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17 Cards in this Set

  • Front
  • Back
What reaction does pyruvate kinase catalyze?

Where is this reaction in glycolysis?
phosphoenolpyruvate +ADP-->Pyruvate + ATP

At the end
What are the roles of the liver and muscle in our bodies and what is the role of glucose metabolism in each?
Liver regulates glucose levels, detoxifies.

Muscle cells derive ATP from glycolytic conversion of glucose into lactate. Lactate is sent to the liver which is then converted to glucose.
What reactions are used to circumvent the pyruvate kinase reaction in gluconeogenesis? How many NTPs does the entire process require? Why?
Pyruvate carboxylase:
Pyruvate + CO2 + ATP + H2O-->Oxaloacetate + ADP + Pi + 2H+

Phophoenolpyruvate carboxykinase:
Oxaloacetate + GTP --> phosphoenolpyruvate + GDP + CO2

Two, deltaG of phosphoryl transfer = +62kJ/mol (2ATP-->100kJ/mol)
Why must malate to oxaloacetate in gluconeogenesis occur in cytosol?
OAA (produced in mito) is converted to malate and is transported across mitoch membrane into cytosol where it is then reduced to OAA. All the enzymes that react with OAA (for gluconeo) are in cytosol.
What reaction dose phosphofructokinase-1 catalyze?
Fructose-6P + ATP --> F-1,6-BP + ADP + H+
What reaction is used to circumvent PFK-1 in gluconeogenesis? Via what enzyme?
F-1,6-BP + H2O-->F-6P + Pi

Fructose 1,6 BPase
Why isn't gluconeogenesis the opposite of glycolysis?
The deltaG of glycolysis is negative, if it were in reverse, gluconeogenesis would have a huge deltaG to overcome. Wouldn't want that if we need efficient manufacture of glucose.
In the conversion of pyruvate to PEP in gluconeogensis, the addition of CO2 is followed by a decarboxylation. Why would nature add the CO2 only to remove it in the next step?

Is the carbon added the same as the one removed?
Decarboxylation releases energy that is coupled with the phosphorylation of OAA to PEP.

No. Carbon added was in mito, carbon removed in cytosol; have different chemical properties.
Consider the reaction from F-6P to F-1,6-BP in glycolysis and back again in gluconeogenesis.
Why are they said to be reciprocally regulated?

Why are they called a substrate/futile cycle?
Amounts and activities of the enzymes of each pathway are controlled so that both pathways aren’t highly active at the same time. High [AMP] indicates that energy charge is low and signals need for ATP generation.
PFK is inhibited by ATP/citrate--indicated biosynth precursors. AMP reverses this inhibitory action. Opposite for Fructose-1,6BPase

Small changes in rates of two opposing reactions result in a large change in the net flux of a product.
How does the small molecule F-2, 6-BP alter the activities of PFK-1 and F-1, 6 BPase?
Activator of PFK-1 by increasing its affinity for F-6P and diminishing the inhibitory effect of ATP. It shifts the conformational equilibrium from the T to the R state.
Will inhibit F-1,6-BPase.
Would epinephrine have the same effect as glucagon in the liver? Does the liver have epinephrine receptors? Glucagon receptors?
What effect would glucagon have in muscle? Does the muscle have glucagon receptors?
There are no glucagon receptors in muscle. Nor are there epinephrine receptors in the liver.
What effect would epinephrine have in muscle? Why?
Epinephrine would trigger a cAMP cascade and lead to phosphorylation of the bifunctional PFK2-FBPase2 enzyme by PKA.

Phosphorylation activates PFK-2 and inhibits F-2,6-BPase, increasing [F-2,6-BP]; thus increasing activity of PFK-1 (accelerating glycolysis) and inhibiting F-1,6,-BPase
Under what conditions is glucagon released? What are its effects?
When glucose is scarce, a rise in glucagon triggers cAMP cascade, leading to phosphorylation of bi enzyme by PKA. When glucose abundant, enzyme loses phosphate, which actiates PFK2 and inhibits FBPase2 (accelerating glycolysis in the end).
What happens in the cell as a result of a hormone signal?
Hormones affect gene expression primarily by changing the rate of transcription, as well as by regulating the degradation of mRNA.
What distinguishes metabolic control from hormonal control? AMP, ATP, and citrate are metabolic effectors whereas F-2,6-BP is produced primarily from a hormone signal.
Metabolic control is intrinsic: ATP and AMP are both produced and consumed by a metabolic pathways and the enzyme is able to respond to changes in the level of their substrates/products.
Hormonal control is more extrinsic: F-2,6,-BP is produced and consumed in response to a hormonal regulator (produced by PFK-2, and consumed by F-2,6-BPase). Phosphorylation by PKA (of a serine residue) is controlled by the alpha-s PKA pathway (under hormonal control).
It has been shown that muscle pyruvate kinase (PK) responds hyperbolically to its substrate, PEP, but the liver form of the enzyme responds sigmoidally. F-1,6,-BP is an allosteric activator of liver PK, but it apparently has no effect on the muscle enzyme.
Discuss why this regulation makes sense.
During times of moderate activity, muscles depend on anaerobic respiration, which calls for the conversion of pyruvate to lactate while releasing NAD+. Increases in PEP, and hence more glycolytic activity, would allow the muscle to produce more NAD+ to feed anaerobic respiration. The liver has to then convert this lactate to pyruvate and then into glucose…if you turned it all to pyruvate then you’d be promoting glycolysis and not gluconeogenesis.
What is the metabolic advantage of having the liver PK activated by F-1,6-BP?
Larger quantities of F-1,6-BP indicates that there is a large flow of incoming glycolytic intermediates, so PK must work faster to keep up with this flow.