Chapter 16B: Gluconeogenesis
How does acetyl-CoA affect the activity of pyruvate kinase? Pyruvate dehydrogenase? Pyruvate carboxylase?
Acetyl-CoA inhibits pyruvate kinase and pyruvate dehydrogenase and activates pyruvate carboxylase.
Is fructose-1,6-bisphophatase active when the cell's energy is high or low? Why?
Fructose-1,6-bisphosphatase is active when energy in the cell is high because it will help make glucose that can be stored in glycogen for energy use when needed.
What inhibits fructose-1,6-bisphosphatase? What activates it?
Fructose-1,6-bisphosphatase is allosterically inhibited by AMP and activated by citrate. These substrates have the opposite effects on phosphofructokinase.
What are the products and reactants of the formation of fructose-6-phosphate from fructose-1,6-bisphosphate?
Fructose-1,6-bisphosphate and a water molecule react with fructose-1,6-bisphosphatase to form fructose-6-phosphate and an inorganic phosphate molecule.
How is glucose-6-phosphatase regulated?
Glucose-6-phosphatase isn't allosterically inhibited. Instead, it has a high Km (i.e., low affinity) for glucose-6-phosphate. Glucose-6-phosphate inhibits hexokinase. Thus, glucose-6-phosphatase is only active when glucose-6-phosphate levels are high, which also inhibit hexokinase.
What are the products, reactants, and enzyme involved in the formation of PEP from oxaloacetate?
Oxaloacetate and GTP react with PEP carboxykinase to form PEP, GDP, and carbon dioxide.
What is oxaloacetate converted into during gluconeogenesis? Why?
Oxaloacetate is converted to malate, which can leave the mitochondria and be transported to the cytoplasm. Once in the cytoplasm, malate converts back to oxaloacetate.
Is pyruvate carboxylase active when the cell's energy is high or low? Why?
Pyruvate carboxylase is active when energy in the cell is high because pyruvate carboxylase begins gluconeogenesis which will make glucose that can be stored in glycogen for energy use when needed.
What are the products, reactants, and enzyme of the formation of oxaloacetate from pyruvate?
Pyruvate, bicarbonate, and ATP react with pyruvate carboxylase to yield oxaloacetate, ADP, and P.
What is gluconeogensis?
The production of new glucose molecules.
What reactions are not reversible in glycolysis, and what enzymes in gluconeogenesis carry out the reverse reaction?
The reaction of PEP to pyruvate is not reversible. The enzymes pyruvate carboxylase and PEP carboxykinase carry out the reactions that convert pyruvate to oxaloacetate and then to PEP. The reaction of fructose-6-phosphate to fructose-1,6-bisphosphate is not directly reversed. The enzyme fructose-1,6-bisphophatase converts fructose-1,6-bisphosphate to fructose-6-phosphate. The reaction of glucose to glucose-6-phosphate is not directly reversed. The enzyme glucose-6-phosphatase converts glucose-6-phosphate to glucose.
The presence of high concentrations of what molecules are indicators that a cell is in need of energy?
AMP and ADP.
The presence of high concentration of which molecules are indicators that a cell has plenty of energy available?
ATP, citrate, and acetyl-CoA.
What two molecules are allosteric activators of pyruvate carboxylase?
Acetyl-CoA and ATP. If these molecules have a high concentration, then there is plenty of energy in the cell. This reaction is activated so that pyruvate is made into glucose and perhaps glycogen. When acetyl-CoA and ATP levels are low, this reaction is inhibited so that pyruvate is shuttled into the Krebs Cycle to produce more ATP.
What donates a carbon to pyruvate when it's carboxylated to oxaloacetate in gluconeogenesis via pyruvate carboxylase?
Bicarbonate.
What is the coenzyme of pyruvate carboxylase?
Biotin.
What stimulates activity of fructose-1,6-phosphatase? What two molecules inhibit its activity?
Citrate stimulates its activity. Fructose-2,6-bisphosphate and AMP inhibit its activity.
What are the products and reactants of the formation of glucose from glucose-6-phosphate?
Glucose-6-phosphate reacts with glucose-6-phosphatase to form glucose and an inorganic phosphate molecule.
When the cell's energy level is low, will glycolysis or gluconeogenesis be active?
Glycolysis.
Converting lactate to pyruvate in the Cori Cycle requires what?
In order to convert lactate to pyruvate, NAD+ is reduced to NADH.
Where in the cell is glucose-6-phosphatase found? How does this step of gluconeogenesis occur?
In the endoplasmic reticulum. Transporter 1 takes glucose-6-phosphate into the endoplasmic reticulum, where glucose-6-phosphatase hydrolyzes it to glucose and an inorganic phosphate, which are transported to the cytosol by T2 and T3, respectively. Glucose is then exported to the bloodstream.
What reaction does fructose-1,6-bisphosphatase catalyze?
It catalyzes the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate.
What reaction does pyruvate carboxylase catalyze?
It catalyzes the conversion of pyruvate to oxaloacetate.
What reaction does glucose-6-phosphatase catalyze?
It catalyzes the formation of glucose from glucose-6-phosphate.
Where does the conversion of pyruvate to oxaloacetate occur in the cell?
It occurs in the mitochondria.
What might a person with a mutation to the glucose-6-phosphatase enzyme that renders the enzyme ineffective experience?
This person might experience hypoglycemia because the liver can't create glucose via gluconeogenesis.
In which steps of gluconeogenesis are ATP, GTP, and NADH used?
To convert pyruvate to oxaloacetate, one ATP molecule is used. To convert oxaloacetate to PEP, one GTP molecule is used. To convert 3-phosphoglycerate to 1,3-bisphosphoglycerate, one molecule of ATP is used. To convert 1,3-bisphosphoglycerate to G3P, one molecule of NADH is used.
What is the overall reaction for converting pyruvate to glucose?
Two pyruvate molecules, four ATP's, two GTP's, two NADH's, two protons, and six water molecules yield a glucose molecule, four ADP's, two GDP's, six inorganic phosphates, and two NAD+'s.
