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What is the primary enzyme responsible for the phosphorylation of fructose?
In which organ does the majority of fructose metabolism occur?
What is the product of the cleavage of fructose-1-phosphate?
Which of the following statements describes fructokinase?
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What condition arises from a deficiency of fructokinase?
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What intermediate does DHAP represent in fructose metabolism?
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Which enzyme cleaves fructose-1-phosphate into its components?
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Which of the following tissues contains hexokinase for fructose conversion?
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Which inherited disorder is characterized by hereditary fructose intolerance?
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What is the primary metabolic state known as when fasting lasts longer than 12 hours?
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Which hormones primarily regulate glucose production during fasting?
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What happens to glycogenolysis after 15 hours of fasting?
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What substrates are key for gluconeogenesis as fasting continues?
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During the fed state, what is the primary function of insulin?
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Which of the following statements about sucrase is incorrect?
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What is the process that phosphorylates glyceraldehyde?
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Which product is formed from the phosphorylation of glyceraldehyde?
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What can glyceraldehyde-3-phosphate be further converted to?
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Which enzyme cleaves fructose-1-phosphate?
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What intermediate is produced from dihydroxyacetone phosphate?
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Which metabolic pathway can glyceraldehyde-3-phosphate NOT directly enter?
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What type of substrate is glyceraldehyde in this metabolic process?
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Which of the following describes a path for glyceraldehyde metabolism?
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What is the starting substrate for the phosphorylation process in fructose metabolism?
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Which product can glyceraldehyde-3-phosphate be converted into through gluconeogenesis?
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What is the role of fructose 1,6 bisphosphate in glycolysis?
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Which molecule is produced during the payoff phase of glycolysis?
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What hormone induces the activity of 1,6-bisphosphatase in the fed state of adipose tissues?
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What regulates PFK-1 activity in glycolysis?
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What process primarily provides energy to erythrocytes given they lack mitochondria?
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Which enzyme is induced by glucagon, epinephrine, and cortisol during fasting?
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Substrate-level phosphorylation occurs in which phase of glycolysis?
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What stimulates the activity of PFK-1?
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What is the consequence of insulin acting on the PEPCK enzyme?
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What happens when the cell has an ample supply of ATP?
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Which statement about glucose entry into red blood cells is accurate?
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Which process is NOT a characteristic of the fed state in the brain?
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How many molecules of G3P are involved in the reactions from step 6 to step 10 of glycolysis?
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Which factor does NOT inhibit PFK-1?
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What is the main fate of fatty acids taken up by cells in the fed state?
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Fructose 2,6-bisphosphatase activity is activated when it is:
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Which process occurs during substrate-level phosphorylation?
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In terms of energy gain, what is the primary mechanism during the payoff phase of glycolysis?
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During fasting, what effect does glucagon have on glycolysis in the liver?
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What does pyruvate convert to after glycolysis in red blood cells?
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Study Notes
Fructose Metabolism
- Fructose is the second most common sugar in the adult diet
- Primarily ingested as a monosaccharide or as part of sucrose
- Found in fruits, honey, and corn syrups
- Mostly metabolized in the liver
- Also metabolized in the small intestinal mucosa and proximal epithelium of the renal tubule
Fructose Metabolism Enzymes
- Fructokinase is the major kinase involved in fructose metabolism
- Fructokinase has a high Vmax and is found in the liver
- Hexokinase (I, II, III) are also involved in fructose metabolism
- Hexokinase has a high Vmax and is found in muscle and adipose tissue
- Hexokinase converts fructose to fructose-6-phosphate
Fructose-1-Phosphate Cleavage
- Fructose-1-phosphate is cleaved into dihydroxyacetone phosphate (DHAP) and glyceraldehyde by aldolase-B
- DHAP is a glycolytic intermediate
- Glyceraldehyde can be converted to glyceraldehyde-3-phosphate (G3P) by triose kinase
Fructose Metabolism Summary
- Fructose is phosphorylated to fructose-1-phosphate by fructokinase
- Fructose-1-phosphate is cleaved into DHAP and glyceraldehyde by aldolase-B
- DHAP can enter the glycolytic pathway directly
- Glyceraldehyde can be converted to G3P, which can also enter the glycolytic pathway
Inherited Disorders of Fructose Metabolism
- Essential fructosuria is caused by a deficiency in fructokinase
- Hereditary fructose intolerance is caused by a deficiency in aldolase-B
Fed State vs Fasting State
- Fed state (postprandial) occurs within 4 hours after a meal
- Insulin stimulates glucose uptake and metabolism
- Insulin promotes glycolysis and glycogenesis
- Fasting state (post-absorptive) occurs after 6-12 hours of fasting
- Prolonged fasting (starvation) occurs after more than 12 hours of fasting
- Glucagon stimulates gluconeogenesis and glycogenolysis
- Glucagon inhibits glycolysis and glycogenesis
Gluconeogenesis
- The liver switches from glucose utilization to glucose production during fasting
- The key substrates for gluconeogenesis are alanine, lactate, and glycerol
- Alanine and lactate are transported to the liver from muscle
- Glycerol is released from the hydrolysis of triacylglycerols (lipolysis) by the hormone-sensitive lipase, which is stimulated by glucagon
- Gluconeogenesis increases with duration of fasting
Glycogenolysis
- After 15 hours of fasting, glycogenolysis occurs to maintain blood sugar levels
Sucrose Hydrolysis
- Sucrase hydrolyzes the α1→B2 glycosidic bond of sucrose to form glucose and fructose
- Sucrose is a non-reducing sugar
- Sucrose is not formed by an α1→1 glycosidic bond, this applies to trehalose
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Description
Explore the complexities of fructose metabolism, including its enzymatic pathways and roles in the human body. Learn about key enzymes like fructokinase and hexokinase and their importance in converting fructose into usable energy. This quiz will test your understanding of fructose's metabolism and its implications for health.
