Chapter 4-3. Synthesizing Glucose
Higher category : 【Biology】 Chapter 4. Cell and energy metabolism
2. Cori cycle
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 Enzyme Allosteric Regulation: Inhibited by fructose 2,6-bisphosphate, promoted by glucagon, inhibited by insulin
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: Added to the 4th or 6th carbon of glycogen chain via dehydration synthesis
① Enzyme for the reverse reaction: Glycogen Phosphorylase breaks down glycogen to G-1-P
② Insulin: Promotes dephosphorylation
③ 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 Gluconeogenesis from lactic acid, which takes place in liver.
① There is no gluconeogenesis from alcohol.
⑵ Process
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, mitochondria.
Input: 2019.01.16 17:47