Chapter 4-3. Glucose Synthesis
Higher category: 【Biology】 Chapter 4. Cell and Energy Metabolism
2. Cori cycle
a. Glycolysis
1. Gluconeogenesis
⑴ Overview
① Gluconeogenesis: Reverse Process of Glycolysis.
② Animal Cells: Occurs in the liver.
③ Hormonal Regulation
○ Glucagon, Glucocorticoid: Promote gluconeogenesis.
○ Insulin: Inhibits gluconeogenesis.
④ Leucine, Lysine: These two amino acids cannot undergo gluconeogenesis from amino acids.
⑤ Drinking alcohol without eating inhibits gluconeogenesis, leading to an increase in ketone bodies.
⑵ Conversion of Pyruvate to OAA (Oxaloacetic Acid)
① Enzyme: Pyruvate Carboxylase, located inside the mitochondria.
② Negative Feedback: Acetyl-CoA promotes pyruvate carboxylase → increases gluconeogenesis, decreases glycolysis → decreases acetyl-CoA
⑶ Conversion of OAA to PEP
① Enzyme: PEP Carboxykinase, located in the cytoplasm.
② Uses 1 GTP per OAA molecule.
○ Glycolysis: -2 ATP, +4 ATP
○ To produce one molecule of glucose: 2 GTP (OAA → PEP) + 4 ATP, a total of 6 NTPs are used.
⑷ Conversion of Fructose 1,6-bisphosphate to Fructose 6-phosphate
① Enzyme: Fructose-1,6-bisphosphatase (FBPase), located in the cytoplasm.
○ Enzyme for the reverse reaction: PFK-1, located in the cytoplasm.
② Allosteric regulation of the enzyme: Fructose-2,6-bisphosphate is inhibited, glucagon is promoted, and insulin is inhibited.
⑸ Conversion of Glucose 6-phosphate to Glucose
① Enzyme: Glucose-6-phosphatase, located in the smooth endoplasmic reticulum.
○ Enzyme for the reverse reaction: Hexokinase, located in the cytoplasm.
⑹ Conversion of Glucose 6-phosphate to Glucose 1-phosphate
① Enzyme for the reverse reaction: Phosphoglucomutase converts G-1-P to G-6-P.
⑺ Glucose 1-phosphate
① Added to the 4th or 6th carbon of the glycogen chain through a dehydration reaction.
② Enzyme for the reverse reaction: Glycogen Phosphorylase breaks down glycogen to G-1-P.
③ Insulin: Promotes dephosphorylation.
④ Glucagon: Promotes phosphorylation.
⑻ Action of Insulin
① 1st. When blood glucose levels are high, insulin binds to IR (insulin receptor).
② 2nd. This complex activates protein kinase through IRS-Pi and phosphorylates and inactivates glycogen synthase kinase.
③ 3rd. PP1 (protein phosphatase 1) dephosphorylates and activates glycogen synthase.
④ 4th. As a result, glycogen synthesis increases, lowering blood glucose levels.
2. Cori cycle
⑴ Overview
① Gluconeogenesis from lactic acid, which takes place in liver.
② There is no gluconeogenesis from alcohol.
⑵ Process: 4 ATP are consumed per cycle.
① The liver sends glucose to skeletal muscle.
② Skeletal muscle produces lactic acid.
○ Occurs frequently in red blood cells and type 2 muscles.
○ Does not occur in the heart or kidneys.
○ 2 ATP are produced.
③ Generated lactic acid is sent back to the liver.
④ Liver synthesize glucose.
○ 6 ATP are consumed.
⑶ When actively exercising,
① Skeletal muscle
○ During running, glycolysis is active, and NADH → NAD+ (i.e., lactic acid fermentation) is a slow reaction, so NAD+/NADH levels decrease.
○ After exercise, NAD+ and NADH concentrations return to normal, meaning NAD+/NADH levels increase.
② Liver: In liver, glycolysis normally takes place so that NAD+/NADH gets high.
3. Glyoxylate acid cycle
⑴ Definition: Glucose synthesis pathway of plants.
⑵ Place: Occurs through lipid body, glyoxisome, and mitochondria.
Input: 2019.01.16 17:47