Metabolism US Medical PG Flashcards - Medical Study Cards
Master Metabolism with OnCourse flashcards. These spaced repetition flashcards are designed for medical students preparing for NEET PG, USMLE Step 1, USMLE Step 2, MBBS exams, and other medical licensing examinations.
Metabolism Flashcard Deck - 10 Cards
Flashcard 861: A 36 y/o man comes with dark urine and back pain.
-patient ate some large, flat beans brought home by his wife after a business trip to egypt.
-Physical exam: Jaundice & pallor.
-Labs: hemoglobin 8g/dL.
-Further evaluation reveals deficiency of an enzyme involved in the conversion of glucose-6-phosphate to ribulose-5-phosphate.
-The substance generated during this conversion is necessary for which biochemical processes?
Answer: NADPH; used in fatty acid synthesis, steroid synthesis, and glutathione reduction.
Diagnosis: Glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Flashcard 862: A 6-month-old boy is brought to the office because he is not developing normally.
- Physical exam: delayed developmental milestones and hypotonia.
- He has a tendency to aggressively bite his own lips and fingers.
- Labs: Elevated blood uric acid level.
Activity of what enzyme is most likely increased in this patient?
Answer: PRPP amidotransferase (Glutamine-phosphoribosyl amidotransferase)
This patient has **Lesch-Nyhan syndrome**, which is caused by a deficiency of **HGPRT**.
In HGPRT deficiency, the activity of **PRPP amidotransferase** (the rate-limiting enzyme of *de novo* purine synthesis) increases due to:
1. Increased availability of **PRPP** (substrate).
2. Decreased levels of **IMP** and **GMP** (loss of feedback inhibition).
**HGPRT** mnemonic:
**H**yperuricemia
**G**out
**P**issed off (aggression/self-mutilation)
**R**etardation
dys**T**onia (and choreoathetosis)
Flashcard 863: In what reactions do the following amino acids participate?
- Phenylalanine
- Valine
- Asparagine
- Histidine
- Proline
- Lysine
Answer: - **Phenylalanine**: Converted to tyrosine by **phenylalanine hydroxylase**. Deficiency of this enzyme leads to PKU.
- **Valine**: Part of the "VOMIT" pathway (Valine, Odd-chain fatty acids, Methionine, Isoleucine, Threonine); these synthesize **propionyl-CoA**, which converts to methylmalonyl-CoA (via propionyl-CoA carboxylase) and then to **succinyl-CoA** (via methylmalonyl-CoA mutase).
- **Asparagine**: Converted to aspartate by **asparaginase**. Leukemic cells require asparagine for survival, so L-asparaginase is used as an antineoplastic agent.
- **Histidine**: Converted to **histamine** (via histidine decarboxylase), which is released by mast cells in Type 1 hypersensitivity and stimulates gastric acid secretion.
- **Proline**: Converted to **glutamate**, which can then be converted to $\alpha$-ketoglutarate. It is also **hydroxylated** by Vitamin C during collagen synthesis.
- **Lysine**: Strictly **ketogenic**. Like proline, it is **hydroxylated** by Vitamin C during collagen synthesis.
Flashcard 864: What is the clinical or metabolic significance of the following enzymes?
- Bisphosphoglycerate mutase
- Hexokinase
- Pyruvate kinase
- Transketolase
Answer: • Bisphosphoglycerate mutase: Synthesizes 2,3-BPG in RBCs (Rapoport-Luebering shunt), which decreases Hb affinity for O2 and facilitates oxygen unloading to tissues.
• Hexokinase & Pyruvate kinase: Glycolytic enzymes; deficiency leads to hemolytic anemia.
• Transketolase: Pentose Phosphate Pathway enzyme that requires thiamine (B1) as a cofactor. It converts ribose-5-phosphate to fructose-6-phosphate. RBC transketolase activity is decreased in thiamine deficiency.
Flashcard 865: A 2 y/o boy comes to the office by his parents because they notice the boy urine turned black overnight.
-Child has no significant past medical history, no medications.
-Physical exam: well-nourished child with no swelllin or tenderness of any joints.
-Urinalysis: Black urine
-Which of the following conversion pathway is most likely deficient in this patient?
Answer: Tyrosine to fumarate
due to deficiency of homogentisate dioxigenase enzymes, which cause accumulation of homogentisate. (Alkaptonuria)
Flashcard 866: 12 y/o patient presents with severe chest pain.
- He has had intermittent substernal chest pain for the past few months, occurring after heavy activity.
- BP: 130/80 Pulse: 132/min RR: 24/min
- Physical exam: Anxious appearing boy with rapid but regular pulse.
- Troponin is elevated. ECG reveals ST segment elevations in leads II, III, & aVF.
- Further lab results: Increased serum methionine level.
- Which amino acid is most likely essential in this patient?
Answer: Cysteine
Due to homocystinuria, which leads to premature thromboembolic events such as atherosclerosis and acute coronary syndrome.
Flashcard 867: A 6 month old girl comes with mother due to lack of growth despite feeding.
-Physical exam: Hepatomegaly, hypotonia, height & weight below the 10th percentile.
-Lab: Hypoglycemia, ketoacidosis
-Liver biopsy: hepatic fibrosis without fat accumulation.
-Which enzymes is most likely deficient in this patient?
Answer: Debranching enzyme (alpha 1,6-glucosidase)
due to Cori disease.
Present with Hepatomegaly, hypoglycemia, hypotonia without cardiomegaly.
Flashcard 868: What are the following substances? What happens due to deficiency of these substances?
- Folic acid
- Tocopherol
- Riboflavin
- Pyridoxine
Answer: - **Folic acid**: Vitamin B9; deficiency leads to megaloblastic anemia.
- **Tocopherol**: Vitamin E; fat-soluble antioxidant; deficiency leads to hemolytic anemia and neurological symptoms (ataxia, loss of proprioception/vibration).
- **Riboflavin**: Vitamin B2; precursor for FAD and FMN; deficiency leads to cheilosis (cracks/scaling at corners of mouth), glossitis, and corneal vascularization/keratitis.
- **Pyridoxine**: Vitamin B6; deficiency leads to peripheral neuropathy, sideroblastic anemia, and homocysteinuria.
Flashcard 869: Metabolism of _____ ultimately produces uric acid
Answer: purines
Flashcard 870: Which classes (2) of steroid hormones are decreased in 21-hydroxylase deficiency?_____
Answer: glucocorticoids and mineralocorticoids
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