Metabolism — Flashcards

Flashcard 791: In which diseases would a deficiency of these enzymes present? - Acid α-glucosidase - Aldolase B - Fructokinase - Galactose-1-phosphate uridyl transferase - Lactase

Answer: - **Acid α-glucosidase**: Pompe disease (GSD type II) - **Aldolase B**: Hereditary fructose intolerance - **Fructokinase**: Essential fructosuria - **Galactose-1-phosphate uridyl transferase**: Classic galactosemia - **Lactase**: Lactose intolerance

Extra: - **Pompe disease**: Lysosomal acid maltase deficiency. Characterized by cardiomegaly, hypertrophic cardiomyopathy, exercise intolerance, and systemic findings leading to early death. - **Hereditary fructose intolerance**: Deficiency of Aldolase B leads to accumulation of fructose-1-phosphate; presents with hypoglycemia, jaundice, and cirrhosis after ingestion of fructose, sucrose, or sorbitol. - **Essential fructosuria**: Deficiency of fructokinase; a benign, asymptomatic condition where fructose appears in blood and urine. - **Classic galactosemia**: Deficiency of GALT. Presents with failure to thrive, jaundice, hepatomegaly, infantile cataracts, and intellectual disability. - **Lactose intolerance**: Deficiency of lactase results in osmotic diarrhea, bloating, and flatulence after dairy consumption.

Flashcard 792: What are the symptoms of deficiency of the following vitamins and substances? - Ascorbic acid - Biotin - Linoleic acid - Vitamin K - Zinc

Answer: - Ascorbic acid: Scurvy, impaired wound healing, bleeding (e.g., petechiae, ecchymoses). - Biotin: Vitamin B7; neuropsychiatric symptoms, alopecia (hair loss), and dermatitis. - Linoleic acid: Essential fatty acid; growth retardation and skin changes. - Vitamin K: Bleeding diathesis (increased PT/INR). - Zinc: Growth retardation, infertility, acrodermatitis enteropathica, and impaired wound healing.

Flashcard 793: A newborn presents with lethargy, vomiting, and hypotonia during the first few days of life. - Lab: metabolic acidosis with large anion gap, ketosis, & hypoglycemia. - Concentration of propionic acid is increased in the plasma and urine. - Metabolism of which amino acids contributes to this patient's condition?

Answer: Valine, Isoleucine, Methionine, and Threonine (Mnemonic: VOMIT — Valine, Odd-chain fatty acids, Methionine, Isoleucine, Threonine) This patient has Propionic Acidemia, caused by a deficiency of propionyl-CoA carboxylase (requires Biotin/B7 as a cofactor). This enzyme normally converts propionyl-CoA to methylmalonyl-CoA. Accumulation of propionic acid leads to metabolic acidosis, ketosis, and hypoglycemia.

Flashcard 794: 22 y/o comes with 5 day history of Nausea, constipation, and severe, poorly localized abdominal pain. -She also reports anxiety, poor sleep quality and tingling of limbs. -She doesn't take any drugs,no smoking, medication or use alcohol. -Patient receives intravenous infusion of heme preparation that leads to rapid resolution of her symptoms. -The improvement in symptoms is most likely due to treatment-induced downregulation of what enzymes?

Answer: Aminolevulinate synthase (ALA Synthase) which is the rate limiting step in heme synthesis. Patient has Acute intermittent porphyria (recurrent abdominal pain, neuropsychosis symptoms) Symptoms: 5 P's: Port wine urine, polyneuropathy, painful abdomen, psychosis, precipitated by drugs (cytochrome p450) Glucose or heme makes better. (inhibits ALA synthase)

Flashcard 795: A researcher develops an agent that specifically blocks the interaction of inositol triphosphate (IP3) with its intracellular receptor. Compared to control cells, decreased activity of which enzyme is most likely to be observed in the experimental cells?

Answer: Protein Kinase C (PKC) IP3 binds to receptors on the smooth endoplasmic reticulum to release intracellular calcium (Ca2+). Both Ca2+ and DAG are required to activate Protein Kinase C.

Flashcard 796: What are the followings in relation to gluconeogenesis? -Acetyl CoA -Alanine -Citrate -Fructose 2,6-bisphosphate -Lactate -Oxaloacetate

Answer: - **Acetyl-CoA**: Obligate activator of **pyruvate carboxylase**, shunting pyruvate toward gluconeogenesis. - **Alanine**: Major gluconeogenic amino acid; also **inhibits pyruvate kinase** to prevent glycolysis. - **Citrate**: **Inhibits PFK-1**, which slows glycolysis and favors gluconeogenesis. - **Fructose 2,6-bisphosphate**: Potent inhibitor of gluconeogenesis; **low levels** are necessary for gluconeogenesis to occur. - **Lactate**: Precursor produced in muscles and red blood cells; converted to glucose in the liver (**Cori cycle**). - **Oxaloacetate**: First intermediate of gluconeogenesis; must be shuttled from the mitochondria to the cytosol (via the malate shuttle) to continue the pathway.

Flashcard 797: Describe the clinical significance or deficiency symptoms associated with the following enzymes: A) Lactase B) Aldose reductase (in the context of galactose metabolism) C) Galactokinase D) Galactose-1-phosphate uridyltransferase (GALT) E) Phosphoglucoisomerase

Answer: A.) **Lactase**: Deficiency leads to **lactose intolerance** (bloating, cramps, osmotic diarrhea). Primarily occurs in adults; congenital form is very rare. B.) **Aldose reductase**: Converts galactose to **galactitol**. In GALK or GALT deficiency, galactose levels rise and are shunted to this pathway, causing galactitol accumulation in the lens and **cataracts**. C.) **Galactokinase (GALK)**: Deficiency leads to high galactose and galactitol, resulting in **infantile cataracts**, galactosemia, and galactosuria. D.) **Galactose-1-phosphate uridyltransferase (GALT)**: Deficiency causes **classic galactosemia**. Presents in neonates with vomiting, jaundice, hepatomegaly, cataracts, intellectual disability, and **E. coli sepsis**. E.) **Phosphoglucoisomerase**: Deficiency causes **hereditary non-spherocytic hemolytic anemia** due to a block in glycolysis.

Flashcard 798: A group of investigators is studying the regulation of catecholamines synthesis in response to severe stress. -The experimental animals are found subsequently to have decreased production of epinephrine by the adrenal medulla compared with the control animals. -Decreased activity of which enzymes is most likely responsible for the observed effect?

Answer: Phenylethanolamine-N-methyltransferase (PNMT) wihch usually stimulated by cortisol converted NE to Epi.

Flashcard 799: A researcher is investigating the relationship between insulin concentration and the number of glucose transporters on the cell surface. - **Circles**: Surface transporter count increases as insulin concentration rises. - **Triangles**: Surface transporter count remains constant regardless of insulin concentration. Which cell types are most likely represented by the circles and triangles?

Answer: **Circles**: Skeletal muscle or Adipocytes (Insulin-dependent; uses **GLUT4**) **Triangles**: Most other cells (Insulin-independent; e.g., Liver, Brain, RBCs, Kidney)

Extra: Insulin-dependent glucose uptake occurs in skeletal muscle and adipose tissue via **GLUT4**. In the absence of insulin, GLUT4 is sequestered in intracellular vesicles. Insulin signaling triggers the translocation of these vesicles to the plasma membrane. Most other tissues (Liver, RBCs, Brain, Kidney) use insulin-independent transporters (GLUT1, 2, 3, or 5) which are constitutively present on the cell surface.

Flashcard 800: The followings compounds will serve as a precursor to what? -Arginine -Carotene -Cholesterol -Orotic acid -Phenylalanine -Tryptophan

Answer: Arginine: precursor to urea, nitric oxide, ornithine, agmatine, creatine. -Carotene: Precursor to vit. A. -Cholesterol: precursor to steroid hormones. -Orotic acid: Precursor to pyrimidine to synthesize DNA. -Phenylalanine: Precursor to tyrosine to create catecholamines. -Tryptophan: Precursor to Niacin (B3)