Urea cycle — Flashcards

Flashcard 31: What happens to the ornithine that is formed via the breakdown of arginine (urea cycle)? _____

Answer: It is recycled

Extra:    https://onlinemeded.org/spa/dna-to-protein/amino-acids/acquire?ref=anki 

Flashcard 32: Ornithine transcarbamylase (OTC) deficiency presents with _____ BUN

Answer: decreased

Extra:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/hematology-and-oncology/videos/macrocytic-anemia?index=6] https://onlinemeded.org/spa/metabolism/urea-cycle/acquire?ref=anki 

Flashcard 33: What is the most common urea cycle disorder? _____

Answer: Ornithine transcarbamylase (OTC) deficiency

Extra:   Watch associated Bootcamp video [https://app.bootcamp.com/med-school/hematology-and-oncology/videos/macrocytic-anemia?index=6] https://onlinemeded.org/spa/dna-to-protein/amino-acids/acquire?ref=anki 

Flashcard 34: Ornithine transcarbamylase (OTC) deficiency often presents within the first few _____ of life but may present later

Answer: days

Extra:  Watch associated Bootcamp video [https://app.bootcamp.com/med-school/hematology-and-oncology/videos/macrocytic-anemia?index=6] https://onlinemeded.org/spa/dna-to-protein/amino-acids/acquire?ref=anki 

Flashcard 35: Urea has two nitrogen atoms, one from _____ and one from aspartate

Answer: NH3

Extra: The carbon atom in urea comes from CO2 (bicarbonate).

Flashcard 36: What is the rate-limiting enzyme of the urea cycle? _____

Answer: Carbamoyl phosphate synthetase I

Extra:    https://onlinemeded.org/spa/dna-to-protein/amino-acids/acquire?ref=anki 

Flashcard 37: In the liver, _____ may transfer a molecule of NH3 to the urea cycle, reforming α-ketoglutarate

Answer: glutamate

Extra:   Watch Cahill Cori Cycles [https://dashboard.sketchy.com/study/medical/courses/medical-biochemistry/units/medical-biochemistry-metabolism/videos/medical-biochemistry-metabolism-amino-acids-and-proteins-the-cahill-and-cori-cycles?utm_source=anki&utm_medium=partnership&utm_campaign=february_update&utm_content=medical] https://onlinemeded.org/spa/dna-to-protein/amino-acids/acquire?ref=anki 

Flashcard 38: Does glutamine cause a change in blood pH? _____

Answer: No

Extra:   https://onlinemeded.org/spa/metabolism?ref=anki 

Flashcard 39: Evaluate the following enzyme deficiencies in relation to **high circulating ammonia (NH3)** and **increased orotic acid** in the urine: - Carbamoyl phosphate synthetase 1 (CPS1) - Hypoxanthine-guanine phosphoribosyltransferase (HGPRT) - N-acetylglutamate synthetase (NAGS) - Ornithine transcarbamylase (OTC) - Uridine monophosphate (UMP) synthase

Answer: **Ornithine transcarbamylase (OTC) deficiency** is the only one with both findings. - **CPS1 deficiency**: ↑ NH3, but **low** orotic acid (due to low carbamoyl phosphate). - **NAGS deficiency**: ↑ NH3, but **low** orotic acid (due to low carbamoyl phosphate). - **OTC deficiency**: ↑ NH3 and **high** orotic acid (excess carbamoyl phosphate is shunted into the pyrimidine synthesis pathway). - **UMP synthase deficiency**: **High** orotic acid, but **normal NH3** (it is part of pyrimidine synthesis, not the urea cycle). - **HGPRT deficiency**: High uric acid (Lesch-Nyhan syndrome); does not primarily affect NH3 or orotic acid levels.

Flashcard 40: A 2 y/o boy comes with fever, vomiting and sleepiness. - He had several episodes of emesis this morning. -Prior lab testing: Increased blood ammonia levels during these  episodes, & increased orotic acid excretion in urine. -Physical exam: Tachypneic boy who is unresponsive to all stimuli. -Which enzymes is most likely to be deficient in this patient?

Answer: Ornithine transcarbamylase (OTC) due to OTC deficiency which present with high ammonia which causes comma & tachypnea, excess carbamoyl phosphate, which stimulate pyrimidine synthesis. Increased urinary orotic acid.