Gluconeogenesis Flashcards
List 4 characteristics of Gluconeogenesis
- Synthesis of glucose from amino acids, glycerol and lactic acid
- Occurs in liver and kidney
- The only source of glucose during prolonged fasting to maintain blood glucose level
- Very important for brain and red blood cells as they cannot oxidize additional fuel besides glucose
What are the irreversible steps in glycolysis?
Hexokinase, phosphofructokinase and pyruvate kinase.
They all convert ADP to ATP in the process.
Gluconeogenesis
- Synthesis of glucose from non-carbohydrates sources.
- 2 pyruvate -> 1 glucose
- Requires 4 ATP + 2 GTP + 2 NADH for energy
- Liver - important in maintaining blood glucose during vigorous exercise and starvation
List 3 Sources for gluconeogenesis
Lactate from lactic acid fermentation in muscle
Glycerol from fat breakdown in adipose tissues
Amino acids from protein breakdown, amino acid pools in muscle during muscle degradation.
4 Distinct steps in gluconeogensis
To reverse hexokinase, we have glucose 6 phosphate
To reverse phosphofructokinase, we have fructose 1,6 bi-phosphate
To reverse pyruvate kinase, we have pyruvate decarboxylase and phospho-enol pyruvate decarboxylase.
Where are all enzymes of gluconeogenesis found
All are found in cytoplasm except pyruvate decarboxylase found in the mitochondria and glucose 6 phosphate found in the membrane bound to endoplasmic reticulum.
Hexokinase vs Glucose 6 phosphatase
Hexokinase catalyze conversion of glucose to glucose 6 phosphate.
Glucose 6 phosphatase catalyze conversion of glucose 6 phosphatase to glucose.
Phosphofructokinase vs Fructose 1,6 bi-phosphatase
Phosphofructokinase catalyze the conversion of fructose 6 phosphate to fructose 1,6 bi-phosphate.
Fructose 1,6 bi-phosphatase catalyze the conversion of fructose 1,6 bi-phosphate to fructose 6 phosphate
Pyruvate kinase vs pyruvate carboxylase and phosphoenol pyruvate carboxy-kinase
Phosphoenol pyruvate carboxykinase catalyze the conversion of oxaloacetate to phosphoenol pyruvate.
Pyruvate carboxylase catalyze the conversion of pyruvate to oxaloacetate.
Why glycolysis and gluconeogenesis cannot occur at the same time?
Both are regulated by enzymatic control via inhibition and activated and also via hormonal control such as insulin and glucagon.
However, glycolysis can occur immediately after gluconeogenesis.
Low energy will promote glycolysis. High energy will promote gluconeogenesis.
How is phosphofructokinase regulated in glycolysis?
Fructose 2,6 bi-phosphate and AMP activate phosphofructokinase
ATP citrate and H+ will inhibit phosphofructokinase.
When there is a lot of glucose, there will be a lot of fructose 2,6 bi-phosphate. AMP is a low energy molecule, meaning there needs to be energy produced.
ATP is a high energy molecule, meaning there needs to be less energy produced. Citrate level is high, glycolysis is high and Krebs Cycle is high. This process give a lot of energy and hence glycolysis rate needs to be reduced.
How is pyruvate kinase regulated in glycolysis?
Fructose 1,6 bi-phosphate activate pyruvate kinase
ATP and alanine will inhibit pyruvate kinase.
Fructose 1,6 bi-phosphate come before pyruvate and hence will activate it.
ATP is energy rich and when there is a lot of ATP< glycolysis rate have to be reduced.
Alanine can be interconverted to pyruvate. When there is a lot of pyruvate, there is a lot of alanine. Hence, alanine is used to inhibit pyruvate kinase to stop pyruvate production.
How is fructose 1,6 bi-phosphotase regulated
Fructose 2,6 bi-phosphate and AMP inhibits fructose 1,6 biphosphotase
Citrate activates fructose 1,6 bi-phosphotase.
How is phosphoenol-pyruvate carboxylase regulated
ADP inhibits phosphoenol pyruvate carboxylase.
How gluconeogenesis and glycolysis cannot occur at the same time?
Whatever inhibits glycolysis will activate gluconeogenesis and vice versa.
