Lecture 21 Gluconeogenesis Flashcards
Describe the body’s needs for glucose
The whole body needs 160 g of glucose a day
brain requires 120 g of glucose
glucose that is present in the body fluid is 20 g
the glucose that is available from glycogen is 190g that can serve the body for about a day obviously
Describe gluconeogensis; the basics
occurs in the liver and kidney
makes glucose from non-carbohydrate (pyruvate)
It is NOT just a reversal of glycolysis
What are the precursors for gluconeogenesis?
lactate
amino acids
glycerol
Why is gluconeogenesis not a reversal of glycolysis?
Because there are irreversible steps that have to be overcome, like…..
- pyruvate kinase
- hexokinase
- PFK-1
What are the enzymes that are present in gluconeogenesis that are NOT present in glycolysis
- Pyruvate carboxylase
- phosphoenolpyruvate carboxykinase
- Fructose 1,6-bisphosphatase
- Glucose-6-phosphatase
Describe the process of pyruvate turning into phosphoenolpyruvate
Pyruvate carboxylase takes the pyruvate to the oxaloacetate with the help of ATP
phosphoenoopyruvate carboxykinase takes oxaloacetate to phosphoenolpyruvate with the help of GTP
Describe how OAA (oxaloacetate) is able to get to the site of gluconeogenesis?
After glycolysis happens, the pyruvate is is taken to the mitochondria where the pyruvate carboxylase converts it into OAA, which is transported out of the mitochondria via the malate shuttle, which uses NAD+
Describe how F1,6BP gets to fructose 6 phosphate
Fructose 1,6 bisphosphatase removes the phosphate from the molecule with the help of water
Describe how Glucose-6-phosphate to glucose
Glucose-6-phosphatase takes glucose 6 phosphate to glucose with the help of water and the phosphate
Describe the actions of Glucose 6-phosphatase
Glucose 6 phosphatase is an enzyme that is in the lumen of the endoplasmic reticulum
T1 transports G6P to the ER
T2 transports inorganic phosphate to the cytosol
T3 takes the glucose back into the cytoplasm
What determines what pathway will happen? (gluconeogenesis or glycolysis?)
Energy charge (ATP/ADP ratio) determines which pathway will be most active
What are the activators of Phosphofructokinase in glycolysis?
F26BP
AMP
What are the activators of Pyruvate kinase in glycolysis?
F16BP
What are the inhibitors of phosphofructokinase in glycolysis?
ATP, citrate, H+
What are the inhibitors of pyruvate kinase in glycolysis
ATP
Alanine
What are the activators of Fructose 16 BP in gluconeogenesis?
Citrate
What are the activators of pyruvate carboxylase?
Acetyl CoA
What are the inhibitors of pyruvate carboxylase?
ADP
What are the inhibitors of phosphoenolpyruvate carboxykinase?
ADP
Describe the regulation of glycolysis and gluconeogenesis in the liver
The liver chooses the pathways based on what is needed to maintain the blood glucose
Describe the role of Fructose 2,6 bisphosphatase in glycolysis and gluconeogenesis
stimulates PFK, which takes Glucose 6 phosphate to Fructose 6 phosphate
inhibits fructose 1,6-bisphosphatase
What are the two enzymes that regulate the concentration of F26BP
phosphofructokinase 2 (PFK2) and fructose bisphosphatase (FBPase2)
Describe the Cori cycle
The process of recycling glucose and lactate from the muscle and the liver via the blood stream.
In the muscle, glycolysis is used to make pyruvate and then lactate which is transferred into the blood stream that can go into the liver and undergoes gluconeogenesis to make glucose which then goes into the blood and back to the muscle
Say that you are sprinting, describe what your body will do in order to keep the metabolism.
- glycolysis occurs in the muscles
- gluconeogenesis occurs in the liver
- lactic acid fermentation occurs in the muscle cells and takes pyruvate into lactate
- Citric acid cycle and oxidative phosphorylation occurs in the muscle cells to turn the pyruvate into CO2 and H2O
- glycogen breakdown occurs in the cardiac muscle cell and makes glucose for the body
- fatty acids oxidation occurs in the that takes glycogen into the glucose-6-phosphate
- amino acid catabolism takes amino acids into pyruvate
