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: 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 862: A scientist is studying a biochemical reaction that takes place in the liver.
- He cultures hepatocytes with glutamate labeled with nitrogen isotopes.
- After some time, he finds that the nitrogen isotopes are transferred to oxaloacetate, forming aspartate.
- Which vitamin is most likely involved in this reaction?
Answer: Vitamin B6 (Pyridoxine)
Extra: This is a **transamination** reaction catalyzed by **Aspartate Aminotransferase (AST)**.
All transamination reactions require **Pyridoxal Phosphate (PLP)**, the active form of **Vitamin B6**, as a cofactor.
In this reaction, the amino group from glutamate is transferred to the alpha-keto acid oxaloacetate to form aspartate and alpha-ketoglutarate.
Flashcard 863: What are the roles of the following enzymes in catecholamine metabolism?
- Catechol-O-methyltransferase (COMT)
- Monoamine oxidase (MAO)
- Phenylethanolamine-N-methyltransferase (PNMT)
Answer: • **COMT & MAO**: Involved in the **degradation** (breakdown) of catecholamines.
• **PNMT**: Involved in the **synthesis** of epinephrine (converts Norepinephrine to Epinephrine).
Flashcard 864: A deficiency of the following enzymes will lead to what disease?
-Delta- aminolevulinate dehydratase
-Delta-aminolevulinate synthase
-Cystathionine synthase
-Glucose-6-phosphate dehydrogenase
-Pyruvate kinase
Answer: D ALA dehydratase: Lead poisoning
-D ALA synthase: Sideroblastic anemia
-Cystathione synthase: usually convert homocystine to cystathionine (with help of B6), thus lead to homocystinuria.
-G6PD: hemolytic anemia
-Pyruvate kinase: (autosomal recessive disease) Hemolytic anemia.
Flashcard 865: 6 month old full term boy comes with lethargy and vomiting.
-Patient was breastfed exclusively until 2 days ago when homemade purred food was added to his diet.
-Serum glucose: 30 mg/dL.
-Dx: confirms aldolase B deficiency.
What should be removed from this patient's diet?
Answer: Sucrose or fructose
due to aldolase B deficiency
(sucrose: glucose+fructose) fructose --> fructose 1 phosphate by fructokinase. Fructose 1-phosphate ---> glyceraldehyde by aldolase B.
Aldolase B deficiency: Fructose intolerence
Fructokinase defect or deficiency: Essential fructosuria
Flashcard 866: 18 y/o girl with type 1 DM comes with several hours of nausea, vomiting and abdominal pain.
- Breath: fruity odor
- Glucose: 452 mg/dL & high anion gap metabolic acidosis.
- Increased activity of what enzyme is most likely contributing to this patient's abnormal blood glucose finding?
Answer: Glycerol kinase
It converts glycerol (released from adipose tissue during lipolysis) into glycerol 3-phosphate in the liver, which is then used as a substrate for gluconeogenesis.
Flashcard 867: What is the status/relevance of the following enzymes in **Lesch-Nyhan syndrome**?
- Aspartate carbamoyltransferase
- Dihydroorotase
- Hypoxanthine-guanine phosphoribosyltransferase (HGPRT)
- PRPP amidotransferase (Phosphoribosyl pyrophosphate amidotransferase)
- Ribonucleotide reductase
- Thymidylate synthase
Answer: - **HGPRT**: **Deficient/Absent** (this is the primary genetic defect).
- **PRPP amidotransferase**: **Activity increases** (due to elevated PRPP levels and decreased feedback inhibition, resulting in increased *de novo* purine synthesis).
- **Aspartate carbamoyltransferase, Dihydroorotase, and Thymidylate synthase**: **Unaffected** (these are enzymes of pyrimidine synthesis).
- **Ribonucleotide reductase**: **Unaffected** (converts ribonucleotides to deoxyribonucleotides for both purines and pyrimidines).
Extra: Lesch-Nyhan syndrome is an X-linked recessive disorder characterized by HGPRT deficiency. This leads to:
1. Failure of the purine salvage pathway (Hypoxanthine/Guanine -> IMP/GMP).
2. Accumulation of PRPP (which is not consumed by the salvage pathway).
3. Increased *de novo* purine synthesis (because PRPP is a potent activator of PRPP amidotransferase, the rate-limiting enzyme of the de novo pathway).
4. Excess uric acid production (hyperuricemia) and characteristic behavioral symptoms like self-mutilation.
Flashcard 868: Coproporphyrinogen III is converted to _____ (heme synthesis)
Answer: Protoporphyrinogen IX
Flashcard 869: What peptide is packaged with insulin and may be used to monitor beta cell function in patients receiving exogenous insulin?_____
Answer: C peptide (connecting peptide)
Flashcard 870: What is the mode of inheritance of maple syrup urine disease?_____
Answer: Autosomal recessive
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