction of these four enzymes.

What is the allosteric effect of Acetyl CoA on Pyruvate carboxylase?

Acetyl CoA acts as an allosteric activator ($+\text{activation}$) of Pyruvate carboxylase.

How does Fructose 2,6-bisphosphate influence gluconeogenesis?

A decrease in Fructose 2,6-bisphosphate levels (stimulated by glucagon) leads to the inhibition of PFK-1 and the stimulation of Fructose 1,6-bisphosphatase, thus turning on gluconeogenesis.

What is the importance of gluconeogenesis for the brain and RBCs?

It maintains blood glucose levels to ensure a continuous supply of metabolic fuel for the brain and erythrocytes.

What condition is specifically associated with the deficiency of the enzyme Glucose-6-phosphatase?

Von Gierke Disease.