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Questions and Answers
What is a biochemical hallmark of Von Gierke’s disease?
What is a biochemical hallmark of Von Gierke’s disease?
- Exercise intolerance
- Hemolysis
- No lactic acidosis
- Hyperlipidemia (correct)
What clinical feature is associated with Pompe's disease?
What clinical feature is associated with Pompe's disease?
- Lactic acidosis
- Floppy infant syndrome (correct)
- Massive hepatomegaly
- Liver cirrhosis
Which factor predominantly favors glycogen synthesis?
Which factor predominantly favors glycogen synthesis?
- Glucagon
- Epinephrine
- Cortisol
- Insulin (correct)
What type of glycogen storage disorder is characterized by no lactic acidosis and no hyperuricemia?
What type of glycogen storage disorder is characterized by no lactic acidosis and no hyperuricemia?
Which enzyme defect is present in McArdle’s disease?
Which enzyme defect is present in McArdle’s disease?
What is a common clinical feature of Type IV Anderson's disease?
What is a common clinical feature of Type IV Anderson's disease?
Which glycogen storage disorder is associated with the 2nd wind phenomenon after exercise?
Which glycogen storage disorder is associated with the 2nd wind phenomenon after exercise?
Which of the following conditions is a classic feature of Type VI Her’s disease?
Which of the following conditions is a classic feature of Type VI Her’s disease?
Which type of hyperlipoproteinemia is characterized by eruptive xanthomas and lipemia retinalis?
Which type of hyperlipoproteinemia is characterized by eruptive xanthomas and lipemia retinalis?
What is the primary role of pyruvate dehydrogenase (PDH) in metabolism?
What is the primary role of pyruvate dehydrogenase (PDH) in metabolism?
Which amino acid is classified as having an aliphatic branched side chain?
Which amino acid is classified as having an aliphatic branched side chain?
Corneal arcus is a characteristic finding in which condition?
Corneal arcus is a characteristic finding in which condition?
What is a typical appearance of palmar xanthoma?
What is a typical appearance of palmar xanthoma?
Which of the following amino acids contains a sulfur group in its side chain?
Which of the following amino acids contains a sulfur group in its side chain?
What occurs to pyruvate when there is a defect in the PDH complex?
What occurs to pyruvate when there is a defect in the PDH complex?
Which of the following statements about glycogen metabolism is accurate?
Which of the following statements about glycogen metabolism is accurate?
Which glycogen linkage is responsible for branching in its structure?
Which glycogen linkage is responsible for branching in its structure?
What role does G-6-phosphatase play in glycogen metabolism?
What role does G-6-phosphatase play in glycogen metabolism?
What distinguishes Type II hyperlipoproteinemia from Type III?
What distinguishes Type II hyperlipoproteinemia from Type III?
How many ATP molecules are consumed during the formation of Argininosuccinate in the urea cycle?
How many ATP molecules are consumed during the formation of Argininosuccinate in the urea cycle?
Which of the following amino acids is classified as a basic amino acid?
Which of the following amino acids is classified as a basic amino acid?
What kind of metabolic defect does Leigh syndrome involve?
What kind of metabolic defect does Leigh syndrome involve?
What type of xanthoma is described as a 'bunch of grapes'?
What type of xanthoma is described as a 'bunch of grapes'?
During glycogen synthesis, which molecule serves as an intermediate that donates glucose units?
During glycogen synthesis, which molecule serves as an intermediate that donates glucose units?
What is the primary organ involved in the urea cycle?
What is the primary organ involved in the urea cycle?
Which molecule serves as the allosteric activator of the rate-limiting step (CPS I) in the urea cycle?
Which molecule serves as the allosteric activator of the rate-limiting step (CPS I) in the urea cycle?
Which step in the urea cycle is considered the rate-limiting step?
Which step in the urea cycle is considered the rate-limiting step?
Which of the following is NOT a substrate for gluconeogenesis?
Which of the following is NOT a substrate for gluconeogenesis?
What is the product of the reaction catalyzed by Argininosuccinate lyase?
What is the product of the reaction catalyzed by Argininosuccinate lyase?
Which organelle is primarily involved in the urea cycle?
Which organelle is primarily involved in the urea cycle?
What is formed when Ornithine reacts with Carbamoyl phosphate?
What is formed when Ornithine reacts with Carbamoyl phosphate?
What enzyme defect is associated with Hereditary Fructose Intolerance?
What enzyme defect is associated with Hereditary Fructose Intolerance?
Which of the following molecules directly enters the TCA cycle after being formed in the urea cycle?
Which of the following molecules directly enters the TCA cycle after being formed in the urea cycle?
Which of the following symptoms is NOT associated with Galactosemia?
Which of the following symptoms is NOT associated with Galactosemia?
Which metabolic process prominently produces 10 ATPs in one cycle?
Which metabolic process prominently produces 10 ATPs in one cycle?
Which of the following inhibitors affects succinate dehydrogenase?
Which of the following inhibitors affects succinate dehydrogenase?
What is the primary role of pyruvate carboxylase in the TCA cycle?
What is the primary role of pyruvate carboxylase in the TCA cycle?
Which vitamin is associated with coenzyme A in the TCA cycle?
Which vitamin is associated with coenzyme A in the TCA cycle?
Which of the following statements about the TCA cycle is true?
Which of the following statements about the TCA cycle is true?
Which test is positive for detecting reducing sugars in metabolic disorders?
Which test is positive for detecting reducing sugars in metabolic disorders?
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Study Notes
Muscle Metabolism
- Anaerobic glycolysis produces 3 ATP without the hexokinase step.
- Glycogen synthesis is promoted by insulin.
- Glycogenolysis is stimulated by glucagon and epinephrine.
Glycogen Storage Disorders (GSD)
- Type 1 / Von Gierke's Disease: Caused by glucose-6-phosphatase deficiency; features massive hepatomegaly, hypoglycemia, hyperuricemia, hyperlipidemia, and lactic acidosis.
- Type 2 / Pompe's Disease: Caused by acid α-1,6-glucosidase deficiency; characterized by hypertrophic cardiomyopathy and severe hypotonia in infants.
- Type 3 / Cori's Disease: Caused by debranching enzyme defect; no lactic acidosis or hyperuricemia, may lead to liver cirrhosis.
- Type 4 / Anderson's Disease: Due to branching enzyme deficiency; results in liver failure, typically fatal by age 5.
- Type 5 / McArdle's Disease: Caused by muscle glycogen phosphorylase deficiency; exhibits the "second wind" phenomenon during exercise.
- Type 6 / Her's Disease: Affects hepatic glycogen phosphorylase; characterized by exercise intolerance and eruptive xanthoma.
Hyperlipoproteinemias
- Type II: Familial hypercholesterolemia leads to corneal arcus and xanthomas, including Achilles tendon xanthoma.
- Type III: Familial dysbetalipoproteinemia manifests with tubero-eruptive and palmar xanthomas.
Amino Acid Chemistry
- Most amino acids are α-amino acids with a general structure: NH2-C-COOH.
- Classification includes aliphatic (e.g., glycine, alanine), aromatic, sulfur-containing (e.g., cysteine), and basic amino acids (e.g., histidine, lysine).
Pyruvate Dehydrogenase
- Converts pyruvate to Acetyl-CoA, linking glycolysis to the TCA cycle.
- Excess carbohydrates shift towards fatty acid synthesis.
- Inhibitions in the PDH complex can cause lactic acidosis due to increased pyruvate conversion to lactate leading to Leigh syndrome.
Glycogen Metabolism
- Glycogen is stored in the liver (for glucose during fasting) and skeletal muscle (for exercise energy).
- Glycogen synthesis involves UDP-glucose formation and glycogen synthase action.
- Glycogenolysis starts in fasting states, primarily via glycogen phosphorylase and debranching enzymes, with glucose-6-phosphate formation facilitated by glucose-6-phosphatase.
Metabolic Disorders
- Hereditary Fructose Intolerance (HFI): Mimics galactosemia; triggered by breast milk, leads to hypoglycemia and jaundice.
- Essential Fructosuria: Fructokinase defect, benign condition.
- Galactosemia: Accumulates galactose-1-phosphate, usually diagnosed in early infancy, requiring dietary restrictions.
TCA Cycle
- Inhibitors: Fluoroacetate, arsenate, and malonate affect key enzymes.
- Produces up to 10 ATP from one cycle; FADH2 is generated by succinate dehydrogenase.
- Anaplerotic reactions, especially by pyruvate carboxylase, maintain TCA cycle intermediates.
- Key vitamins needed: Pantothenic acid (CoA), thiamine (α-KG), involved in various metabolic pathways.
Urea Cycle
- Carbamoyl phosphate synthetase I is the rate-limiting step, activated by N-acetyl glutamate.
- Involves conversion processes in mitochondria and cytoplasm, with argininosuccinate synthetase and lyase playing critical roles.
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