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Questions and Answers
What two molecules, besides ATP, are required to activate propionic acid?
What two molecules, besides ATP, are required to activate propionic acid?
CoA-SH and acyl-CoA synthase
What is the metabolic product of propionic acid in humans?
What is the metabolic product of propionic acid in humans?
propionyl-CoA
Name two key enzymes in gluconeogenesis that are regulated by hormones.
Name two key enzymes in gluconeogenesis that are regulated by hormones.
Pyruvate carboxylase and phosphoenol pyruvate carboxykinase
How does fructose 2-6 bisphosphate affect phosphofructokinase (PFK) and fructose 1-6 bisphosphatase (F-1,6-BPase)?
How does fructose 2-6 bisphosphate affect phosphofructokinase (PFK) and fructose 1-6 bisphosphatase (F-1,6-BPase)?
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Which two enzymes are influenced by insulin to increase their expression via gene expression?
Which two enzymes are influenced by insulin to increase their expression via gene expression?
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What is the primary location in the body where gluconeogenesis occurs?
What is the primary location in the body where gluconeogenesis occurs?
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Besides pyruvate, name two other major precursors for gluconeogenesis.
Besides pyruvate, name two other major precursors for gluconeogenesis.
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Under what conditions or physiological states is gluconeogenesis especially important?
Under what conditions or physiological states is gluconeogenesis especially important?
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What process generates lactate that is used as a precursor in the Cori cycle?
What process generates lactate that is used as a precursor in the Cori cycle?
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From what molecule is glycerol derived that serves as a precursor for gluconeogenesis?
From what molecule is glycerol derived that serves as a precursor for gluconeogenesis?
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What is the fate of amino acids during fasting or a low-carb diet in relation to gluconeogenesis?
What is the fate of amino acids during fasting or a low-carb diet in relation to gluconeogenesis?
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Name one situation where propionyl CoA is used as a precursor in gluconeogenesis.
Name one situation where propionyl CoA is used as a precursor in gluconeogenesis.
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What are three enzymatic bypass reactions of glycolysis that differ in gluconeogenesis?
What are three enzymatic bypass reactions of glycolysis that differ in gluconeogenesis?
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What two enzymes are required to convert pyruvate to phosphoenolpyruvate (PEP) in the cytosol?
What two enzymes are required to convert pyruvate to phosphoenolpyruvate (PEP) in the cytosol?
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What is the purpose of cytosolic malate dehydrogenase in the conversion of pyruvate to PEP in the cytosol?
What is the purpose of cytosolic malate dehydrogenase in the conversion of pyruvate to PEP in the cytosol?
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Besides the cytosolic pathway, what other pathway can convert oxaloacetate to PEP?
Besides the cytosolic pathway, what other pathway can convert oxaloacetate to PEP?
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In the diagram of Pyruvate to PEP, what other molecule is produced besides PEP, in the conversion of oxaloacetate to PEP using cytosolic and mitochondrial pathways?
In the diagram of Pyruvate to PEP, what other molecule is produced besides PEP, in the conversion of oxaloacetate to PEP using cytosolic and mitochondrial pathways?
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Besides conversion to PEP, what other fate is there for pyruvate?
Besides conversion to PEP, what other fate is there for pyruvate?
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What cofactor is required in the conversion of pyruvate to oxaloacetate?
What cofactor is required in the conversion of pyruvate to oxaloacetate?
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What two molecules are oxaloacetate converted to, in order to transport it out of the mitochondria?
What two molecules are oxaloacetate converted to, in order to transport it out of the mitochondria?
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What reduces oxaloacetate to malate?
What reduces oxaloacetate to malate?
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What is the enzyme that catalyzes the conversion of citrate to OAA in the cytosol?
What is the enzyme that catalyzes the conversion of citrate to OAA in the cytosol?
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Name any two enzymes that are used in gluconeogenesis.
Name any two enzymes that are used in gluconeogenesis.
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What is the activated form of glycerol that is a substrate for glycerol phosphate dehydrogenase?
What is the activated form of glycerol that is a substrate for glycerol phosphate dehydrogenase?
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Which two tissues are the primary sites where glucose is released into the blood?
Which two tissues are the primary sites where glucose is released into the blood?
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What molecule inhibits fructose-1,6-bisphosphatase allosterically?
What molecule inhibits fructose-1,6-bisphosphatase allosterically?
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Besides using glucose, what other molecule can enter gluconeogenesis after conversion to succinyl-CoA?
Besides using glucose, what other molecule can enter gluconeogenesis after conversion to succinyl-CoA?
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What is the product of fructose-1,6-bisphosphatase, specifically in the pathway of gluconeogenesis?
What is the product of fructose-1,6-bisphosphatase, specifically in the pathway of gluconeogenesis?
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What is the name of the cycle where lactate from muscle is converted into glucose in the liver?
What is the name of the cycle where lactate from muscle is converted into glucose in the liver?
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Study Notes
Gluconeogenesis
- Gluconeogenesis is the synthesis of glucose from non-carbohydrate precursors
- The liver is the major site for gluconeogenesis, with the kidney playing a minor role
- Brain, muscle have very little gluconeogenic activity
- Gluconeogenesis is important in fasting, starvation, and strenuous activity
- Key precursors include pyruvate, lactate, glycerol, and propionyl CoA
Learning Outcomes
- Students will be able to define gluconeogenesis
- Students will be able to describe the pathways for converting pyruvate to glucose
- Students will understand the Cori cycle
- Students will be able to explain the conversion of glycerol to glucose
- Students will know how propionic acid is converted to glucose.
- Students will understand hormonal regulation of gluconeogenesis
- Students will be able to explain the regulation of key enzymes in gluconeogenesis
Methods of Gluconeogenesis
- Pyruvate → Glucose: The conversion of pyruvate to glucose involves the bypass of glycolytic reactions.
- Lactate → Glucose (Cori Cycle): Lactate, produced during anaerobic glycolysis in muscle, is transported to the liver for glucose synthesis.
- Glycerol → Glucose: Glycerol, derived from the hydrolysis of triglycerides, enters gluconeogenesis after phosphorylation.
- Propionyl CoA → Glucose: Propionic acid, is primarily synthesized in ruminants, converted to propionyl CoA, before being utilized in gluconeogenesis
Sources of Precursors
- Pyruvate/OAA: Amino acids (AAs) from muscle protein breakdown are deaminated and converted into gluconeogenic precursors in the liver.
- Lactate: Primarily produced in muscle cells during anaerobic glycolysis.
- Glycerol: Derived from the hydrolysis of triglycerides stored in adipose tissue.
- Propionic Acid: Synthesized largely by ruminants
Bypass of Glycolysis
- The conversion of pyruvate to PEP, fructose-1,6-biP to fructose-6-P and G6P to glucose involves the bypass of irreversible reactions that occur in glycolysis.
Gluconeogenesis Enzymes
- Pyruvate carboxylase
- Phosphoenolpyruvate carboxylase
- Fructose-1,6-biphosphatase
- Glucose-6-phosphatase
- Other enzymes such as cytoplasmic PEP carboxykinase, cytosolic malate dehydrogenase, and pyruvate carboxylase
Cori Cycle
- The Cori cycle describes the reciprocal relationship between lactate production in muscle and glucose production in the liver.
- Lactate produced by muscle during anaerobic conditions is transported to the liver, where it is converted back to glucose.
- This cycle ensures a continuous supply of glucose to the muscle during periods of high activity.
Glycerol → Glucose
- Glycerol, a byproduct of triglyceride breakdown, is phosphorylated and converted to glyceraldehyde-3P, an intermediary in glycolysis and gluconeogenesis.
Propionyl CoA → Glucose
- Propionyl CoA, derived from certain amino acids and fatty acids, is converted to succinyl-CoA
- Then, succinyl-CoA enters the citric acid cycle which generates pyruvate for gluconeogenesis
Hormonal Regulation
- Glucagon promotes gluconeogenesis
- Insulin inhibits gluconeogenesis
- Hormonal regulation affects the transcription rate and degradation rate of mRNA for key enzymes involved and the regulation of F-2,6-BP
F-2,6-BP
- Fructose 2,6-bisphosphate stimulates phosphofructokinase, and inhibits fructose-1,6-bisphosphatase
- Its concentration is controlled by insulin and glucagon
- This reflects the cell's energy status
Summary of Gluconeogenesis Regulation
- Regulation is influenced by hormones (glucagon, insulin), and metabolites (e.g., fructose 2,6-bisphosphate)
- Affecting enzyme activity, mRNA levels, and other regulatory processes.
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Description
This quiz focuses on the process of gluconeogenesis, highlighting its significance in glucose synthesis from non-carbohydrate sources. Students will explore the key precursors, regulatory mechanisms, and pathways involved in gluconeogenesis, as well as the role of the liver and kidney in this metabolic process.
