What complications do individuals with galactokinase deficiency typically avoid?
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Hepatic and renal complications.
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What complications do individuals with galactokinase deficiency typically avoid?
Hepatic and renal complications.
Where does the synthesis of amino sugars mostly occur?
In the connective tissue.
Is galactose an essential nutrient?
No, it is not essential because UDP-glucose can be converted to UDP-galactose.
What percentage of glucose is utilized for the synthesis of amino sugars?
About 20%.
What is the major dietary source of fructose?
Sucrose (cane sugar) and high-fructose corn syrups.
What is formed when galactose is shunted in galactosemia?
Galactitol.
What condition results from the phosphorylation of galactose?
Galactosemia and galactosuria.
What is an amino sugar?
A compound formed when a hydroxyl group of a sugar is replaced by an amino group.
What is the major precursor for glucosamine and other amino sugars?
Fructose 6-phosphate.
Where is aldose reductase found in the body?
In many tissues like lens, retina, kidney, placenta, Schwann cells, erythrocytes, and seminal vesicles.
Name some important amino sugars.
Glucosamine, galactosamine, mannosamine, sialic acid.
What is the principal dietary source of galactose?
Lactose, present in milk and milk products.
What is the primary function of the glyoxylate cycle?
To convert fat into carbohydrates.
What are the clinical symptoms of galactosemia?
Loss of weight, hepatosplenomegaly, jaundice, mental retardation, cataract, amino aciduria, and albuminuria.
What are some pathological changes associated with sorbitol accumulation in diabetes?
Cataract formation, peripheral neuropathy, and nephropathy.
What is a common early symptom of galactokinase deficiency?
Development of cataracts within the first year after birth.
Which enzyme hydrolyzes lactose to galactose and glucose?
Lactase (E-galactosidase).
What enzyme primarily phosphorylates fructose in the body?
Fructokinase.
What enzyme converts UDP-galactose to UDP-glucose?
UDP hexose 4-epimerase.
How does the entry of fructose into cells differ from glucose?
Fructose entry is not controlled by insulin, unlike glucose.
What role do mucopolysaccharidoses play in understanding health and disease?
They help elucidate the role of lysosomes.
What is the role of sorbitol dehydrogenase in fructose metabolism?
It oxidizes sorbitol to fructose using NAD+.
What are the consequences of mucopolysaccharidoses?
Accumulation of GAGs leading to skeletal deformities and mental retardation.
What are mucopolysaccharidoses?
Lysosomal storage diseases caused by enzyme defects in the degradation of glycosaminoglycans.
How is galactose produced within cells?
From the lysosomal degradation of glycoproteins and glycolipids.
What is classical galactosemia caused by?
Deficiency of the enzyme galactose 1-phosphate uridyltransferase.
What happens to glucose in uncontrolled diabetes?
Large amounts enter insulin-independent cells, leading to increased sorbitol production.
Why is fructose preferred for energy needs of sperm cells?
Due to the presence of the sorbitol pathway.
Where does the glyoxylate cycle occur?
In glyoxysomes.
What is the major source of energy for living cells?
Carbohydrates.
Is the entry of galactose into cells dependent on insulin?
No, it is not dependent on insulin.
What enzyme phosphorylates galactose to galactose 1-phosphate?
Galactokinase.
What is the product of fructose 1-phosphate cleavage?
Glyceraldehyde and dihydroxyacetone phosphate (DHAP).
What is the starting molecule for the glyoxylate cycle?
Acetyl CoA.
What is the normal fasting blood level of glucose?
70-100 mg/dl.
What is the metabolism of glucose 6-phosphate?
Glucose 6-phosphate can enter glycolysis, the pentose phosphate pathway, or be converted to glycogen.
Can animals synthesize carbohydrates from fat?
No, they cannot carry out the net synthesis of carbohydrate from fat.
What happens to galactose levels in galactosemia?
Galactose metabolism is impaired, leading to increased levels of galactose in circulation (galactosemia) and urine (galactosuria).
What does galactose 1-phosphate react with to form UDP-galactose?
UDP-glucose, in the presence of galactose 1-phosphate uridyltransferase.
Which enzyme has a low affinity for fructose and acts as a minor pathway?
Hexokinase.
What are the metabolic pathways that glucose participates in?
Glycolysis, gluconeogenesis, glycogenesis, glycogenolysis, hexose monophosphate shunt, uronic acid pathway.
What does acetyl CoA condense with to form citrate in the glyoxylate cycle?
Oxaloacetate.
What is the role of aldose reductase in galactose metabolism?
It converts accumulated galactose to galactitol, which can lead to cataract development.
What is essential fructosuria?
A condition due to deficiency of hepatic fructokinase, leading to fructose excretion in urine.
What is the role of triokinase in carbohydrate metabolism?
Triokinase phosphorylates glyceraldehyde to glyceraldehyde 3-phosphate.
What enzyme cleaves isocitrate in the glyoxylate cycle?
Isocitrate lyase.
What is the consequence of high levels of galactose 1-phosphate in the liver?
It results in the depletion of inorganic phosphate and inhibits glycogen phosphorylase, leading to hypoglycemia.
What is glycogen metabolism?
Glycogen metabolism involves glycogen synthesis (glycogenesis) and breakdown (glycogenolysis) to maintain glucose levels.
What is UDP-galactose used for?
As an active donor of galactose for synthetic reactions involving compounds like lactose and glycoproteins.
What is the consequence of high fructose consumption?
Depletion of intracellular inorganic phosphate (Pi) and adverse effects on liver metabolism.
What causes hereditary fructose intolerance?
Absence of the enzyme aldolase B, leading to accumulation of fructose 1-phosphate.
What health complications are linked to high intake of fructose or sucrose?
Ingestion of large quantities is linked with various health complications, including increased lipogenesis.
What is the end product of the glyoxylate cycle that enters the citric acid cycle?
Malate.
What is the hexose monophosphate shunt?
A metabolic pathway that generates NADPH and ribose-5-phosphate from glucose-6-phosphate.
How does fructose metabolism differ from glucose metabolism in the liver?
Fructose is metabolized more rapidly than glucose because it bypasses the rate-limiting step in glycolysis.
What enzyme catalyzes the reaction of glyoxylate combining with acetyl CoA to form malate?
Malate synthase.
What is produced from pyruvate in carbohydrate metabolism?
Acetyl CoA.
What effect do aminopyrine and antipyrine have on pentosuric patients?
They increase the excretion of L-xylulose.
What is gluconeogenesis?
The synthesis of glucose from noncarbohydrate precursors.
What is the significance of the HMP shunt in red blood cells?
It produces NADPH, maintaining erythrocyte membrane integrity and preventing methemoglobin accumulation.
What are glycogen storage diseases?
A group of inherited disorders that affect glycogen metabolism.
What is the energetics of the TCA cycle?
The TCA cycle produces ATP, NADH, and FADH2, which are used in oxidative phosphorylation.
What are the products of the cleavage of isocitrate?
Succinate and glyoxylate.
How many ATP are formed during aerobic glycolysis?
8 ATP.
How many ATP are formed during anaerobic glycolysis?
2 ATP.
What is the treatment for galactosemia?
A diet deprived of galactose and lactose.
What is the synthesis of glucose from non-carbohydrate sources called?
Gluconeogenesis.
How does the glyoxylate cycle relate to gluconeogenesis?
Succinate is converted to oxaloacetate and then to glucose.
What disease is caused by a defect in glucose 6-phosphatase?
von Gierke’s disease (Type I).
What happens to glucose to fructose conversion in diabetes mellitus?
It is impaired, leading to sorbitol accumulation.
What is TPP in carbohydrate metabolism?
Thiamine pyrophosphate, a coenzyme involved in decarboxylation reactions.
How is galactosemia diagnosed?
By measuring the activity of galactose 1-phosphate uridyltransferase in erythrocytes.
Why is the citric acid cycle considered the final common metabolic pathway?
It oxidizes carbohydrates, fats, and proteins, integrating various metabolic pathways.
Is essential pentosuria symptomatic?
No, it is asymptomatic and individuals suffer from no ill effects.
How many ATP are generated from the complete oxidation of one mole of glucose?
38 ATP.
What does UDPG stand for?
Uridine diphosphate glucose, a key intermediate in glycogen synthesis.
What is the consequence of glucose 6-phosphate dehydrogenase deficiency?
It results in hemolysis of RBC, causing hemolytic anemia.
What is essential fructosuria?
A benign condition caused by the deficiency of fructokinase, leading to fructose accumulation.
What is essential pentosuria?
A rare genetic disorder related to the deficiency of NADP-dependent enzyme xylitol dehydrogenase.
How does high fructose consumption relate to atherosclerosis?
It increases glycolysis and lipogenesis, leading to elevated triacylglycerol levels.
What does succinate convert to in the glyoxylate cycle?
Oxaloacetate.
What happens due to the enzyme defect in essential pentosuria?
L-xylulose cannot be converted to xylitol, leading to large amounts of L-xylulose excreted in urine.
What enzyme reduces glucose to sorbitol?
Aldose reductase, in the presence of NADPH.
What is the polyol pathway?
It involves the conversion of glucose to fructose via sorbitol and is absent in the liver.
What is the final common oxidative pathway for all foodstuffs?
Citric acid cycle.
What is the primary function of liver glycogen?
To maintain blood glucose levels, especially between meals.
What is glycogen?
The storage form of glucose.
Why can't humans synthesize vitamin C?
Due to the absence of the enzyme L-gulonolactone oxidase.
What is the conversion of pyruvate to acetyl CoA?
A critical step linking glycolysis to the citric acid cycle, catalyzed by the pyruvate dehydrogenase complex.
What is the defect in galactokinase deficiency?
It affects the conversion of galactose to galactose 1-phosphate.
What is the consequence of insufficient glucose supply to the brain?
It may lead to coma and death.
What is the Cori cycle?
A metabolic pathway that recycles lactate produced by anaerobic glycolysis in muscles back to glucose in the liver.
What enzyme defect leads to galactosemia?
Galactose 1-phosphate uridyltransferase.
What is glycogenolysis?
The process of breaking down glycogen into glucose.
What are glycogen storage diseases characterized by?
Deposition of normal or abnormal glycogen in tissues, leading to muscular weakness or death.
What does the hexose monophosphate shunt generate?
NADPH and pentoses.
What is galactosemia associated with?
The development of cataract due to galactitol accumulation.
What is the role of UDP-glucuronate in metabolism?
It is involved in the synthesis of glucuronides.
What is 2,3-BPG?
2,3-bisphosphoglycerate, a metabolite that regulates oxygen release from hemoglobin.
What can prolonged hyperglycemia lead to?
Accumulation of sorbitol, resulting in cataract, nephropathy, peripheral neuropathy.
What is galactosemia?
A genetic disorder resulting from the inability to metabolize galactose due to enzyme deficiency.
What is glucuronate involved in?
Conjugation of bilirubin, steroid hormones, and detoxification of drugs.
What are amino sugars essential for?
Components of glycosaminoglycans, glycolipids, and glycoproteins.
