Gluconeogenesis

• Glucose is the primary source of energy for most cells.
• The liver can convert non-carbohydrate sources into glucose through gluconeogenesis, which occurs when blood glucose levels are low or insulin levels are high.
• Liver stores about 100 grams of glycogen at any given time.
• Liver stores about 10% of total body carbohydrates as glycogen.
• Muscle tissue also contains glycogen, but it accounts for only 2% of total body carbohydrates.
• Glycogenolysis is the breakdown of stored glycogen to release glucose molecules.
• Pyruvic acid is converted into acetyl CoA by oxidative decarboxylation.
• Acetyl CoA enters the citric acid cycle (Krebs cycle) and produces ATP.
• Gluconeogenesis involves converting pyruvate from lactate, amino acids, and fatty acids into glucose.
• In gluconeogenesis, pyruvate is first converted into oxaloacetic acid using carbon dioxide.
• Gluconeogenesis occurs when blood glucose levels are low due to fasting, exercise, or stress.
• In the absence of dietary carbohydrates, the liver uses gluconeogenesis to maintain normal blood glucose concentrations.
• During fasting, the liver breaks down fats and proteins to generate energy and synthesize glucose via gluconeogenesis.
• Oxaloacetic acid is then reduced to malic acid through NADH-dependent reduction.
• Malic acid is converted back to pyruvic acid via dehydrogenation with FAD as an electron acceptor.
• The resulting pyruvic acid can be used for gluconeogenesis or enter the Krebs cycle.
• Muscle cells can also use gluconeogenesis to produce glucose for energy production.
• The liver uses gluconeogenesis to maintain normal blood sugar levels during periods of low carbohydrate intake.
• The process of glycogenolysis releases glucose-1-phosphate, which can be further processed through phosphoglucomutase to form glucose-6-phosphate.
• Glucose-6-phosphatase catalyzes the conversion of glucose-6-phosphate to free glucose, allowing it to enter the bloodstream.
• Galactose is metabolized similarly to glucose, with galactokinase adding a phosphate group to convert galactose to galactose-1-phosphate.
• The process of glycogenolysis releases glucose molecules stored as glycogen in the liver and muscles.
• Pyruvate is produced during glycolysis and can be further metabolized through aerobic respiration if sufficient oxygen is available.
• Malic acid is decarboxylated by Malic Enzyme (ME) to produce Pyruvate and CO2.
• Pyruvate is transported out of mitochondria and converted back to PEP by Pyruvate Kinase (PK).
• PEP is phosphorylated by Phosphoenolpyruvate Carboxykinase (PEPCK) to form Oxaloacetate.
• Pyruvic acid is decarboxylated by pyruvate carboxylase to form acetyl CoA.
• Pyruvate carboxylase catalyzes the conversion of pyruvate into oxaloacetate using biotin as a cofactor.
• Phosphoenolpyruvate (PEP) is produced from pyruvate through decarboxylation and phosphorylation reactions.
• Gluconeogenesis occurs primarily in the liver but can occur in other tissues such as muscle cells during prolonged exercise.
• Noncarbohydrate precursors include lactate, glycerol, amino acids (alanine), and fatty acids.
• Gluconeogenesis occurs primarily in the liver but can occur in other tissues such as muscle cells under certain conditions.
• In the absence of insulin, glycogenolysis predominates over gluconeogenesis.
• Insulin stimulates glucose uptake by target organs (muscles) and inhibits hepatic glucose release.
• Glucose-6-phosphatase catalyzes the removal of the phosphate group from glucose-6-phosphate, producing free glucose that enters the bloodstream.
• Glycolysis occurs in the cytoplasm of all cells except red blood cells (RBC), while gluconeogenesis takes place only in the liver and kidneys.
• In RBCs, there are no mitochondria, so they cannot perform oxidative metabolism.
• Pyruvate produced by glycolysis enters the mitochondria and undergoes oxidative decarboxylation to become acetyl CoA.
• Acetyl CoA enters the citric acid cycle (Krebs cycle) and generates more ATP.
• Uridine diphospho (UDP) galactose transfers its galactose moiety from UDP to glucose-1-phosphate, forming uridine diphosphate (UDP).