Metabolism — Flashcards

Flashcard 811: In which reactions or pathways do the following enzymes occur? - Aconitase - Enolase - Glucose-6-phosphate dehydrogenase (G6PD) - Glutathione reductase - Transketolase

Answer: Aconitase: Citric acid cycle; catalyzes isomerization of citrate to isocitrate. - Enolase: Glycolysis. - G6PD: Pentose phosphate pathway (1st step); irreversible. Deficiency causes hemolytic anemia. - Glutathione reductase: Aids RBCs in resisting oxidative stress (reduces glutathione). - Transketolase: Pentose phosphate pathway; reversible. Can convert ribose-5-phosphate to fructose-6-phosphate. Requires thiamine (B1) as a cofactor.

Flashcard 812: Which hormones are associated with each of the following signaling pathways? - Binding of activated receptors to DNA to modify transcription - Cyclic AMP-Protein kinase A pathway - Diacylglycerol-Protein kinase C pathway - Inositol triphosphate-calcium-calmodulin pathway - Jak-STAT pathway

Answer: - Binding of activated receptors to DNA: (Intracellular receptors) Steroids and thyroid hormones (cortisol, T3/T4, estrogen, vitamin D). - Cyclic AMP-Protein Kinase A pathway: "FLAT ChAMP GCG" (FSH, LH, ACTH, TSH, CRH, hCG, ADH-V2, MSH, PTH, Glucagon, Calcitonin, GHRH). - Diacylglycerol (DAG) & Inositol triphosphate (IP3) pathway: "GOAT HAG" (GnRH, Oxytocin, ADH-V1, TRH, Histamine-H1, Angiotensin II, Gastrin). - Jak-STAT pathway: (Receptor-associated tyrosine kinase) "PiGGLET" (Prolactin, Immunomodulators [cytokines], GH, G-CSF, Erythropoietin, Thrombopoietin).

Flashcard 813: 74 y/o woman comes with 2 days of left leg pain and numbness. - History of A. Fib & hypertension. - Left lower limb is pale & cold to palpation below the knee. - Ultrasound: occluding thrombus & a left femoral embolectomy is performed. - Post procedure dorsalis pedis & posterior tibial pulses become palpable. - Several hours later, patient feels severe left calf pain, with absent distal pulses. - Physician suspects: injury of the reperfused muscles due to overproduction of reactive oxygen species. - Which enzymes are most likely to help neutralize these toxic molecules?

Answer: Superoxide dismutase, Catalase, and Glutathione peroxidase This patient is presenting with **acute compartment syndrome** secondary to **reperfusion injury**. Reperfusion leads to the overproduction of reactive oxygen species (ROS). These molecules are neutralized by antioxidant enzymes: - **Superoxide dismutase** (converts superoxide to hydrogen peroxide) - **Catalase** and **Glutathione peroxidase** (convert hydrogen peroxide to water)

Flashcard 814: Identify the clinical condition or nutrient deficiency associated with each of the following biochemical markers: - Blood protoporphyrin level - Erythrocyte glucose-6-phosphate dehydrogenase (G6PD) activity - Erythrocyte glutathione reductase activity - Erythrocyte transketolase activity - Serum methylmalonic acid level - NADPH

Answer: - **Blood protoporphyrin:** Increased in **Iron deficiency anemia** and **Lead poisoning**. - **Erythrocyte G6PD activity:** Decreased in **G6PD deficiency** (hemolytic anemia). - **Erythrocyte glutathione reductase activity:** Decreased in **Riboflavin (B2)** deficiency (FAD is a cofactor). - **Erythrocyte transketolase activity:** Decreased in **Thiamine (B1)** deficiency (TPP is a cofactor). - **Serum methylmalonic acid:** Increased in **Vitamin B12** deficiency. - **NADPH:** Derived from **Niacin (B3)**; levels reflect B3 status.

Flashcard 815: Which of the following reactions is a step in **gluconeogenesis**? - Acetoacetyl CoA → HMG-CoA - Acetyl CoA → Palmitic acid - Fructose 6-phosphate → Fructose 1,6-bisphosphate - Glycogen → Glucose-1-phosphate - Oxaloacetate → Phosphoenolpyruvate

Answer: Oxaloacetate → Phosphoenolpyruvate **Explanation:** - **Oxaloacetate → Phosphoenolpyruvate**: Catalyzed by PEP carboxykinase (PEPCK); a key regulatory step in **gluconeogenesis**. - **Acetoacetyl CoA → HMG-CoA**: Part of ketogenesis (mitochondria) or cholesterol synthesis (cytosol). - **Acetyl CoA → Palmitic acid**: Part of fatty acid synthesis (lipogenesis), which occurs in the well-fed state. - **Fructose 6-phosphate → Fructose 1,6-bisphosphate**: The rate-limiting step of **glycolysis** (catalyzed by PFK-1). - **Glycogen → Glucose-1-phosphate**: The process of **glycogenolysis**; liver glycogen is typically depleted after 12–24 hours of fasting.

Flashcard 816: What are the following enzymes associated with? - Acetyl CoA carboxylase - Acyl CoA synthetase - ATP citrate lyase - Glucose-6-phosphate dehydrogenase - Glycerol kinase

Answer: - Acetyl CoA carboxylase: Conversion of acetyl-CoA to malonyl-CoA in fatty acid synthesis (Biotin/B7 cofactor). - Acyl CoA synthetase: Activation of fatty acids for breakdown; forms acyl-CoA which then enters mitochondria via the carnitine shuttle. - ATP citrate lyase: Conversion of citrate to acetyl-CoA in the cytosol for fatty acid synthesis. - G6PD: Pentose phosphate pathway; provides NADPH and ribose (nucleotide synthesis). - Glycerol kinase: Phosphorylation of glycerol for conversion into glucose (gluconeogenesis) or triglycerides.

Flashcard 817: A 5 month old boy is brought to the office by his parents concerning that he has development delay. -Physical exam: unable to roll. Does not seem to recognize his parents. -Labs: Impaired tetrahydrobiopterin synthesis. -Which is most likely deficient in this patient?

Answer: Serotonin, Dopamine, and Tyrosine (BH4 is a required cofactor for tryptophan, tyrosine, and phenylalanine hydroxylases).

Flashcard 818: 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 819: 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 820: What are the followings in relation to vitamin deficiency? -Abnormal oxidative decarboxylation of ketoacids. -Abnormal proline hydroxylation -Abnormal transamination -deficient methionine synthesis -Diminished synthesis of purines

Answer: Abnormal oxidative decarboxylation: Thiamine (B1) deficiency -Abnormal proline hydroxylation: vit. C deficiency -Abnormal transamination: Vit. B6 (pyridoxine) deficiency -Deficient methionine synthesis: Vit. B12 (cobalamine) deficiency. -Diminished synthesis of purines: Vit B9 (folate) deficiency