Biochemistry-U-Satyanaryan-4th-Edition-254-294

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What complications do individuals with galactokinase deficiency typically avoid?

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Hepatic and renal complications.

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Disorders of Galactose Metabolism

What complications do individuals with galactokinase deficiency typically avoid?

Hepatic and renal complications.

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Amino Sugars and Their Importance

Where does the synthesis of amino sugars mostly occur?

In the connective tissue.

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Metabolism of Galactose

Is galactose an essential nutrient?

No, it is not essential because UDP-glucose can be converted to UDP-galactose.

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Amino Sugars and Their Importance

What percentage of glucose is utilized for the synthesis of amino sugars?

About 20%.

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Metabolism of Fructose

What is the major dietary source of fructose?

Sucrose (cane sugar) and high-fructose corn syrups.

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Disorders of Galactose Metabolism

What is formed when galactose is shunted in galactosemia?

Galactitol.

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Disorders of Galactose Metabolism

What condition results from the phosphorylation of galactose?

Galactosemia and galactosuria.

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Amino Sugars and Their Importance

What is an amino sugar?

A compound formed when a hydroxyl group of a sugar is replaced by an amino group.

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Amino Sugars and Their Importance

What is the major precursor for glucosamine and other amino sugars?

Fructose 6-phosphate.

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Metabolism of Fructose

Where is aldose reductase found in the body?

In many tissues like lens, retina, kidney, placenta, Schwann cells, erythrocytes, and seminal vesicles.

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Amino Sugars and Their Importance

Name some important amino sugars.

Glucosamine, galactosamine, mannosamine, sialic acid.

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Metabolism of Galactose

What is the principal dietary source of galactose?

Lactose, present in milk and milk products.

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Glyoxylate Cycle and Its Significance

What is the primary function of the glyoxylate cycle?

To convert fat into carbohydrates.

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Disorders of Galactose Metabolism

What are the clinical symptoms of galactosemia?

Loss of weight, hepatosplenomegaly, jaundice, mental retardation, cataract, amino aciduria, and albuminuria.

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Sorbitol/Polyol Pathway

What are some pathological changes associated with sorbitol accumulation in diabetes?

Cataract formation, peripheral neuropathy, and nephropathy.

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Disorders of Galactose Metabolism

What is a common early symptom of galactokinase deficiency?

Development of cataracts within the first year after birth.

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Metabolism of Galactose

Which enzyme hydrolyzes lactose to galactose and glucose?

Lactase (E-galactosidase).

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Metabolism of Fructose

What enzyme primarily phosphorylates fructose in the body?

Fructokinase.

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Metabolism of Galactose

What enzyme converts UDP-galactose to UDP-glucose?

UDP hexose 4-epimerase.

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Metabolism of Fructose

How does the entry of fructose into cells differ from glucose?

Fructose entry is not controlled by insulin, unlike glucose.

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Mucopolysaccharidoses

What role do mucopolysaccharidoses play in understanding health and disease?

They help elucidate the role of lysosomes.

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Metabolism of Fructose

What is the role of sorbitol dehydrogenase in fructose metabolism?

It oxidizes sorbitol to fructose using NAD+.

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Mucopolysaccharidoses

What are the consequences of mucopolysaccharidoses?

Accumulation of GAGs leading to skeletal deformities and mental retardation.

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Mucopolysaccharidoses

What are mucopolysaccharidoses?

Lysosomal storage diseases caused by enzyme defects in the degradation of glycosaminoglycans.

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Metabolism of Galactose

How is galactose produced within cells?

From the lysosomal degradation of glycoproteins and glycolipids.

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Disorders of Galactose Metabolism

What is classical galactosemia caused by?

Deficiency of the enzyme galactose 1-phosphate uridyltransferase.

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Sorbitol/Polyol Pathway

What happens to glucose in uncontrolled diabetes?

Large amounts enter insulin-independent cells, leading to increased sorbitol production.

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Metabolism of Fructose

Why is fructose preferred for energy needs of sperm cells?

Due to the presence of the sorbitol pathway.

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Glyoxylate Cycle and Its Significance

Where does the glyoxylate cycle occur?

In glyoxysomes.

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Metabolism of Carbohydrates

What is the major source of energy for living cells?

Carbohydrates.

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Metabolism of Galactose

Is the entry of galactose into cells dependent on insulin?

No, it is not dependent on insulin.

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Metabolism of Galactose

What enzyme phosphorylates galactose to galactose 1-phosphate?

Galactokinase.

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Metabolism of Fructose

What is the product of fructose 1-phosphate cleavage?

Glyceraldehyde and dihydroxyacetone phosphate (DHAP).

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Glyoxylate Cycle and Its Significance

What is the starting molecule for the glyoxylate cycle?

Acetyl CoA.

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Metabolism of Carbohydrates

What is the normal fasting blood level of glucose?

70-100 mg/dl.

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Metabolism of Glucose

What is the metabolism of glucose 6-phosphate?

Glucose 6-phosphate can enter glycolysis, the pentose phosphate pathway, or be converted to glycogen.

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Glyoxylate Cycle and Its Significance

Can animals synthesize carbohydrates from fat?

No, they cannot carry out the net synthesis of carbohydrate from fat.

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Disorders of Galactose Metabolism

What happens to galactose levels in galactosemia?

Galactose metabolism is impaired, leading to increased levels of galactose in circulation (galactosemia) and urine (galactosuria).

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Metabolism of Galactose

What does galactose 1-phosphate react with to form UDP-galactose?

UDP-glucose, in the presence of galactose 1-phosphate uridyltransferase.

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Metabolism of Fructose

Which enzyme has a low affinity for fructose and acts as a minor pathway?

Hexokinase.

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Metabolism of Carbohydrates

What are the metabolic pathways that glucose participates in?

Glycolysis, gluconeogenesis, glycogenesis, glycogenolysis, hexose monophosphate shunt, uronic acid pathway.

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Glyoxylate Cycle and Its Significance

What does acetyl CoA condense with to form citrate in the glyoxylate cycle?

Oxaloacetate.

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Disorders of Galactose Metabolism

What is the role of aldose reductase in galactose metabolism?

It converts accumulated galactose to galactitol, which can lead to cataract development.

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Defects in Fructose Metabolism

What is essential fructosuria?

A condition due to deficiency of hepatic fructokinase, leading to fructose excretion in urine.

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Metabolism of Fructose

What is the role of triokinase in carbohydrate metabolism?

Triokinase phosphorylates glyceraldehyde to glyceraldehyde 3-phosphate.

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Glyoxylate Cycle and Its Significance

What enzyme cleaves isocitrate in the glyoxylate cycle?

Isocitrate lyase.

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Disorders of Galactose Metabolism

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.

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Glycogen Storage Diseases

What is glycogen metabolism?

Glycogen metabolism involves glycogen synthesis (glycogenesis) and breakdown (glycogenolysis) to maintain glucose levels.

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Metabolism of Galactose

What is UDP-galactose used for?

As an active donor of galactose for synthetic reactions involving compounds like lactose and glycoproteins.

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Defects in Fructose Metabolism

What is the consequence of high fructose consumption?

Depletion of intracellular inorganic phosphate (Pi) and adverse effects on liver metabolism.

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Defects in Fructose Metabolism

What causes hereditary fructose intolerance?

Absence of the enzyme aldolase B, leading to accumulation of fructose 1-phosphate.

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Metabolism of Fructose

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.

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Glyoxylate Cycle and Its Significance

What is the end product of the glyoxylate cycle that enters the citric acid cycle?

Malate.

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Synthesis of Glucuronate from Glucose

What is the hexose monophosphate shunt?

A metabolic pathway that generates NADPH and ribose-5-phosphate from glucose-6-phosphate.

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Metabolism of Fructose

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.

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Glyoxylate Cycle and Its Significance

What enzyme catalyzes the reaction of glyoxylate combining with acetyl CoA to form malate?

Malate synthase.

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Metabolism of Carbohydrates

What is produced from pyruvate in carbohydrate metabolism?

Acetyl CoA.

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Essential Pentosuria and Enzyme Deficiency

What effect do aminopyrine and antipyrine have on pentosuric patients?

They increase the excretion of L-xylulose.

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Metabolism of Carbohydrates

What is gluconeogenesis?

The synthesis of glucose from noncarbohydrate precursors.

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Metabolism of Carbohydrates

What is the significance of the HMP shunt in red blood cells?

It produces NADPH, maintaining erythrocyte membrane integrity and preventing methemoglobin accumulation.

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Glycogen Storage Diseases

What are glycogen storage diseases?

A group of inherited disorders that affect glycogen metabolism.

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Glyoxylate Cycle and Its Significance

What is the energetics of the TCA cycle?

The TCA cycle produces ATP, NADH, and FADH2, which are used in oxidative phosphorylation.

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Glyoxylate Cycle and Its Significance

What are the products of the cleavage of isocitrate?

Succinate and glyoxylate.

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Metabolism of Carbohydrates

How many ATP are formed during aerobic glycolysis?

8 ATP.

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Metabolism of Carbohydrates

How many ATP are formed during anaerobic glycolysis?

2 ATP.

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Disorders of Galactose Metabolism

What is the treatment for galactosemia?

A diet deprived of galactose and lactose.

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Synthesis of Glucuronate from Glucose

What is the synthesis of glucose from non-carbohydrate sources called?

Gluconeogenesis.

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Glyoxylate Cycle and Its Significance

How does the glyoxylate cycle relate to gluconeogenesis?

Succinate is converted to oxaloacetate and then to glucose.

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Disorders of Galactose Metabolism

What disease is caused by a defect in glucose 6-phosphatase?

von Gierke’s disease (Type I).

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Sorbitol/Polyol Pathway

What happens to glucose to fructose conversion in diabetes mellitus?

It is impaired, leading to sorbitol accumulation.

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Amino Sugars and Their Importance

What is TPP in carbohydrate metabolism?

Thiamine pyrophosphate, a coenzyme involved in decarboxylation reactions.

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Disorders of Galactose Metabolism

How is galactosemia diagnosed?

By measuring the activity of galactose 1-phosphate uridyltransferase in erythrocytes.

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Glyoxylate Cycle and Its Significance

Why is the citric acid cycle considered the final common metabolic pathway?

It oxidizes carbohydrates, fats, and proteins, integrating various metabolic pathways.

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Essential Pentosuria and Enzyme Deficiency

Is essential pentosuria symptomatic?

No, it is asymptomatic and individuals suffer from no ill effects.

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Metabolism of Carbohydrates

How many ATP are generated from the complete oxidation of one mole of glucose?

38 ATP.

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Glycogen Storage Diseases

What does UDPG stand for?

Uridine diphosphate glucose, a key intermediate in glycogen synthesis.

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Metabolism of Carbohydrates

What is the consequence of glucose 6-phosphate dehydrogenase deficiency?

It results in hemolysis of RBC, causing hemolytic anemia.

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Defects in Fructose Metabolism

What is essential fructosuria?

A benign condition caused by the deficiency of fructokinase, leading to fructose accumulation.

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Essential Pentosuria and Enzyme Deficiency

What is essential pentosuria?

A rare genetic disorder related to the deficiency of NADP-dependent enzyme xylitol dehydrogenase.

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Metabolism of Fructose

How does high fructose consumption relate to atherosclerosis?

It increases glycolysis and lipogenesis, leading to elevated triacylglycerol levels.

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Glyoxylate Cycle and Its Significance

What does succinate convert to in the glyoxylate cycle?

Oxaloacetate.

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Essential Pentosuria and Enzyme Deficiency

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.

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Sorbitol/Polyol Pathway

What enzyme reduces glucose to sorbitol?

Aldose reductase, in the presence of NADPH.

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Sorbitol/Polyol Pathway

What is the polyol pathway?

It involves the conversion of glucose to fructose via sorbitol and is absent in the liver.

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Metabolism of Carbohydrates

What is the final common oxidative pathway for all foodstuffs?

Citric acid cycle.

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Metabolism of Carbohydrates

What is the primary function of liver glycogen?

To maintain blood glucose levels, especially between meals.

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Metabolism of Carbohydrates

What is glycogen?

The storage form of glucose.

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Amino Sugars and Their Importance

Why can't humans synthesize vitamin C?

Due to the absence of the enzyme L-gulonolactone oxidase.

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Metabolism of Fructose

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.

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Disorders of Galactose Metabolism

What is the defect in galactokinase deficiency?

It affects the conversion of galactose to galactose 1-phosphate.

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Metabolism of Carbohydrates

What is the consequence of insufficient glucose supply to the brain?

It may lead to coma and death.

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Metabolism of Galactose

What is the Cori cycle?

A metabolic pathway that recycles lactate produced by anaerobic glycolysis in muscles back to glucose in the liver.

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Disorders of Galactose Metabolism

What enzyme defect leads to galactosemia?

Galactose 1-phosphate uridyltransferase.

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Glycogen Storage Diseases

What is glycogenolysis?

The process of breaking down glycogen into glucose.

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Metabolism of Carbohydrates

What are glycogen storage diseases characterized by?

Deposition of normal or abnormal glycogen in tissues, leading to muscular weakness or death.

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Metabolism of Carbohydrates

What does the hexose monophosphate shunt generate?

NADPH and pentoses.

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Disorders of Galactose Metabolism

What is galactosemia associated with?

The development of cataract due to galactitol accumulation.

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Synthesis of Glucuronate from Glucose

What is the role of UDP-glucuronate in metabolism?

It is involved in the synthesis of glucuronides.

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Metabolism of Fructose

What is 2,3-BPG?

2,3-bisphosphoglycerate, a metabolite that regulates oxygen release from hemoglobin.

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Metabolism of Fructose

What can prolonged hyperglycemia lead to?

Accumulation of sorbitol, resulting in cataract, nephropathy, peripheral neuropathy.

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Disorders of Galactose Metabolism

What is galactosemia?

A genetic disorder resulting from the inability to metabolize galactose due to enzyme deficiency.

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Metabolism of Carbohydrates

What is glucuronate involved in?

Conjugation of bilirubin, steroid hormones, and detoxification of drugs.

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Amino Sugars and Their Importance

What are amino sugars essential for?

Components of glycosaminoglycans, glycolipids, and glycoproteins.

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