GLUCONEOGENESIS Flashcards
Define gluconeogenesis
Gluconeogenesis is the process of converting non carbohydrates precursors such as lactate, glycerol and glucogenic amino acids to glucose.
What is the function of gluconeogenesis during stravation?
During starvation, the amount of glucose level in the blood is low. To ensure that the blood glucose level is well maintained, gluconeogenesis is needed.
What is the function of gluconeogenesis during extended exercise?
During extended exercise, when carbohydrates and lipid reserves are mobilised, gluconeogenesis allows the lactate from the TCA cycle and glycerol from fat breakdown to convert to glucose.
Where does gluconeogenesis mainly occur?
In the liver and kidney
State 4 precursors of gluconegenesis.
- Lactate
- Alanine
- Glucogenic amino acid
- Glycerol
Which reactions from glycolysis are bypassed in gluconeogenesis?
Irreversible reaction:
- Glucose to glucose-6-phosphate
- Fructose-6-phosphate to fructose-1,6-biphosphate
What does it requires to convert 2 moles of pyruvate to form 1 mole of glucose?
- 4 moles of ATP
- 2 moles of GTP
- 2 moles of NADH
Briefly explain the gluconeogenesis in the Cori Cycle.
- Cori cycle happened during the anaerobic glycolysis.
- The pyruvate formed from the glucose in the glycolysis pathway are converted to lactate by lactate dehydrogenase (LDH)
- The lactate then released in to the blood stream and transported into the liver.
- The lactate is converted to pyruvate by LDH.
- In the liver, the pyruvate is then converted to glucose via gluconeogenesis then is released into the blood
- Hence, it will act as an energy source for the muscles as well as other tissues.
Briefly describe the gluconeogenesis of alanine.
- Alanine is formed through the conversion of pyruvate in the glycolysis pathway by a transamination process.
- In fact, the conversion of pyruvate into alanine also occur during starvation.
- The alanine produced are released into the blood and then transported into the liver.
- In the liver, the alanine produced are going to convert back to pyruvate through the reverse reaction of transamination process.
- The pyruvate is then used in the formation of glucose via gluconeogenesis.
Describe the gluconeogenesis pathway starting from the pyruvate in the TCA cycle.
- In the mitochondrial matrix, the pyruvate is converted to oxaloacetate (OAA).
- The ATP is hydrolised and provide energy for carboxylation of pyruvate to occur.
- This process is catalysed by the pyruvate carboxylase.
- OAA cannot pass through the mitochondrial membrane.
- Due to that problem, the interconversion of OAA to malate is occur.
- OAA is converted to malate so it can pass through the mitochondrial membrane then returns back to OAA in the cytosol.
- This process is catalysed by the malate dehydrogenase.
- In the cytosol, the OAA is then catalysed by the phosphoenolpyruvate carboxylase (PEPCK) to convert to phosphoenolpyruvate (PEP)
- This protein obtain energy for the carboxylation of OAA from the hydrolysis of GTP.
- Next, PEP is then converted to fructose-1,6- biphosphate (F1,6BP)
- Then F1,6BP is then converted to fructose-6-phosphate (F6P) and is catalysed by the fructose 1,6-biphosphatase.
- In this process, Pi is released.
- Next, F6P is then converted to glucose-6-phosphate (G6P).
- Lastly, G6P is converted to glucose with the help from the glucose 6-phosphatase.
- Pi is released in this process.
When does gluconeogenesis occur?
- During starvation
- During prolonged exercise
- During high protein diet / under conditions of stress
What are the three(3) mechanisms that responsible for regulating the activity of enzyme in gluconeogenesis?
- changes in the rate of enzyme synthesis (induction/ repression)
- covalent modification by reversible phosphorylation
- allosteric effect
What does it mean by the ‘reciprocal regulation of gluconeogenesis and glycolysis in the liver’?
- Glycolysis and gluconeogenesis is reciprocally regulated.
- When glycolysis is turn on, the gluconeogenesis is turn off
- In a well fed state, the glycolysis is the only one activated.
- However, during starvation, gluconeogenesis is activated.
- Both process cannot occur at the same time.
Describe the regulation of gluconeogenesis by glucagon
- Low level blood glucose causes the level of glucagon secretion to increase.
- Simultaneously, this causes the amount of cAMP to be increase as well.
- The high amount of cAMP leads to high amount of enzyme phosphorylation.
- This resulting in the activation of FBPase 2 and inactivation of PFK 2.
- The level of F2,6P is decreases.
- Hence, gluconeogenesis increased.
State the difference of glycolysis and gluconeogenesis.
Glycolysis
- happen in the cytosol
- The regulatory enzymes are hexokinase, pyruvate kinase and phosphofructokinase-1 (PFK1)
Gluconeogenesis
- happen in the cytosol and mitochondrial matrix
- the regulatory enzyme are pyruvate carboxylase, fructose-1,6-biphosphatase and glucose-6-phosphatase
