Flashcards in Lecture 33 Deck (15)
Where does gluconeogenesis occur?
Gluconeogenesis only occurs in the liver and kidney
What is gluconeogenesis?
Gluconeogenesis is the formation of glucose from non-carbohydrate precursors
What is the first step of gluconeogenesis?
1) Pyruvate --> Oxaloacetate
2) Requires biotin, CO2, acetyl CoA, & ATP
a) Biotin attaches to the enzyme
b) ATP & Acetyl CoA allosterically activate the biotin-enzyme complex to bind to CO2
c) CO2 is then transferred to pyruvate to form oxaloacetate
3) Pyruvate carboxylase is the enzyme that catalyzes this reaction
4) This is the only reaction between glycolysis and gluconeogenesis that occurs in the mitochondria
What must happen before the second step of gluconeogenesis begins?
1) Oxaloacetate cannot cross the mitochondrial membrane, therefore it must be reduced
2) Oxaloacetate is reduced to Malate by the oxidation of NADH --> NAD+
3) Malate crosses the mitochondrial membrane and is the oxidized (by malate dehydrogenase) to reform oxaloacetate
What is the second step of gluconeogenesis?
1) Oxaloacetate --> PEP (Phosphoenol pyruvate)
2) GTP is required
3) PEP Carboxykinase is the enzyme that catalyzes this reaction
What is the third major step of gluconeogenesis?
1) After PEP is converted to Fructose-1,6-bisphosphate, Fructose-1,6-bisphosphate reacts with H2O to form Fructose-6-phosphate
2) Citrate stimulates this reaction
3) AMP & fructose-2,6-biphosphate inhibit this reaction
4) Fructose-1,6-bisphophatase is the enzyme that catalyzes this reaction
What is the fourth major step of gluconeogenesis?
1) Fructose-6-phosphate --> Glucose-6-phosphate followed by Glucose-6-phosphate + H2O --> Glucose
2) High levels of glucose inhibit the conversion of Glucose-6-phosphate to glucose
3) Glucose 6-phosphatase catalyzes the conversion of G6P to glucose
How does insulin lower blood glucose levels?
Insulin inhibits PEP carboxykinase, which prevents the formation of PEP (Phosphoenol pyruvate), and it inhibits Glucose-6-phosphatase, which prevents the formation of glucose
How does cortisol increase levels of blood glucose?
Cortisol increases the production of Glucose-6-phosphatase + PEP Carboxykinase
How does glucagon increase blood glucose levels?
Glucagon stimulates gluconeogenesis by decreasing levels of fructose-2,6-bisphosphate (broken down through ATP phosphorylation of the enzyme). This prevents the inhibition of Fructose-1,6-bisphosphate from being converted to F6P
Which amino acids can be used to form pyruvate?
Which amino acids can be used to form alpha keto glutarate?
Which amino acids can be used to form succinate?
What are three substrates that can be used to form glucose through gluconeogenesis?
1) Amino acids