Podcast
Questions and Answers
What is the effect of increased glucagon secretion on fructose-2,6-bisphosphate levels?
What is the effect of increased glucagon secretion on fructose-2,6-bisphosphate levels?
- It causes a fluctuating effect on fructose-2,6-bisphosphate levels.
- It increases fructose-2,6-bisphosphate levels.
- It has no effect on fructose-2,6-bisphosphate levels.
- It decreases fructose-2,6-bisphosphate levels. (correct)
How does low blood glucose affect glycolysis and gluconeogenesis?
How does low blood glucose affect glycolysis and gluconeogenesis?
- Glycolysis and gluconeogenesis both remain unchanged.
- Both glycolysis and gluconeogenesis are inhibited.
- Glycolysis is accelerated while gluconeogenesis is inhibited.
- Glycolysis slows down and gluconeogenesis is accelerated. (correct)
What is the role of protein kinase A in response to low blood glucose?
What is the role of protein kinase A in response to low blood glucose?
- It phosphorylates enzymes involved in glycolysis and gluconeogenesis. (correct)
- It inactivates all metabolic processes.
- It decreases cAMP levels, reducing enzyme activity.
- It enhances glycolysis by activating PFK.
What happens to glycogen metabolism when blood glucose levels are low?
What happens to glycogen metabolism when blood glucose levels are low?
In muscle tissue, what differentiates its control mechanism for fructose-2,6-bisphosphate?
In muscle tissue, what differentiates its control mechanism for fructose-2,6-bisphosphate?
What is the first step in the bypass of the pyruvate kinase reaction during gluconeogenesis?
What is the first step in the bypass of the pyruvate kinase reaction during gluconeogenesis?
Which enzyme is responsible for converting fructose-1,6-bisphosphate to fructose-6-phosphate?
Which enzyme is responsible for converting fructose-1,6-bisphosphate to fructose-6-phosphate?
Which reaction is not directly reversible during gluconeogenesis?
Which reaction is not directly reversible during gluconeogenesis?
What role does biotin play in gluconeogenesis?
What role does biotin play in gluconeogenesis?
During low blood glucose levels, which hormone's increased secretion affects gluconeogenesis?
During low blood glucose levels, which hormone's increased secretion affects gluconeogenesis?
Which tissue is primarily responsible for gluconeogenesis?
Which tissue is primarily responsible for gluconeogenesis?
What is the role of fructose-2,6-bisphosphate during gluconeogenesis?
What is the role of fructose-2,6-bisphosphate during gluconeogenesis?
Which step in gluconeogenesis specifically requires GTP?
Which step in gluconeogenesis specifically requires GTP?
What is the effect of increased insulin secretion during high blood glucose?
What is the effect of increased insulin secretion during high blood glucose?
How does fructose-2,6-bisphosphate affect gluconeogenesis?
How does fructose-2,6-bisphosphate affect gluconeogenesis?
Which enzyme is inhibited by ATP and citrate as allosteric inhibitors?
Which enzyme is inhibited by ATP and citrate as allosteric inhibitors?
What role do glucagon and adrenaline play in the regulation of glycogen metabolism?
What role do glucagon and adrenaline play in the regulation of glycogen metabolism?
Which statement correctly describes the effect of AMP on PFK and FBPase activities?
Which statement correctly describes the effect of AMP on PFK and FBPase activities?
What is one of the key products of the pentose phosphate pathway when using 3x glucose-6-phosphate?
What is one of the key products of the pentose phosphate pathway when using 3x glucose-6-phosphate?
Which phase is NOT part of the pentose phosphate pathway?
Which phase is NOT part of the pentose phosphate pathway?
Which type of tissues primarily utilize the pentose phosphate pathway?
Which type of tissues primarily utilize the pentose phosphate pathway?
What substance does NADPH help reduce to eliminate Reactive Oxygen Species (ROS)?
What substance does NADPH help reduce to eliminate Reactive Oxygen Species (ROS)?
What common misconception is associated with the pentose phosphate pathway?
What common misconception is associated with the pentose phosphate pathway?
During the oxidative phase of the pentose phosphate pathway, how many carbon atoms are released as CO2?
During the oxidative phase of the pentose phosphate pathway, how many carbon atoms are released as CO2?
What is the primary importance of producing NADPH in the pentose phosphate pathway?
What is the primary importance of producing NADPH in the pentose phosphate pathway?
In the non-oxidative stage of the pentose phosphate pathway, which compound is produced along with two molecules of fructose-6-phosphate?
In the non-oxidative stage of the pentose phosphate pathway, which compound is produced along with two molecules of fructose-6-phosphate?
What enzyme catalyzes the phosphorylation of fructose in the major metabolic pathway in the liver?
What enzyme catalyzes the phosphorylation of fructose in the major metabolic pathway in the liver?
What is the product of the cleavage of fructose 1-phosphate by aldolase B?
What is the product of the cleavage of fructose 1-phosphate by aldolase B?
What metabolic defect leads to fructose (sucrose) intolerance in newborns?
What metabolic defect leads to fructose (sucrose) intolerance in newborns?
What condition is caused by the accumulation of fructose-1-phosphate in the liver?
What condition is caused by the accumulation of fructose-1-phosphate in the liver?
Which metabolic pathway do red blood cells primarily rely on for ATP generation?
Which metabolic pathway do red blood cells primarily rely on for ATP generation?
What metabolite produced in red blood cells modulates hemoglobin's oxygen affinity?
What metabolite produced in red blood cells modulates hemoglobin's oxygen affinity?
Which enzyme is inhibited by high concentrations of fructose-1-phosphate affecting ATP generation?
Which enzyme is inhibited by high concentrations of fructose-1-phosphate affecting ATP generation?
Approximately what percentage of glucose in red blood cells is used to produce 2,3-bisphosphoglycerate?
Approximately what percentage of glucose in red blood cells is used to produce 2,3-bisphosphoglycerate?
What is a key function of NADPH generated from the oxidative branch of the pentose phosphate pathway in red blood cells?
What is a key function of NADPH generated from the oxidative branch of the pentose phosphate pathway in red blood cells?
Which enzyme directly converts 1,3-bisphosphoglycerate (1,3-BPG) into 2,3-bisphosphoglycerate (2,3-BPG)?
Which enzyme directly converts 1,3-bisphosphoglycerate (1,3-BPG) into 2,3-bisphosphoglycerate (2,3-BPG)?
Flashcards
Fructose metabolism
Fructose metabolism
A minor metabolic pathway where fructose is converted to fructose-1-phosphate, then further metabolized.
Fructokinase
Fructokinase
Enzyme that phosphorylates fructose to fructose-1-phosphate in liver, kidney, and intestine.
Fructose 1-phosphate
Fructose 1-phosphate
Intermediate in fructose metabolism, split by Aldolase B.
Aldolase B
Aldolase B
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Fructose intolerance
Fructose intolerance
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2,3-BPG
2,3-BPG
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Glycolysis in RBCs
Glycolysis in RBCs
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Pentose Phosphate Pathway (PPP)
Pentose Phosphate Pathway (PPP)
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NADPH
NADPH
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Glycogenolysis
Glycogenolysis
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Gluconeogenesis
Gluconeogenesis
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Pyruvate Carboxylase
Pyruvate Carboxylase
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PEPCK
PEPCK
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Fructose Bisphosphatase
Fructose Bisphosphatase
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Glucose-6-phosphatase
Glucose-6-phosphatase
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Regulation of gluconeogenesis
Regulation of gluconeogenesis
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Glycogenesis
Glycogenesis
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Glycogen phosphorylase
Glycogen phosphorylase
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Oxidative phase of PPP
Oxidative phase of PPP
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Non-oxidative phase of PPP
Non-oxidative phase of PPP
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Study Notes
Fructose Metabolism
- Enzyme hexokinase shows low affinity for fructose, making this a minor metabolic pathway.
- In the liver, fructokinase phosphorylates fructose to fructose 1-phosphate; this enzyme is also present in the kidney and intestine.
- Fructose 1-phosphate is split by aldolase B into glyceraldehyde and dihydroxyacetone phosphate (DHAP).
Fructose Intolerance
- Fructose intolerance arises from a defect involving fructose-1-phosphate aldolase B, leading to accumulation of fructose-1-phosphate in the liver.
- Accumulation causes liver damage and jaundice.
- High fructose-1-phosphate levels inhibit aldolase in glycolysis and glycogen phosphorylase, resulting in reduced ATP generation and hypoglycemia.
Glycolysis and Red Blood Cells (RBCs)
- RBCs exclusively depend on glycolysis for ATP production.
- Around 25% of glucose utilized in RBCs generates 2,3-bisphosphoglycerate (2,3-BPG), crucial for modulating hemoglobin's oxygen affinity.
- RBCs utilize the oxidative branch of the pentose phosphate pathway (PPP) to synthesize NADPH, maintaining glutathione homeostasis against oxidative stress.
Importance of Glycolysis in RBCs
- Glycolysis produces 2,3-BPG, an allosteric effector that facilitates oxygen release from hemoglobin.
Pentose Phosphate Pathway (PPP)
- Comprises three phases: Oxidation, Isomerization, and Sugar rearrangement.
- Utilizing three glucose-6-phosphate yields:
- 3 CO2
- 6 NADPH
- 2 Fructose-6-phosphate
- Glyceraldehyde
- Active in tissues synthesizing fatty acids or sterols where NADPH is required; lower activity observed in muscle and brain.
Carbon Pathway in PPP
- In oxidative phase, three six-carbon molecules convert to three five-carbon sugars, releasing three CO2.
- In non-oxidative phase, three five-carbon sugars rearrange to form two six-carbon sugars and one three-carbon compound.
Importance of NADPH
- NADPH maintains protein thiol groups in a reduced state and reduces oxidized glutathione.
- Reduced glutathione detoxifies reactive oxygen species (ROS), preventing membrane damage and hemoglobin alteration from peroxides.
Glycogenolysis
- Glycogen phosphorylase cleaves α(1-6) glycosidic bonds during degeneration of glycogen.
Gluconeogenesis
- Gluconeogenesis synthesizes glucose from precursors like pyruvate, lactate, and amino acids; it bypasses irreversible glycolytic reactions.
- Bypass steps involve:
- Carboxylation of pyruvate to oxaloacetate (catalyzed by pyruvate carboxylase).
- Conversion of oxaloacetate to phosphoenolpyruvate by phosphoenolpyruvate carboxykinase (PEPCK).
- Fructose-1,6-bisphosphate being converted to fructose-6-phosphate by fructose bisphosphatase.
- Glucose-6-phosphate converted to glucose by glucose-6-phosphatase, unique to liver and kidney.
Regulation of Gluconeogenesis
- Low blood glucose triggers glucagon secretion, enhancing enzyme phosphorylation.
- Increases concentration of fructose-2,6-bisphosphate leads to:
- Inhibition of glycolytic phosphofructokinase-1 (PFK).
- Activation of fructose-1,6-bisphosphatase, promoting gluconeogenesis.
- High blood glucose enhances insulin secretion, leading to enzyme dephosphorylation, activating PFK and inhibiting fructose-2,6-bisphosphatase, stimulating glycolysis.
Control of Glycogenesis and Glycogenolysis
- Reciprocal regulation of glycogen synthesis and breakdown occurs via phosphorylation and dephosphorylation.
- Hormonal regulation by glucagon and adrenalin promotes phosphorylation, while insulin promotes dephosphorylation of glycogen synthase and phosphorylase.
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Description
This quiz explores the metabolism of fructose, focusing on the role of the enzyme fructokinase in the liver, kidney, and intestine. It also highlights the differences in phosphorylating fructose versus glucose. Test your knowledge on these metabolic pathways and enzyme affinities.
