Amino acid metabolism and disorders — Flashcards

Flashcard 41: What is the usual amino acid pattern of collagen?

Answer: Gly-X-Y where X and Y are proline or lysine

Flashcard 42: Where does the cross-linking step of collagen synthesis occur?

Answer: extracellular space

Flashcard 43: Where does the proteolytic processing step of collagen synthesis occur?

Answer: extracellular space

Flashcard 44: Where does the hydroxylation step of collagen synthesis occur?

Answer: ER

Flashcard 45: What is the function of the proteasome?

Answer: degrades proteins tagged with ubiquitin

Flashcard 46: What are the key features and enzyme deficiency in hereditary orotic aciduria?

Answer: Enzyme deficiency: UMP synthase Clinical: Megaloblastic anemia (unresponsive to B12/folate), orotic aciduria, no hyperammonemia. Treatment: Oral uridine.

Extra: Pathophysiology: Inability to convert orotic acid to UMP due to UMP synthase deficiency (bifunctional enzyme: orotate phosphoribosyltransferase and orotidine-5'-phosphate decarboxylase). Inheritance: Autosomal Recessive (AR). Key Differentiator: Unlike Ornithine Transcarbamylase (OTC) deficiency, there is NO hyperammonemia here.

Flashcard 47: Which amino acids are necessary for de novo pyrimidine synthesis?

Answer: Aspartate and Glutamine

Extra: - Pyrimidines: Aspartate, Glutamine (plus CO2). - Purines: Glycine, Aspartate, Glutamine (GAG).

Flashcard 48: Which amino acids are necessary for de novo purine synthesis?

Answer: Glycine, Aspartate, Glutamaine mnemonic: GAG

Flashcard 49: Consequence of Adenosine Deaminase (ADA) deficiency?

Answer: Severe Combined Immunodeficiency (SCID) due to dATP buildup and lymphocyte toxicity.

Extra: • Inheritance: Autosomal Recessive (AR) • Enzyme: Adenosine deaminase (ADA) • Mechanism: dATP accumulates → inhibits ribonucleotide reductase → decreased DNA synthesis → lymphotoxicity. • Presentation: Recurrent infections in infancy, leukopenia. • Treatment: Bone marrow transplant, enzyme replacement, gene therapy.