17. Gluconeogenesis Pathway (GNG). Substrates of GNG. Intertissue Connections: The Lactic Acid (Cori) Cycle.
Covers gluconeogenesis as glucose synthesis from non-carbohydrate precursors, mainly in the liver and to a lesser degree in the renal cortex, and why it matters during fasting. It then lists the substrates lactate, alanine, glycerol, propionate and TCA intermediates, the cellular locations of the steps, and the bypass enzymes that get around glycolysis's irreversible reactions. It closes with energy cost, hormonal control, the Cori cycle, and clinical links such as hypoglycaemia, alcohol intoxication and biotin deficiency.
Topic 17 of 76 in the MU Pleven syllabus for Biochemistry (Medicine, Year 2). The free AceMed note covers it in 8 sections, about 385 words (3 min of reading), with 10 flashcards.
In this note
Gluconeogenesis Pathway (GNG).
Gluconeogenesis (GNG)
Substrates (Precursors) of Gluconeogenesis
Location of Reactions
Main Reactions / Key Bypass Steps
Energy Requirement
Inter-Tissue Connection: The Lactic Acid (Cori) Cycle
Clinical Significance
Gluconeogenesis (GNG)
Definition
Gluconeogenesis is the metabolic pathway that synthesizes glucose from non-carbohydrate precursors, mainly in the liver and to a lesser degree in the renal cortex.
It ensures a continuous supply of glucose during fasting, starvation, low-carbohydrate diets, prolonged exercise, or fetal growth.
Major Site(s)
Liver (primary site).
Kidneys (significant role during prolonged fasting).
Importance
Maintains blood glucose homeostasis during fasting.
Supplies glucose to glucose-dependent tissues like brain, RBCs, renal medulla, lens, testes, exercising muscle.
Substrates (Precursors) of Gluconeogenesis
Lactate
From anaerobic glycolysis in RBCs and exercising skeletal muscle.
Converted to pyruvate in the liver.
Alanine (and other glucogenic amino acids)
From muscle proteolysis during fasting.
Transamination converts alanine → pyruvate.
Glycerol
Released from lipolysis of triglycerides in adipose tissue.
Converted to dihydroxyacetone phosphate (DHAP) in the liver.
Propionate
From odd-chain fatty acid oxidation (minor contribution).
TCA Cycle Intermediates
Many intermediates can be converted to oxaloacetate and enter GNG
