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

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

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

    What is the significance of biotin in gluconeogenesis?

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

    What is the primary role of PEPCK in gluconeogenesis?

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

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

    <p>PEPCK1</p> Signup and view all the answers

    What condition is primarily associated with PEPCK deficiency?

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

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

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

    How does PEPCK2 contribute to the gluconeogenesis pathway?

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

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

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

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

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

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

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

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

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

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

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

    What is the primary role of glucose 6-phosphatase?

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

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

    <p>FBP1</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</p> Signup and view all the answers

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

    <p>G6PC4</p> Signup and view all the answers

    In which tissue is G6PC1 predominantly expressed?

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

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

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

    What is a primary treatment for G6Pase deficiency?

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

    What are gluconeogenic precursors?

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

    Where does glycerol, a gluconeogenic precursor, originate from?

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

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

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

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

    <p>Causes muscle cramps</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 role of glycogen phosphorylase in glycogen metabolism?

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

    What prevents muscle tissue from synthesizing glucose through gluconeogenesis?

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

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

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

    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

    Description

    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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