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Questions and Answers
What is the initial product formed from the conversion of fructose in the liver?
What is the initial product formed from the conversion of fructose in the liver?
Which enzyme is responsible for converting glyceraldehyde into glyceraldehyde-3-P?
Which enzyme is responsible for converting glyceraldehyde into glyceraldehyde-3-P?
How is fructose metabolized in muscles and adipose tissues?
How is fructose metabolized in muscles and adipose tissues?
What unique role does fructose serve in the human body?
What unique role does fructose serve in the human body?
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What metabolic pathway does glyceraldehyde-3-P enter after its formation?
What metabolic pathway does glyceraldehyde-3-P enter after its formation?
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Which process occurs due to excess glucose in diabetes mellitus?
Which process occurs due to excess glucose in diabetes mellitus?
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What is the outcome of combining dihydroxyacetone phosphate with glyceraldehyde-3-P?
What is the outcome of combining dihydroxyacetone phosphate with glyceraldehyde-3-P?
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Which enzyme is deficient in muscles and adipose tissues for fructose metabolism?
Which enzyme is deficient in muscles and adipose tissues for fructose metabolism?
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What is the primary source of galactose in the diet?
What is the primary source of galactose in the diet?
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Which enzyme is responsible for the conversion of galactose to galactose-1-P in the liver?
Which enzyme is responsible for the conversion of galactose to galactose-1-P in the liver?
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Which of the following conditions can lead to fasting hypoglycemia?
Which of the following conditions can lead to fasting hypoglycemia?
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What is a common cause of stimulative hypoglycemia?
What is a common cause of stimulative hypoglycemia?
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What essential biochemical process occurs in the liver involving galactose?
What essential biochemical process occurs in the liver involving galactose?
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Which of the following does NOT contribute to glucosuria?
Which of the following does NOT contribute to glucosuria?
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Which product is formed directly from the combination of glucose and UDP-galactose?
Which product is formed directly from the combination of glucose and UDP-galactose?
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What is the normal fasting blood glucose level range?
What is the normal fasting blood glucose level range?
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What is the renal threshold for glucose concentration in blood?
What is the renal threshold for glucose concentration in blood?
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What condition is defined by plasma glucose levels dropping below 60 mg/dl?
What condition is defined by plasma glucose levels dropping below 60 mg/dl?
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Which disorder is associated with defective glucose production leading to hypoglycemia?
Which disorder is associated with defective glucose production leading to hypoglycemia?
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Which substance is NOT a direct source of blood glucose?
Which substance is NOT a direct source of blood glucose?
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What is a characteristic of essential reactive hypoglycemia?
What is a characteristic of essential reactive hypoglycemia?
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Which of the following can occur during pregnancy, affecting glucose levels?
Which of the following can occur during pregnancy, affecting glucose levels?
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Which process describes the conversion of glycogen back to glucose?
Which process describes the conversion of glycogen back to glucose?
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What condition is categorized under stimulative hypoglycemia due to metabolic errors?
What condition is categorized under stimulative hypoglycemia due to metabolic errors?
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Study Notes
Metabolism of Other Hexoses and Blood Glucose
- Topic: Metabolism of other hexoses and blood glucose.
- Location: Medical Biochemistry and Molecular Biology Department, Faculty of Medicine - Menoufia University
Fructose Metabolism
- Sources of fructose: Sucrose, diet (honey, fruits, vegetables)
- Importance of fructose: 15% of total body energy, only source of energy for spermatozoa.
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Fructose metabolism in the liver, kidney, and intestine:
- Contains fructokinase, which converts fructose into fructose-1-P.
- Fructose-1-P is hydrolyzed by aldolase B to form dihydroxyacetone phosphate and glyceraldehyde.
Fructose Metabolism in Muscles and Adipose Tissues
- These tissues lack fructokinase but contain hexokinase.
- Fructose is phosphorylated by hexokinase to fructose-6-phosphate.
- Enters glycolysis, generating 2 pyruvate molecules and energy.
Glyceraldehyde
- Triokinase converts glyceraldehyde to glyceraldehyde-3-P.
- Glyceraldehyde-3-P enters glycolysis and combines with dihydroxyacetone phosphate to yield glucose.
Glucose Conversion to Fructose in Specific Tissues
- In testes, lenses, peripheral nerves, and renal glomeruli, glucose is converted to fructose via aldolase reductase and sorbitol dehydrogenase.
- In diabetes mellitus, excess glucose is converted into sorbitol in the lens, which can cause cataracts.
Galactose Metabolism
- Sources of galactose: Dietary milk (lactose)
- Importance of galactose: Structural component of lactose, glycolipids, glycoproteins, and proteoglycans.
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Galactose conversion to glucose in the liver:
- Galactose is phosphorylated by galactokinase into galactose-1-phosphate.
- Galactose-1-phosphate is transformed into UDP-galactose and glucose using uridyl transferase and UDP-galactose-4-epimerase.
Conversion of Glucose to Galactose in Mammary Gland
- Glucose, using hexokinase, is transformed to glucose-6-phosphate, and then glucose-1-phosphate.
- Glucose-1-phosphate is converted to UDP-glucose and using uridyl transferase eventually resulting in UDP-galactose via UDP-galactose 4-epimerase forming UDP-glucose and lactose.
Normal Blood Glucose Levels
- Fasting blood glucose (FBG): 70-110 mg/dL
- 2-hour postprandial glucose (2-hr PP): up to 140 mg/dL
- Sources of blood glucose: Dietary carbohydrates (glucose, galactose, fructose), gluconeogenic substances (e.g., amino acids, lactate, glycerol), liver glycogen (glycogenolysis).
Variations in Blood Glucose: Hypoglycemia
- Definition: Plasma glucose below 60 mg/dL.
- Symptoms: Faintness, dizziness, lethargy, progressing to coma and permanent cerebral damage if untreated.
- Causes: Stimulative hypoglycemia (drugs, inborn errors of metabolism), post-gastrectomy, excess alcohol intake, deficient glucose production (endocrine disease, liver disease, renal disease) and fasting hypoglycemia (starvation, malnutrition, inborn errors of metabolism, pancreatic disease).
Glucosuria
- Definition: Glucose in urine detectable by ordinary methods.
- Occurrence: When venous blood glucose exceeds the renal threshold (180 mg/dL).
- Causes: Diabetes mellitus, Renal glucosuria (low renal threshold, inherited defects, drugs, pregnancy, Fanconi's syndrome).
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Description
This quiz explores the metabolism of hexoses, specifically focusing on fructose. It covers the pathways of fructose metabolism in various organs, its role in energy production, and how it interacts with other metabolic processes, including glycolysis. Test your knowledge on the biochemical transformations of fructose and its significance in human physiology.
