Gluconeogenesis Lecture
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Questions and Answers

Which substrates are primarily used in gluconeogenesis?

  • Fatty acids and glucose
  • Acetyl-CoA and ketone bodies
  • Lactate, pyruvate, glycerol, and α-keto acids (correct)
  • Glucogenic and ketogenic amino acids

What is the primary organ responsible for gluconeogenesis during an overnight fast?

  • Adipose tissue
  • Muscles
  • Liver (correct)
  • Kidneys

How does the contribution of kidneys to gluconeogenesis change during prolonged fasting?

  • It becomes the exclusive source of glucose
  • It increases to approximately 40% (correct)
  • It decreases to 10% of total production
  • It remains constant at 10%

Which of the following is a major regulating substance for the gluconeogenesis process?

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

What is primarily responsible for the release of lactate into the bloodstream?

<p>Exercising skeletal muscle and certain cells lacking mitochondria (B)</p> Signup and view all the answers

What role does lactate play in the process of gluconeogenesis?

<p>It is converted back to glucose in the liver. (D)</p> Signup and view all the answers

Which enzyme is primarily activated by glucagon to stimulate gluconeogenesis?

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

What effect does acetyl CoA have on gluconeogenesis during fasting?

<p>It activates hepatic pyruvate carboxylase. (C)</p> Signup and view all the answers

How does insulin influence gluconeogenesis?

<p>Inhibits mobilization of amino acids from proteins (C)</p> Signup and view all the answers

Which statement accurately describes the role of fructose 1,6-bisphosphatase in gluconeogenesis?

<p>It is a rate-limiting enzyme in gluconeogenesis. (C)</p> Signup and view all the answers

What is the result of lactate accumulation during strenuous exercise?

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

Which enzyme is activated by glucagon to promote gluconeogenesis?

<p>Fructose-1,6-bisphosphatase (A), PEP-carboxykinase (D)</p> Signup and view all the answers

What is the primary role of α-keto acids in gluconeogenesis?

<p>Enter the TCA cycle to form oxaloacetate (C)</p> Signup and view all the answers

How does acetyl CoA influence gluconeogenesis during fasting?

<p>Stimulates hepatic pyruvate carboxylase (C)</p> Signup and view all the answers

What effect does insulin have on amino acid mobilization from tissues?

<p>It inhibits the mobilization of amino acids (D)</p> Signup and view all the answers

What is the major source of glucose for the body during the initial phase of fasting?

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

Which of the following tissues contributes significantly to gluconeogenesis during prolonged fasting?

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

Which substance is derived from the hydrolysis of triacylglycerols and used in gluconeogenesis?

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

Which of the following statements is true regarding the contribution of the liver and kidneys to gluconeogenesis?

<p>Approximately 90% of gluconeogenesis occurs in the liver during the overnight fast. (C)</p> Signup and view all the answers

In which cycle is lactate produced during exercise converted back to glucose?

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

Flashcards

Gluconeogenesis function

The process of synthesizing glucose from non-carbohydrate precursors.

Gluconeogenesis substrates

Molecules like lactate, glycerol, and certain amino acids that supply carbon atoms for glucose production.

Glycerol as Gluconeogenic Substrates

Glycerol, derived from fat breakdown, is a key source of carbon atoms for glucose synthesis.

Lactate as Gluconeogenic Substrate

Lactate, produced by muscle during exertion, is an important gluconeogenic precursor.

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Key organs for Gluconeogenesis

During prolonged fasting, kidneys become major producers of glucose; livers are also crucial for glucose production.

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Gluconeogenesis:

The process of producing glucose from non-carbohydrate sources like amino acids and lactate.

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Gluconeogenic substrates

Molecules like lactate or amino acids that provide the building blocks for glucose synthesis in the liver.

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Lactate as gluconeogenic substrate

Lactate, produced during muscle exertion, is converted back to glucose in the liver.

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Glucagon's role in Gluconeogenesis

Glucagon stimulates gluconeogenesis by activating enzymes and increasing the production of PEP-carboxykinase.

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Regulation of Gluconeogenesis via Substrate availability

The amount of available gluconeogenic precursors (like amino acids) directly affects the rate of glucose synthesis.

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Gluconeogenesis

The process of making new glucose from non-carbohydrate sources.

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Gluconeogenesis Substrates

Lactate, glycerol, and certain amino acids that provide carbon atoms for glucose.

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Glycerol (Gluconeogenesis)

A fat breakdown product, important for glucose creation.

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Lactate (Gluconeogenesis)

Muscle exertion byproduct that helps make glucose.

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Kidney's Role in Gluconeogenesis

Plays a significant role in glucose production during longer fasts.

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Lactate's role in gluconeogenesis

Lactate, produced during exercise, is converted back to glucose in the liver.

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Gluconeogenesis and Glucagon

Glucagon, a hormone, stimulates gluconeogenesis by affecting enzymes.

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Gluconeogenesis substrates

Molecules like amino acids and lactate that create glucose.

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PEP-carboxykinase

An enzyme crucial for gluconeogenesis; its activity is regulated by hormones.

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Gluconeogenesis regulation: Substrate availability

The amount of available gluconeogenic precursors like amino acids controls glucose synthesis.

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Study Notes

Gluconeogenesis Lecture

  • Gluconeogenesis is the process of forming glucose from non-carbohydrate precursors
  • Certain tissues (brain, red blood cells, kidney medulla, eye lens/cornea, testes, exercising muscle) continuously need glucose for metabolic fuel.
  • Liver glycogen is a primary source of glucose during the post-meal period and can meet needs for about 10-18 hours.
  • During prolonged fasting, gluconeogenesis takes over, forming glucose from precursors like lactate, pyruvate, glycerol (from triacylglycerols), and α-keto acids (from glucogenic amino acids).
  • Gluconeogenesis requires both mitochondrial and cytosolic enzymes.
  • Approximately 90% of overnight gluconeogenesis occurs in the liver, with the kidney contributing 10%.
  • During prolonged fasting, the kidney becomes a major glucose-producing organ, contributing 40% of total glucose production.
  • Gluconeogenic precursors are molecules used to make glucose; examples include intermediates from the tricarboxylic acid (TCA) cycle and glycolysis, glycerol, lactate, and α-keto acids from transamination of glucogenic amino acids.
  • Glycerol, released from triacylglycerol breakdown in adipose tissue, is transported to the liver, converted to glycerol-3-phosphate, and used in gluconeogenesis.
  • Lactate is produced by exercising muscle and anaerobic cells (e.g., red blood cells), transported to the liver, converted to glucose, and released back to the bloodstream. (Cori cycle).
  • Amino acids derived from tissue protein hydrolysis fuel gluconeogenesis. Alpha-keto acids (e.g., α-ketoglutarate) from amino acid metabolism enter the TCA cycle to form oxaloacetate, a precursor for phosphoenolpyruvate.

Key Enzymes for Gluconeogenesis

  • Key enzymes include PEP-carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase.

Regulation of Gluconeogenesis

  • Glucagon: Stimulates gluconeogenesis by activating fructose-1,6-bisphosphatase and increasing PEP-carboxykinase gene transcription.
  • Insulin: Inhibits gluconeogenesis by decreasing mRNA transcription for PEP-carboxykinase.
  • Substrate Availability: The availability of gluconeogenic precursors, notably glucogenic amino acids, significantly impacts hepatic glucose synthesis. Insulin inhibits mobilization of amino acids from tissue protein.
  • Allosteric activation by acetyl-CoA: Accumulation of acetyl-CoA during prolonged fasting activates hepatic pyruvate carboxylase.
  • Allosteric inhibition by AMP: Fructose 1,6-bisphosphatase is inhibited by AMP, a molecule that activates phosphofructokinase-1 (glycolysis enzyme).

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Description

This quiz covers the essential aspects of gluconeogenesis, the metabolic pathway that synthesizes glucose from non-carbohydrate sources. It examines the roles of different tissues in glucose metabolism and highlights the significance of gluconeogenesis during fasting periods. Test your understanding of this vital physiological process!

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