Metabolism — Flashcards

Flashcard 791: 12 y/o male is evaluated for ataxia accompanied by episodic erythematous and pruritic skin lesions and loose stools. -Labs: Loss of neutral amino acids in the urine. -This patient's symptoms would most likely respond to what supplements?

Answer: Niacin (Vitamin B3) This patient has **Hartnup disease**, which is characterized by a defect in the transporter for **neutral amino acids** (like tryptophan) in the proximal renal tubule and enterocytes. Since tryptophan is a precursor for niacin, deficiency leads to **pellagra**-like symptoms: - Dermatitis - Diarrhea - Dementia (or ataxia in this case)

Flashcard 792: Scientists studying the principles behind oxygen-hemoglobin dissociation separate hemoglobin tetramers into individual subunits. What would the oxygen dissociation curve of isolated beta subunits resemble?

Answer: It will resemble **myoglobin** (a **hyperbolic** curve). Isolated subunits lack the cooperative binding properties of the hemoglobin tetramer and have a significantly higher oxygen affinity.

Extra: Normal adult hemoglobin (HbA) is a tetramer ($\alpha_2\beta_2$) that exhibits **positive cooperativity**, resulting in a **sigmoidal** (S-shaped) oxygen dissociation curve. Individual alpha or beta subunits (or $\beta_4$ tetramers, known as HbH) lack these allosteric interactions and bind oxygen with very high affinity, resulting in a **hyperbolic** curve similar to myoglobin.

Flashcard 793: Identify the disease(s) associated with a deficiency or inhibition of the following enzymes: - Delta-Aminolevulinate dehydratase - Delta-Aminolevulinate synthase - Bilirubin glucuronyl transferase - Porphobilinogen deaminase - Uroporphyrinogen decarboxylase

Answer: - **Delta-Aminolevulinate dehydratase**: Lead poisoning (inhibited by lead) - **Delta-Aminolevulinate synthase**: Sideroblastic anemia (requires Vit B6 as cofactor) - **Bilirubin glucuronyl transferase**: Gilbert syndrome and Crigler-Najjar syndrome - **Porphobilinogen deaminase**: Acute intermittent porphyria (presents with abdominal pain, port-wine urine, and neuropsychiatric issues) - **Uroporphyrinogen decarboxylase**: Porphyria cutanea tarda (presents with photosensitivity and blistering)

Flashcard 794: What are the symptoms of deficiency of the following vitamins and substances? - Ascorbic acid - Biotin - Linoleic acid - Vitamin K - Zinc

Answer: - Ascorbic acid: Scurvy, impaired wound healing, bleeding (e.g., petechiae, ecchymoses). - Biotin: Vitamin B7; neuropsychiatric symptoms, alopecia (hair loss), and dermatitis. - Linoleic acid: Essential fatty acid; growth retardation and skin changes. - Vitamin K: Bleeding diathesis (increased PT/INR). - Zinc: Growth retardation, infertility, acrodermatitis enteropathica, and impaired wound healing.

Flashcard 795: True or False Some patients with porphobilinogen deaminase deficiency could be asymptomatic for Acute intermittent porphyria

Answer: True because porphobilinogen deaminase deficiency is not sufficient enough to cause symptoms.

Flashcard 796: 35 y/o woman comes with nausea, vomiting, and fever. -Her symptoms began 24 hours ago, she's been unable to eat or drink anything since. -Labs: glucose level: 82 mg/dL despite her 24 hour fast. -maintenace of this patient's blood glucose levels is facilitated by hepatic conversion of pyruvate into glucose. -Which of the following substances directly stimulates the 1st enzyme involved in this process?

Answer: Acetyl-CoA It will stimulate Pyruvate carboxylase to convert pyruvate to oxaloacetate. (1st step of gluconeogenesis)

Flashcard 797: 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 798: A 27-year-old woman with acute appendicitis is unable to eat. - Lab: moderate ketones in urine, borderline low serum glucose. - Based on evaluation, it's suspected that this patient is utilizing ketone bodies for energy. - What tissues cannot use this energy source?

Answer: 1. **Erythrocytes** (RBCs): Lack mitochondria (the site of ketone body oxidation). 2. **Liver**: Lacks the enzyme **thiophorase** (succinyl-CoA:3-ketoacid CoA transferase), which is required to activate acetoacetate to acetoacetyl-CoA.

Flashcard 799: A 5-day-old newborn presents with emesis, jaundice, lethargy, and hepatomegaly. Labs show hypoglycemia and elevated transaminases. Blood culture is positive for Gram-negative rods. Which metabolic enzyme is most likely deficient?

Answer: Galactose-1-phosphate uridyltransferase (GALT) :: Classic galactosemia; typically presents with vomiting, jaundice, hepatomegaly, cataracts, and E. coli sepsis.

Flashcard 800: What are the followings in relation to gluconeogenesis? -Glycogen phosphorylase -Hormone sensitive lipase -Lipoprotein lipase

Answer: Glycogen phosphorylase: involved in the break down of glycogen. It is the rate-limiting enzyme in glycogenolysis. Occurs during 1st several hours of fasting. 2 days will most likely be gluconeogenesis. -Hormone sensitive lipase: enzyme found in adipose tissue, will break down tryglycerides into glycerol & free fatty acids--------> leads to glucose & ketone bodies. It depends on stress hormone (catecholamines, glucagon, ACTH) -Lipoprotein lipase: enyzme found in bloodstream will break down tryglycerides found chylomicrons & VLDL and turn them to free fatty acids acids. very similar to hormone sensitive lipase.