Podcast
Questions and Answers
What is the primary function of gluconeogenesis in the body?
What is the primary function of gluconeogenesis in the body?
- To convert glucose into glycogen for storage.
- To maintain glucose levels during fasting. (correct)
- To break down fatty acids for energy.
- To enhance the uptake of glucose in muscle cells.
Which pathway requires energy input in the form of ATP?
Which pathway requires energy input in the form of ATP?
- Glycolysis.
- Cellular respiration.
- Lipolysis.
- Gluconeogenesis. (correct)
Which enzyme catalyzes the conversion of glucose-6-phosphate to glucose?
Which enzyme catalyzes the conversion of glucose-6-phosphate to glucose?
- Hexokinase.
- Pyruvate kinase.
- Glucose-6-phosphatase. (correct)
- Phospho-fructokinase.
Which of the following reactions is considered irreversible in glycolysis?
Which of the following reactions is considered irreversible in glycolysis?
In which organ does gluconeogenesis primarily occur?
In which organ does gluconeogenesis primarily occur?
Which reaction represents a bypass in gluconeogenesis?
Which reaction represents a bypass in gluconeogenesis?
What is the role of gluconeogenesis in fast-twitch muscle fibers?
What is the role of gluconeogenesis in fast-twitch muscle fibers?
Which organ contributes to gluconeogenesis under specific conditions, although to a lesser extent than the liver?
Which organ contributes to gluconeogenesis under specific conditions, although to a lesser extent than the liver?
What does Pyruvate Carboxylase catalyze in the process of gluconeogenesis?
What does Pyruvate Carboxylase catalyze in the process of gluconeogenesis?
What contributes to the spontaneity of the second reaction in the bypass of Pyruvate Kinase?
What contributes to the spontaneity of the second reaction in the bypass of Pyruvate Kinase?
What role does Acetyl CoA play in the activity of Pyruvate Carboxylase?
What role does Acetyl CoA play in the activity of Pyruvate Carboxylase?
What is the immediate product of the reaction catalyzed by PEP Carboxykinase?
What is the immediate product of the reaction catalyzed by PEP Carboxykinase?
How does an increase in oxaloacetate concentration affect the Krebs cycle?
How does an increase in oxaloacetate concentration affect the Krebs cycle?
What is a consequence of oxaloacetate depletion in the liver?
What is a consequence of oxaloacetate depletion in the liver?
What activates Pyruvate Carboxylase during gluconeogenesis?
What activates Pyruvate Carboxylase during gluconeogenesis?
In which metabolic pathway is oxaloacetate primarily utilized?
In which metabolic pathway is oxaloacetate primarily utilized?
What is produced as a byproduct of the conversion of oxaloacetate to PEP?
What is produced as a byproduct of the conversion of oxaloacetate to PEP?
Which statement best describes the energy contribution of ATP in gluconeogenesis?
Which statement best describes the energy contribution of ATP in gluconeogenesis?
What role does the subunit functioning as a translocase serve in relation to G-6-Pase?
What role does the subunit functioning as a translocase serve in relation to G-6-Pase?
Which of the following is the primary function of phosphofructokinase?
Which of the following is the primary function of phosphofructokinase?
What is required for bypassing the Pyruvate Kinase reaction?
What is required for bypassing the Pyruvate Kinase reaction?
What is the primary product of the reaction catalyzed by Fructose-1,6-bisphosphatase?
What is the primary product of the reaction catalyzed by Fructose-1,6-bisphosphatase?
Which statement correctly describes the relationship between PEP and ATP?
Which statement correctly describes the relationship between PEP and ATP?
In glycolysis, what is the substrate that phosphofructokinase acts on?
In glycolysis, what is the substrate that phosphofructokinase acts on?
What is the process of gluconeogenesis primarily aimed at producing?
What is the process of gluconeogenesis primarily aimed at producing?
Which of the following statements about ATP is true in the context of glycolysis?
Which of the following statements about ATP is true in the context of glycolysis?
What is the result of hydrolyzing one phosphate bond from ATP during the conversion of PEP?
What is the result of hydrolyzing one phosphate bond from ATP during the conversion of PEP?
What is the end product of the reaction catalyzed by pyruvate kinase in glycolysis?
What is the end product of the reaction catalyzed by pyruvate kinase in glycolysis?
What is the primary role of fructose-2,6-bisphosphate in the metabolic pathways discussed?
What is the primary role of fructose-2,6-bisphosphate in the metabolic pathways discussed?
How does ATP influence the regulation of glycolysis and gluconeogenesis?
How does ATP influence the regulation of glycolysis and gluconeogenesis?
What is the significance of the reciprocal allosteric regulation by adenine nucleotides?
What is the significance of the reciprocal allosteric regulation by adenine nucleotides?
Which of the following best describes the action of Protein Kinase A (PKA) on metabolic pathways?
Which of the following best describes the action of Protein Kinase A (PKA) on metabolic pathways?
What is the effect of glucagon on liver cells in terms of metabolic control?
What is the effect of glucagon on liver cells in terms of metabolic control?
What is the primary source of pyruvate and oxaloacetate for gluconeogenesis during fasting?
What is the primary source of pyruvate and oxaloacetate for gluconeogenesis during fasting?
Which of the following enzymes converts oxaloacetate to phosphoenolpyruvate in gluconeogenesis?
Which of the following enzymes converts oxaloacetate to phosphoenolpyruvate in gluconeogenesis?
How many ATP equivalents are expended in the process of gluconeogenesis?
How many ATP equivalents are expended in the process of gluconeogenesis?
What molecule derived from fat cells contributes significantly to gluconeogenesis?
What molecule derived from fat cells contributes significantly to gluconeogenesis?
Which of the following statements about glycolysis and gluconeogenesis is TRUE?
Which of the following statements about glycolysis and gluconeogenesis is TRUE?
What is the end product of gluconeogenesis?
What is the end product of gluconeogenesis?
Which enzyme is responsible for the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate?
Which enzyme is responsible for the conversion of fructose-1,6-bisphosphate to fructose-6-phosphate?
What would occur if glycolysis and gluconeogenesis were both active in a cell?
What would occur if glycolysis and gluconeogenesis were both active in a cell?
Which of the following is NOT a precursor for gluconeogenesis?
Which of the following is NOT a precursor for gluconeogenesis?
What is the primary function of pyruvate carboxylase in gluconeogenesis?
What is the primary function of pyruvate carboxylase in gluconeogenesis?
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Study Notes
Gluconeogenesis Overview
- Gluconeogenesis converts lactate to glucose, utilizing some glycolytic reactions in reverse and unique reactions specific to this pathway.
- Requires ATP input to maintain blood glucose levels during fasting and provides glucose to fast-twitch muscle fibers.
- Primarily occurs in the liver, with limited activity in the kidneys and small intestine under certain conditions.
Enzyme Pathways
- Many gluconeogenesis enzymes overlap with glycolysis, except three critical glycolytic enzymes:
- Hexokinase/Glucokinase
- Phosphofructokinase
- Pyruvate Kinase
- These enzymes facilitate irreversible reactions that must be bypassed in gluconeogenesis.
Bypass Reactions
- Hexokinase/Glycolysis Reaction:
- Catalyzes glucose + ATP to glucose-6-phosphate + ADP.
- Fructose-1,6-bisphosphatase/Gluconeogenesis Reaction:
- Converts fructose-1,6-bisphosphate + H2O to fructose-6-phosphate + Pi.
- Bypassing Pyruvate Kinase involves two steps:
- Pyruvate Carboxylase: Pyruvate + HCO3- + ATP → Oxaloacetate + ADP + Pi.
- PEP Carboxykinase: Oxaloacetate + GTP → PEP + GDP + CO2.
Role of Acetyl CoA
- Pyruvate Carboxylase is allosterically activated by acetyl CoA.
- The demand for oxaloacetate increases during gluconeogenesis, potentially limiting the Krebs cycle.
Substrate Sources for Gluconeogenesis
- Predominantly derived from amino acid catabolism during fasting or starvation.
- Muscle protein degradation supplies amino acids for conversion to gluconeogenesis substrates.
- Glycerol, from fat breakdown, contributes significantly to gluconeogenesis.
Reciprocal Regulation of Pathways
- Glycolysis and gluconeogenesis are reciprocally regulated to prevent futile cycles:
- Phosphofructokinase is inhibited by ATP, stimulated by AMP.
- Fructose-1,6-bisphosphatase is inhibited by AMP.
- High ATP promotes glucose storage as glycogen, while low ATP levels stimulate gluconeogenesis.
Global Control in Liver Cells
- Low blood glucose levels trigger glucagon release, activating a cyclic AMP cascade.
- Protein Kinase A is responsible for phosphorylating and inhibiting glycolysis while stimulating gluconeogenesis.
- Fructose-2,6-bisphosphate regulates both pathways, enhancing glycolysis while inhibiting gluconeogenesis.
Key Energy Costs
- Glycolysis generally yields 2 ATP per glucose molecule processed.
- Gluconeogenesis expends 6 ATP equivalents to synthesize glucose.
- A futile cycle of simultaneous glycolysis and gluconeogenesis would waste 4 ATP.
Summary of Glycolysis and Gluconeogenesis
- Glycolysis Reaction:
- Glucose + 2 NAD+ + 2 ADP + 2 Pi → 2 Pyruvate + 2 NADH + 2 ATP.
- Gluconeogenesis Reaction:
- 2 Pyruvate + 2 NADH + 4 ATP + 2 GTP → Glucose + 2 NAD+ + 4 ADP + 2 GDP + 6 Pi.
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