Gluconeogenesis and Glycolysis Quiz
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Questions and Answers

What is the main function of gluconeogenesis?

  • Synthesize glucose from non-carbohydrate substrates (correct)
  • Metabolize lactate into pyruvate
  • Break down fatty acids for energy
  • Convert glucose to glycogen

Which organs are primarily responsible for gluconeogenesis?

  • Spleen and pancreas
  • Heart and lungs
  • Brain and muscle
  • Liver and kidneys (correct)

What role does acetyl CoA play in the regulation of pyruvate carboxylase?

  • It allosterically activates the enzyme (correct)
  • It deactivates the enzyme in the presence of high concentrations
  • It serves as a substrate for the enzyme
  • It is produced as a byproduct of the reaction

What is the first step in the gluconeogenesis process involving pyruvate?

<p>Carboxylation of pyruvate (A)</p> Signup and view all the answers

Why must oxaloacetate be converted to malate before transport to the cytosol?

<p>Oxaloacetate cannot cross the inner mitochondrial membrane directly (C)</p> Signup and view all the answers

What happens at low levels of acetyl CoA in relation to pyruvate?

<p>Pyruvate undergoes the TCA cycle (D)</p> Signup and view all the answers

Which of the following enzymes is responsible for the conversion of oxaloacetate to phosphoenolpyruvate?

<p>PEP carboxykinase (D)</p> Signup and view all the answers

What is the significance of biotin in gluconeogenesis?

<p>It is a coenzyme for pyruvate carboxylase (A)</p> Signup and view all the answers

What is the primary role of PEPCK in gluconeogenesis?

<p>Converts phosphoenolpyruvate to oxaloacetate (D)</p> Signup and view all the answers

Which PEPCK isoform is predominantly regulated by mitochondrial GTP-dependent pathways?

<p>PEPCK1 (C)</p> Signup and view all the answers

What condition is primarily associated with PEPCK deficiency?

<p>Lactic acidosis (B)</p> Signup and view all the answers

What is a consequence of the inhibition of gluconeogenesis due to PEPCK enzyme deficiency?

<p>Reye syndrome (A)</p> Signup and view all the answers

How does PEPCK2 contribute to the gluconeogenesis pathway?

<p>By generating NADH from pyruvate (C)</p> Signup and view all the answers

What treatment is recommended for managing acute episodes of PEPCK deficiency?

<p>Glucose and bicarbonate infusions (C)</p> Signup and view all the answers

Which of the following symptoms is NOT associated with PEPCK deficiency?

<p>Hypertension (C)</p> Signup and view all the answers

Which reaction does fructose 1, 6-bisphosphatase catalyze in gluconeogenesis?

<p>Hydrolysis of fructose 1, 6-bisphosphate (C)</p> Signup and view all the answers

What inhibits fructose-1,6-bisphosphatase in an energy poor state?

<p>Adenosine monophosphate (C)</p> Signup and view all the answers

Which enzyme catalyzes the reversible production of fructose-1,6-bisphosphate from fructose-6-phosphate?

<p>Fructose-1,6-bisphosphatase (C)</p> Signup and view all the answers

Fructose-1,6-bisphosphatase deficiency would primarily lead to which clinical symptoms?

<p>Hyperventilation and hypoglycemia (B)</p> Signup and view all the answers

Which method is commonly used for diagnosing fructose-1,6-bisphosphatase enzyme deficiency?

<p>Spectrophotometric and load tests (A)</p> Signup and view all the answers

What is the primary role of glucose 6-phosphatase?

<p>Hydrolyze glucose 6-phosphate (B)</p> Signup and view all the answers

What compounds are typically avoided in the treatment of hypoglycemia for patients with FBPase deficiency?

<p>Sucrose and fructose (D)</p> Signup and view all the answers

Which of the following is a characteristic feature of fructose-1,6-bisphosphatase?

<p>It consists of four identical subunits (C)</p> Signup and view all the answers

FBPase is encoded by which gene in the liver and kidney?

<p>FBP1 (C)</p> Signup and view all the answers

What is the primary function of glucose-6-phosphatase (G6Pase)?

<p>To convert glucose-6-phosphate to glucose (C)</p> Signup and view all the answers

Which of the following genes is NOT associated with glucose-6-phosphatase?

<p>G6PC4 (A)</p> Signup and view all the answers

In which tissue is G6PC1 predominantly expressed?

<p>Liver (D)</p> Signup and view all the answers

What are the long-term complications associated with glycogen storage disease type 1a (GSD-1a)?

<p>Pulmonary hypertension and osteopenia (B)</p> Signup and view all the answers

What is a distinguishing symptom of GSD-1b that differentiates it from GSD-1a?

<p>Neutropenia (C)</p> Signup and view all the answers

Which condition is characterized by excessive accumulation of glycogen in the liver, kidney, and intestinal mucosa?

<p>Glycogen storage disease type 1 (C)</p> Signup and view all the answers

What is a common clinical sign noticed around 3 months of age in GSD-1a patients?

<p>Protruded abdomen due to hepatomegaly (A)</p> Signup and view all the answers

Which statement is true regarding the function of SLC37A4 encoded gene?

<p>It transports glucose-6-phosphate to the endoplasmic reticulum (A)</p> Signup and view all the answers

What is one of the main diagnostic indicators for Crohn’s disease in GSD-1b patients?

<p>Presence of anti-CBir1 antibodies (C)</p> Signup and view all the answers

Which of the following conditions is more common in GSD-1b patients compared to GSD-1a patients?

<p>Splenomegaly (B)</p> Signup and view all the answers

What is the role of granulocyte colony-stimulating factor (G-CSF) in GSD-1b patients?

<p>Improves the function of circulating neutrophils (B)</p> Signup and view all the answers

What is a primary treatment for G6Pase deficiency?

<p>Corn starch and carbohydrates (A)</p> Signup and view all the answers

Which type of transplantation is an option for patients with GSD-1a if dietary therapy is ineffective?

<p>Liver transplantation (C)</p> Signup and view all the answers

What are gluconeogenic precursors?

<p>Molecules that can contribute to glucose synthesis (D)</p> Signup and view all the answers

Where does glycerol, a gluconeogenic precursor, originate from?

<p>Hydrolysis of triacylglycerol in adipose tissue (D)</p> Signup and view all the answers

Which of the following substances is NOT classified as a gluconeogenic precursor?

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

What is the primary reason that ketogenic compounds cannot contribute to gluconeogenesis?

<p>They are transformed into ketone bodies instead. (D)</p> Signup and view all the answers

Which process allows lactate produced in muscle during exercise to be converted back into glucose?

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

Which function is NOT provided by gluconeogenesis during periods of low carbohydrate availability?

<p>Synthesis of fatty acids (B)</p> Signup and view all the answers

What is the effect of lactate accumulation in muscle tissues during intense exercise?

<p>Causes muscle cramps (A)</p> Signup and view all the answers

What is the primary storage form of carbohydrates in animals?

<p>Glycogen (B)</p> Signup and view all the answers

What is the role of glycogen phosphorylase in glycogen metabolism?

<p>It cleaves α-1, 4 glycosidic bonds during glycogenolysis. (B)</p> Signup and view all the answers

What prevents muscle tissue from synthesizing glucose through gluconeogenesis?

<p>Lack of glucose 6 phosphatase (D)</p> Signup and view all the answers

During glycogenolysis, what remains on the glycogen chain before a branch point?

<p>Four glucose units (B)</p> Signup and view all the answers

Flashcards

Gluconeogenesis

The creation of new glucose from non-carbohydrate sources.

Gluconeogenesis Precursors

Lactate, pyruvate, glycerol, and keto acids are the starting materials for gluconeogenesis.

Liver's role in Gluconeogenesis

Liver produces about 90% of new glucose molecules in gluconeogenesis.

Kidney's role in Gluconeogenesis

Kidneys make about 10% of glucose molecules during gluconeogenesis, becoming more crucial during prolonged fasting.

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Pyruvate Carboxylase

Enzyme that carboxylates pyruvate to oxaloacetate in mitochondria.

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Acetyl CoA activation

Elevated levels of Acetyl CoA stimulate pyruvate carboxylase, favoring glucose synthesis.

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Oxaloacetate Transport

Oxaloacetate is converted to malate for transport out of mitochondria and back to oxaloacetate in the cytosol.

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PEP Carboxykinase

Enzyme converting oxaloacetate to phosphoenolpyruvate (PEP) in cytosol.

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PEPCK Deficiency

An autosomal recessive disorder affecting gluconeogenesis, characterized by lactic acidosis and hypoglycemia.

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PEPCK enzyme

Enzyme crucial in gluconeogenesis, converting pyruvate to phosphoenolpyruvate (PEP).

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Fructose 1, 6-bisphosphatase

Enzyme catalyzing the hydrolysis of fructose 1, 6-bisphosphate to fructose 6-phosphate, driving gluconeogenesis forward in a favorable way.

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Lactic acidosis

Condition characterized by an excessive buildup of lactic acid in the bloodstream, a common symptom of PEPCK deficiency.

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Hypoglycemia

Low blood sugar level, a key symptom of PEPCK deficiency.

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Pyruvate carboxylase and PEP carboxykinase

Two enzymes working together to efficiently convert pyruvate into PEP for gluconeogenesis.

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Gluconeogenesis pathway

The series of reactions converting non-carbohydrate molecules into glucose, crucial for maintaining blood sugar levels.

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Fructose-1,6-bisphosphatase inhibition

Elevated AMP levels inhibit Fructose-1,6-bisphosphatase, signaling low cellular energy.

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FBPase activation

High ATP and low AMP levels stimulate gluconeogenesis by activating Fructose-1,6-bisphosphatase.

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FBPase Deficiency

A metabolic disorder where the enzyme Fructose-1,6-bisphosphatase is deficient, causing life-threatening symptoms.

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Gluconeogenesis regulation

The process of synthesizing glucose from non-carbohydrate sources, regulated by energy levels (ATP,AMP) in the cell.

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FBPase function

The enzyme Fructose-1,6-bisphosphatase catalyzes the reversible production of fructose-1,6-bisphosphate.

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Glucose 6-phosphatase location

This enzyme is found in liver and kidney, but not in muscle.

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Glucose 6-phosphatase bypass

Hydrolyzing glucose 6-phosphate using glucose 6-phosphatase creates a favorable route to produce free glucose.

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Diagnosis of FBPase Deficiency

Diagnosis of deficiency can be achieved through various methods, including spectrophotometric tests, radiochemical load tests in specific tissues (liver, kidney, jejunum).

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G6Pase

An enzyme essential for glucose production, located in the lumen of the endoplasmic reticulum (ER). It converts glucose-6-phosphate to glucose.

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GSD type 1a

A type of glycogen storage disease caused by a deficiency in G6Pase, resulting in hypoglycemia, hyperlactacidemia, and hepatomegaly.

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GSD type 1b

A type of glycogen storage disease caused by a deficiency in the glucose-6-phosphatase translocase (G6PT), leading to similar symptoms as GSD1a with the addition of neutropenia.

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G6PC1

A gene responsible for G6Pase production, expressed primarily in the liver, kidney, and small intestine. Mutations in this gene cause GSD type 1a.

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G6PC2

A gene responsible for G6Pase production, expressed predominantly in the pancreas. Mutations in this gene can lead to rare metabolic disorders.

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G6PC3

A gene responsible for G6Pase production, ubiquitously expressed throughout the body.

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SLC37A4

A gene encoding a transporter protein that moves glucose-6- phosphate from the cytosol into the ER, where G6Pase acts.

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GSD-1b Diagnosis

The presence of anti-CBir1 antibodies and elevated granulocyte colony-stimulating factor (GCSF) levels can indicate GSD-1b.

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GSD-1b Symptoms

GSD-1b patients often experience splenomegaly and hepatomegaly, unlike GSD-1a patients.

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G6Pase Deficiency Treatment

Corn starch and other carbohydrates are the primary treatment for G6Pase deficiency.

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G6Pase Deficiency Adjunct Therapy

Allopurinol, ACE inhibitors, lipid-lowering drugs, and potassium citrate are used as supplementary treatments for G6Pase deficiency.

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GSD-1a Treatment

Liver transplantation can be considered for unresponsive GSD-1a patients with hepatocellular adenoma or tumors.

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GSD-1b Treatment

Bone marrow transplantation may be an option for GSD-1b patients with myeloid deficiencies.

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Glycerol as a Precursor

Released during fat breakdown, glycerol is converted to glycerophosphate, a glycolysis intermediate.

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Ketogenic Compounds

Compounds that can't be used to directly synthesize glucose due to the irreversible nature of the pyruvate dehydrogenase reaction. They contribute to ketone body formation.

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Pyruvate Dehydrogenase Reaction

The irreversible reaction that converts pyruvate into acetyl CoA.

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Gluconeogenesis Advantage: Glucose Availability

Gluconeogenesis provides glucose when dietary carbohydrates are insufficient.

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Gluconeogenesis Advantage: Blood Glucose Regulation

Gluconeogenesis helps maintain stable blood glucose levels.

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Gluconeogenesis Advantage: Energy for Tissues

Gluconeogenesis supplies glucose to tissues like the brain and red blood cells that primarily rely on glucose for energy.

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Cori Cycle

A metabolic cycle where lactate produced in muscles during exercise is transported to the liver and converted back to glucose.

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Muscle's Limitation in Gluconeogenesis

Muscle lacks the enzyme glucose 6-phosphatase, preventing it from releasing glucose into the bloodstream.

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Glycogen Phosphorylase

Enzyme that breaks down glycogen by cleaving α-1, 4 glycosidic bonds, releasing glucose units.

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Study Notes

Gluconeogenesis

  • Gluconeogenesis is the synthesis of new glucose from non-carbohydrate substrates
  • In the absence of dietary carbohydrates, liver glycogen can provide glucose for only 10-18 hours
  • During prolonged fasting, liver glycogen stores deplete, and glucose is synthesized from precursors like lactate, pyruvate, glycerol, and keto acids
  • Approximately 90% of gluconeogenesis occurs in the liver, with kidneys contributing 10%
  • The kidneys' role is minor except during prolonged starvation, when they become major glucose producers

Glycolysis and Gluconeogenesis

  • The diagram shows the interconnected pathways of glycolysis and gluconeogenesis.
  • Glycolysis converts glucose to pyruvate
  • Gluconeogenesis converts pyruvate back to glucose
  • Both pathways share many reversible reactions, but there are three irreversible reactions bypassed in gluconeogenesis by different enzymes (e.g. pyruvate carboxylase, PEPCK)

Reactions Unique to Gluconeogenesis

  • Pyruvate is carboxylated to oxaloacetate by pyruvate carboxylase.
  • Oxaloacetate is converted to phosphoenolpyruvate (PEP) by PEP carboxykinase.
  • These reactions bypass irreversible steps in glycolysis, requiring energy, often in the form of GTP hydrolysis.

Allosteric Regulation of Pyruvate Carboxylase

  • Pyruvate carboxylase is allosterically activated by acetyl CoA.
  • Elevated acetyl CoA levels indicate energy needs, stimulating OAA production for gluconeogenesis.
  • At low levels of acetyl CoA, pyruvate carboxylase is inactive and pyruvate is mainly oxidized in the TCA cycle

Transport of Oxaloacetate to the Cytosol

  • Oxaloacetate formed in the mitochondria must be transported to the cytosol for gluconeogenesis.
  • It is reduced to malate, which can cross the mitochondrial membrane.
  • Malate is then reoxidized to oxaloacetate in the cytosol

Decarboxylation of Cytosolic Oxaloacetate

  • In the cytosol, oxaloacetate is decarboxylated and phosphorylated to PEP by PEPCK.
  • This reaction is driven by GTP hydrolysis.

Phosphoenolpyruvate Carboxykinase (PEPCK) Deficiency

  • PEPCK is essential for gluconeogenesis, converting PEP to oxaloacetate.
  • There are isoforms of PEPCK (PEPCK1 and PEPCK2).
  • PEPCK1 is regulated by mitochondrial GTP-dependent pathways and hormones, playing a role in glyceroneogenesis in the liver and adipose tissue.
  • PEPCK2 is related to gluconeogenesis, converting pyruvate to oxaloacetic acid and providing cytosolic NADH from lactic acid
  • Deficiency leads to hypoglycemia and lactic acidosis.

C- Dephosphorylation of Fructose 1,6 Bisphosphate

  • Hydrolysis of fructose 1,6-bisphosphate by fructose 1,6-bisphosphatase bypasses the irreversible PFK-1 reaction.
  • This provides a favorable reaction for fructose-6-phosphate production
  • Fructose-1,6-bisphosphatase regulation depends on AMP/ATP cellular energy levels

Fructose-1,6-bisphosphatase (FBPase) Deficiency

  • FBPase is a key enzyme in gluconeogenesis.
  • Deficiency results in hyperventilation, hypoglycemia, and lactic acidosis, and ketosis.
  • Diagnosis involves biochemical tests (spectrophotometric load tests in various tissues).

Glucose 6-phosphatase (G6Pase) Deficiency

  • G6Pase is critical for glucose production from glucose-6-phosphate.
  • Deficiency results in glycogen storage disorder type 1 (GSD type 1), manifesting with severe hypoglycemia, lactic acidosis, and other symptoms.
  • G6Pase activity is located in the liver, kidneys, and small intestine.
  • Testing involves gene expression tests and DNA analysis.

Glycogen Metabolism

  • Glycogen is a major carbohydrate storage form in animals.
  • Stored primarily in liver and muscles.
  • Key enzyme in glycogenolysis is glycogen phosphorylase, which breaks down glycogen by simple phosphorolysis, releasing glucose-1-phosphate.
  • This is converted to glucose-6-phosphate by phosphoglucomutase.
  • In liver and kidneys, glucose-6-phosphate is hydrolyzed to glucose by glucose-6-phosphatase.
  • Skeletal muscle lacks glucose-6-phosphatase and thus cannot release glucose into the blood.
  • Debranching enzyme (glucantransferase) removes branches in glycogen.

Substrates for Gluconeogenesis

  • Substrates include intermediates of glycolysis and the citric acid cycle.
  • Key substrates are glycerol (from triacylglycerol hydrolysis), lactate, and glucogenic amino acid α-keto acid precursors.

Advantages of Gluconeogenesis

  • Maintaining blood glucose levels when carbohydrate intake is insufficient.
  • Providing a source of energy for the nervous system and erythrocytes.
  • Maintaining the intermediates of the TCA cycle.
  • Clearing the products of metabolism, such as lactic acid.

Cori Cycle (Lactic Acid Cycle)

  • Lactate produced by anaerobic metabolism in muscle is transported to the liver.
  • In the liver, lactate is converted back to glucose via gluconeogenesis.
  • This cycle efficiently reuses lactate and maintains blood glucose homeostasis.

Glycogen Storage Diseases (GSDs)

  • GSDs are genetic disorders affecting glycogen metabolism.
  • Deficiency in an enzyme involved in glycogen synthesis or degradation.
  • Manifestations vary according to the specific enzyme deficiency.
  • Examples include Von Gierke's disease (GSD type 1), Pompe's disease (GSD type II), and McArdle's disease (GSD type V).

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Gluconeogenesis PDF

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Test your knowledge on gluconeogenesis and its connection to glycolysis. This quiz covers key concepts, unique reactions, and the role of the liver and kidneys in glucose synthesis. Ideal for students studying biochemistry or metabolism.

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