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ppt 14 Biochem
| Question | Answer |
|---|---|
| What is the primary definition and location of gluconeogenesis? | The synthesis of glucose from non-carbohydrate precursors, occurring mainly in the liver and kidney. |
| Which of the following is NOT a major substrate precursor for gluconeogenesis? | Fatty acids |
| Gluconeogenesis is largely the reverse of glycolysis, but it uses four unique enzymes to bypass irreversible glycolytic steps. Which of the following is one of these unique enzymes? | Pyruvate carboxylase |
| The conversion of pyruvate to phosphoenolpyruvate (PEP) is a two-step process in gluconeogenesis. What are the two enzymes that catalyze these steps? | Pyruvate carboxylase and Phosphoenolpyruvate carboxykinase (PEPCK) |
| The enzyme pyruvate carboxylase uses a covalently attached cofactor to carry out its catalytic function. What is this cofactor? | Biotin |
| Fructose-2,6-bisphosphate (F2,6P) is a key regulator that prevents a futile cycle between glycolysis and gluconeogenesis. How does it function? | It activates phosphofructokinase-1 (PFK-1) and inhibits fructose 1,6-bisphosphatase (FBPase). |
| The hormone glucagon stimulates gluconeogenesis. What is the direct effect of the glucagon-initiated signaling cascade on the bifunctional enzyme PFK-2/FBPase-2? | Protein Kinase A phosphorylates the enzyme, activating the FBPase-2 domain and inactivating the PFK-2 domain. |
| Why would the simultaneous, unregulated operation of glycolysis and gluconeogenesis be considered a 'futile cycle'? | There would be a net consumption of high-energy phosphate bonds (ATP and GTP) with no net metabolic work done. |
| The final reaction of gluconeogenesis, which makes free glucose available for transport out of the cell, is catalyzed by which enzyme? | Glucose 6-phosphatase |
| Under which physiological condition is the rate of gluconeogenesis expected to be highest? | During a period of fasting or starvation. |
| According to the provided diagram, which two amino acids are exceptions to the rule that most amino acids are glucogenic? | Leucine and Lysine |
| The conversion of pyruvate to phosphoenolpyruvate bypasses an irreversible step in glycolysis. What is the net cost in high-energy phosphate bonds for this two-step conversion per molecule of pyruvate? | One ATP and one GTP |
| The material states that pyruvate carboxylase uses biotin as a cofactor. How is this biotin molecule associated with the enzyme? | It is covalently attached to a Lysine residue |
| Glycerol, a precursor for gluconeogenesis, is derived from the breakdown of triacylglycerols (TAGs). At what point does it enter the gluconeogenic pathway? | As a triose phosphate |
| The hormone glucagon stimulates gluconeogenesis. What is the direct enzymatic action of Protein Kinase A (PKA) in this signaling pathway? | It phosphorylates the PFK-2/FBPase-2 bifunctional enzyme |
| Phosphorylation of the bifunctional enzyme PFK-2/FBPase-2 has opposing effects on its two domains. What is the result of this phosphorylation? | The FBPase-2 activity is activated, and the PFK-2 activity is inactivated |
| The reactions catalyzed by fructose-1,6-bisphosphatase and glucose-6-phosphatase are critical, irreversible steps in gluconeogenesis. What type of chemical reaction do they both perform? | Hydrolysis |
| During a fasting state, the concentration of fructose-2,6-bisphosphate (F2,6BP) decreases. What is the immediate consequence of this change for the gluconeogenic pathway? | The inhibition of fructose-1,6-bisphosphatase is relieved |
| In the hormonal regulation of gluconeogenesis by glucagon, which molecule functions as the second messenger that directly activates Protein Kinase A? | Cyclic AMP (cAMP) |
| Lactate, produced in tissues like exercising muscle, is a major substrate for gluconeogenesis in the liver. What is the first molecule it is converted into to enter the pathway? | Pyruvate |
| Gluconeogenesis is metabolically expensive. What is the total cost in high-energy phosphate bonds (ATP + GTP) to synthesize one molecule of glucose from two molecules of pyruvate? | Six (4 ATP and 2 GTP) |
| While four enzymes are unique to gluconeogenesis, many are shared with glycolysis. Which of these enzymes catalyzes a reaction in both pathways? | Aldolase |
| The synthesis of glucose is particularly vital during fasting to supply fuel for which specific types of cells mentioned in the text? | Central Nervous System (CNS) and Red Blood Cells (RBCs) |
| The reciprocal regulation by fructose-2,6-bisphosphate (F2,6P) is crucial. While it inhibits gluconeogenesis, it simultaneously stimulates glycolysis by activating which enzyme? | Phosphofructokinase-1 (PFK-1) |
| The final step of gluconeogenesis in the liver is the dephosphorylation of glucose-6-phosphate. What are the two products of this reaction catalyzed by glucose-6-phosphatase? | Glucose and inorganic phosphate (HPO |
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