BIOL2771 WK4 P1

Introduction to Gluconeogenesis

  • Acknowledgement of the traditional lands, respect to elders.

  • Definition: Gluconeogenesis is the biochemical process whereby glucose is synthesized from pyruvate or other substrates, occurring in all life forms including animals, plants, fungi, and microorganisms.

Learning Outcomes of the Lecture

  • Understand the importance of gluconeogenesis in cells.

  • Identify the reasons why gluconeogenesis is needed.

  • Familiarize with the key steps involved in gluconeogenesis.

  • Examine the energetics of gluconeogenesis as a metabolic pathway.

  • Apply the understanding of gluconeogenesis to real-world problem solving.

Importance of Gluconeogenesis

  • Overview of Carbohydrate Metabolism: Most carbohydrates consumed are eventually converted to glucose in the body.

  • Normal Blood Glucose Levels: Blood glucose concentrations are maintained within a range of 4-6 mmol/L.

    • Well-fed State: Blood glucose levels rise post-meal, resulting in:

    • Increased glycolysis, producing pyruvate, ATP, and NADH (essential for further ATP production).

    • Excess glucose stored as glycogen in liver and muscle cells for later energy needs.

  • Energy Dynamics in Fasting State: During fasting or between meals, blood glucose levels drop, necessitating glucose synthesis:

    • Critical Function: Maintaining blood glucose levels is essential for the brain and other organs.

    • Synthesis Sources: New glucose is synthesized from non-carbohydrate precursors:

    • Amino acids (from protein breakdown).

    • Lactate (from anaerobic respiration).

Precursors of Glucose in Gluconeogenesis

  • Key Substrates for Glucose Synthesis:

    • Common precursors include:

    • Lactate

    • Pyruvate

    • Glycerol

    • Glucogenic amino acids (e.g., alanine, glutamine).

  • Location of Gluconeogenesis in Mammals:

    • Primary site: Liver.

    • Secondary sites: Renal cortex and epithelial cells of the small intestine.

  • Process After Vigorous Exercise:

    • Anaerobic glycolysis in skeletal muscles produces lactate.

    • Lactate is converted to pyruvate and subsequently to glucose-6-phosphate, which can be further converted to glucose to restore blood glucose levels.

    • Excess glucose can be converted to glycogen for storage.

Gluconeogenesis in Plants and Microorganisms

  • Plants:

    • Carbon dioxide fixation occurs through photosynthesis, and various substrates like fats, proteins, and three-phosphoglycerate can produce glucose-6-phosphate which converts to glucose.

    • Stored as starch (a polysaccharide) or sucrose (a disaccharide) for energy and structural functions.

  • Microorganisms:

    • Utilize simple organic compounds (2 or 3-carbon molecules) as precursors, such as acetate, lactate, and propionate sourced from their growth mediums.

Glucogenic Amino Acids in Gluconeogenesis

  • Key Amino Acids: Primarily includes alanine and glutamine.

    • Process: Amino group is removed from glucogenic amino acids, allowing their conversion to glucose-6-phosphate and ultimately to glucose.

Variation of Reactions Across Different Organisms

  • Although the fundamental reactions in gluconeogenesis are conserved across all organisms, metabolic contexts and pathway regulation may differ:

    • Species-specific regulation in pathways.

    • Tissue-specific variations in gluconeogenesis rates and mechanisms.

Key Steps of Gluconeogenesis

  • The detailed discussion of the key steps involved in the metabolic pathway of gluconeogenesis will be addressed in the following video lecture.

    • Importance of understanding each step in glucose synthesis and the biochemical processes involved.