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Which of the following sugars are important in vertebrates?
Which of the following sugars are important in vertebrates?
Besides glucose, what are the most common sugars found in oligosaccharides and polysaccharides?
Besides glucose, what are the most common sugars found in oligosaccharides and polysaccharides?
Fructose, galactose, and mannose.
Fructose is converted to fructose-1-phosphate by fructokinase.
Fructose is converted to fructose-1-phosphate by fructokinase.
True
Fructose-1-phosphate is split into ______ and glyceraldehyde by fructose-1-phosphate aldolase.
Fructose-1-phosphate is split into ______ and glyceraldehyde by fructose-1-phosphate aldolase.
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Fructose-1-phosphate enters the glycolytic pathway directly.
Fructose-1-phosphate enters the glycolytic pathway directly.
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The conversion of fructose-1-phosphate into glycolytic intermediates bypasses two regulatory steps.
The conversion of fructose-1-phosphate into glycolytic intermediates bypasses two regulatory steps.
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What metabolic disorder is caused by a deficiency of fructokinase?
What metabolic disorder is caused by a deficiency of fructokinase?
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Hereditary fructose intolerance is caused by a deficiency of fructose-1-P-aldolase.
Hereditary fructose intolerance is caused by a deficiency of fructose-1-P-aldolase.
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What is the primary function of galactokinase?
What is the primary function of galactokinase?
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The hereditary disorder galactosemia is caused by the absence of galactose-1-phosphate uridyltransferase.
The hereditary disorder galactosemia is caused by the absence of galactose-1-phosphate uridyltransferase.
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UDP-glucose is formed by the isomerization of UDP-galactose.
UDP-glucose is formed by the isomerization of UDP-galactose.
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UDP-glucose can be used directly in glycogen synthesis or converted to glucose-1-phosphate.
UDP-glucose can be used directly in glycogen synthesis or converted to glucose-1-phosphate.
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What is the primary cause of galactosemia?
What is the primary cause of galactosemia?
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What is the most effective treatment for galactosemia?
What is the most effective treatment for galactosemia?
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The citric acid cycle is a series of biochemical reactions used by aerobic organisms.
The citric acid cycle is a series of biochemical reactions used by aerobic organisms.
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What is the primary function of the citric acid cycle?
What is the primary function of the citric acid cycle?
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Acetyl-CoA is synthesized from pyruvate in a series of reactions.
Acetyl-CoA is synthesized from pyruvate in a series of reactions.
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What are the two products formed when carbon atoms are oxidized in the citric acid cycle?
What are the two products formed when carbon atoms are oxidized in the citric acid cycle?
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The citric acid cycle produces ______ NADH, ______ FADH2, and one GTP.
The citric acid cycle produces ______ NADH, ______ FADH2, and one GTP.
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The net reaction of the citric acid cycle is reversible.
The net reaction of the citric acid cycle is reversible.
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What is the name of the complex that catalyzes the conversion of pyruvate to acetyl CoA?
What is the name of the complex that catalyzes the conversion of pyruvate to acetyl CoA?
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The pyruvate dehydrogenase complex requires five coenzymes.
The pyruvate dehydrogenase complex requires five coenzymes.
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One molecule of NADH is produced for each molecule of pyruvate converted to acetyl-CoA.
One molecule of NADH is produced for each molecule of pyruvate converted to acetyl-CoA.
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The citric acid cycle is a catabolic process only.
The citric acid cycle is a catabolic process only.
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Anabolic processes can drain the citric acid cycle of its intermediates.
Anabolic processes can drain the citric acid cycle of its intermediates.
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What type of reactions replenish the citric acid cycle intermediates?
What type of reactions replenish the citric acid cycle intermediates?
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Pyruvate carboxylase is activated by high concentrations of acetyl-CoA.
Pyruvate carboxylase is activated by high concentrations of acetyl-CoA.
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Pyruvate carboxylase deficiency is characterized by varying degrees of mental retardation.
Pyruvate carboxylase deficiency is characterized by varying degrees of mental retardation.
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A prominent symptom of pyruvate carboxylase deficiency is lactic aciduria.
A prominent symptom of pyruvate carboxylase deficiency is lactic aciduria.
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What are the three key enzymes regulated in the citric acid cycle?
What are the three key enzymes regulated in the citric acid cycle?
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High concentrations of succinyl-CoA and citrate stimulate citrate synthase activity.
High concentrations of succinyl-CoA and citrate stimulate citrate synthase activity.
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Isocitrate dehydrogenase is stimulated by high concentrations of ADP and NAD+.
Isocitrate dehydrogenase is stimulated by high concentrations of ADP and NAD+.
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A-ketoglutarate dehydrogenase is strictly regulated due to its importance in several metabolic processes.
A-ketoglutarate dehydrogenase is strictly regulated due to its importance in several metabolic processes.
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When a cell's energy stores are low, a-ketoglutarate dehydrogenase is inhibited.
When a cell's energy stores are low, a-ketoglutarate dehydrogenase is inhibited.
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As the cell's supply of NADH rises, a-ketoglutarate dehydrogenase activity is stimulated.
As the cell's supply of NADH rises, a-ketoglutarate dehydrogenase activity is stimulated.
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Study Notes
Metabolism of Other Monosaccharides
- Several sugars besides glucose are crucial in vertebrates, including fructose, galactose, and mannose.
- These sugars are common components of oligosaccharides and polysaccharides.
- They serve as energy sources, converted into glycolytic intermediates.
Fructose Metabolism
- Dietary fructose sources include fruit, honey, and sucrose.
- Fructose is a significant carbohydrate source, second only to glucose.
- In the liver, fructose is converted to fructose-1-phosphate by fructokinase.
- Before entering the glycolytic pathway, fructose-1-phosphate is split into dihydroxyacetone phosphate (DHAP) and glyceraldehyde by fructose-1-phosphate aldolase (aldolase-B).
- DHAP is then converted to glyceraldehyde-3-phosphate by triose phosphate isomerase.
- Fructose metabolism bypasses two regulatory steps (hexokinase and PFK-1), making it metabolized faster than glucose.
Hereditary Fructose Intolerance
- An inherited metabolic disorder due to fructose-1-P-aldolase (aldolase-B) deficiency.
- Accumulation of fructose-1-phosphate inhibits glycogen phosphorylase, leading to fasting hypoglycemia, especially after fructose ingestion.
Galactose Metabolism
- Galactose, despite similar structure to glucose (C4 epimers), requires specific reactions to enter the glycolytic pathway.
- Galactose is initially converted to galactose-1-phosphate by galactokinase.
- Galactose-1-phosphate is transformed into UDP-galactose during fetal/childhood development by galactose-1-phosphate uridyltransferase.
- Galactosemia is a genetic disorder caused by the absence of this enzyme.
- UDP-glucose is formed through the isomerization of UDP-galactose, catalyzed by UDP-galactose-4-epimerase.
- UDP-glucose is used in glycogen synthesis or converted to glucose-1-phosphate by UDP-glucose pyrophosphorylase.
- Glucose-1-phosphate enters the glycolytic pathway after conversion to glucose-6-phosphate by phosphoglucomutase.
Galactosemia
- Caused by the absence of galactose-1-phosphate uridyltransferase.
- Leads to accumulation of galactose, galactose-1-phosphate, and galactitol, causing liver damage, cataracts, and mental retardation.
- Early diagnosis and a galactose-free diet are vital for treatment.
Citric Acid Cycle
- A series of biochemical reactions in aerobic organisms releasing chemical energy from acetyl-CoA.
- Derived from the breakdown of carbohydrates, lipids, and amino acids.
- Acetyl-CoA is synthesized from pyruvate.
- Carbon atoms are oxidized to CO2, with high-energy electrons transferred to NAD+ and FAD.
- Produces reduced coenzymes NADH and FADH2.
Conversion of Pyruvate to Acetyl CoA
- Pyruvate is converted to acetyl CoA after transport into the mitochondrial matrix in a series of reactions. Catalyzed by the pyruvate dehydrogenase complex comprised of three enzyme activities.
- This complex requires five coenzymes (TPP, lipoic acid, NAD+, FAD, CoASH).
- One molecule of NADH is produced per pyruvate molecule converted to acetyl-CoA.
Citric Acid Cycle Reactions
- Introduction of two carbons: Acetyl-CoA condenses with oxaloacetate forming citrate, catalyzed by citrate synthase.
- Isomerization: Citrate is isomerized to isocitrate by aconitase.
- Oxidation of isocitrate: Isocitrate is oxidized to α-ketoglutarate, producing the first NADH and CO2; catalyzed by isocitrate dehydrogenase.
- Oxidation of α-ketoglutarate: α-ketoglutarate is oxidized to succinyl-CoA, producing the second NADH and CO2; catalyzed by α-ketoglutarate dehydrogenase complex requiring five coenzymes.
- Cleavage of succinyl-CoA: Succinyl-CoA is cleaved to succinate, with GTP production from GDP catalyzed by succinate thiokinase.
- Oxidation of succinate: Succinate is oxidized to fumarate by succinate dehydrogenase, producing FADH2.
- Hydration of fumarate: Fumarate is hydrated to L-malate by fumarase.
- Oxidation of malate: Malate is oxidized to oxaloacetate, producing the third NADH, catalyzed by malate dehydrogenase.
Citric Acid Cycle Regulation
- Citrate synthase, isocitrate dehydrogenase, and α-ketoglutarate dehydrogenase are key regulatory enzymes in the citric acid cycle.
- These enzymes are stimulated/inhibited by metabolic indicators like acetyl-CoA, oxaloacetate, succinyl-CoA, citrate, ATP, ADP, and NAD+, and NADH.
Pyruvate Carboxylase Deficiency
- A fatal disease due to a missing or defective pyruvate carboxylase.
- Characterized by mental retardation, metabolic disturbances in amino acid pathways, and lactic aciduria.
Amphibolic Nature of the Citric Acid Cycle
- The citric acid cycle has a dual role in metabolism, acting in both catabolic and anabolic pathways.
- Catabolic function: oxidation of acetyl-CoA to CO2.
- Anabolic function: citric acid cycle intermediates as precursors for biosynthetic pathways.
- Anaplerotic reactions replenish citric acid cycle intermediates depleted by anabolic processes.
- Pyruvate carboxylase is a key anaplerotic reaction replenishing oxaloacetate when acetyl-CoA is high.
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Description
Explore the metabolism of various monosaccharides including fructose, galactose, and mannose. This quiz covers how these sugars are processed in the body, their energy contributions, and the implications of hereditary fructose intolerance. Test your understanding of their metabolic pathways and significance in vertebrates.
