Metabolism — Flashcards

Flashcard 821: A 5 month old boy is brought to the office by his parents concerning that he has development delay. -Physical exam: unable to roll. Does not seem to recognize his parents. -Labs: Impaired tetrahydrobiopterin synthesis. -Which is most likely deficient in this patient?

Answer: Serotonin, Dopamine, and Tyrosine (BH4 is a required cofactor for tryptophan, tyrosine, and phenylalanine hydroxylases).

Flashcard 822: What are the following in relation to glycogen storage diseae? -Acid maltase deficiency -Debranching enzymes -Glucose 6-phosphatase -Liver glycogen phosphorylase -Muscle glycogen phosphorylase -Pyruvate kinase

Answer: Acid maltase deficiency: (alpha 1,4 glucosidase), Pompe disease. present with cardiomegaly, hepatomegaly, hypotonia without hypoglycemia, with glycogen storage in lysosome. -Debranching enzymes: (alpha 1,6 glucosidase), Cori disease. Present with hypoglycemia, hypotonia, hepatomegaly. -Glucose 6-phosphatase: Von Gierke disease. Affect mainly liver & kidney. Hepatomegaly, lactic acidosis, hyperuricemia. -Liver glycogen phosphorylase: Hers disease. Present with hypoglycemia, ketosis, & hepatomegaly -Muscle glycogen phosphorylase deficiency: McArdle disease, presents with muscle pain & cramping during excercise, muscle get tired easily during strenuous excercise. -Pyruvate kinase: convert Phosphoenolpyruvate to pyruvate during glycolysis. Will cause chronic hemolytic anemia.

Flashcard 823: 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 824: 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 825: 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 826: 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 827: 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 828: 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 829: 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 830: Identify the required vitamin cofactors for the following metabolic reactions: - Glucose to ribose-5-phosphate - Pyruvate to acetyl-CoA - Pyruvate to alanine - Pyruvate to oxaloacetate - Succinate to oxaloacetate

Answer: - Glucose to ribose-5-phosphate: Niacin (B3) for NADPH production. - Pyruvate to acetyl-CoA: Thiamine (B1), Riboflavin (B2), Niacin (B3), Pantothenic acid (B5), and Lipoic acid (Cofactors for Pyruvate Dehydrogenase). - Pyruvate to alanine: Vitamin B6 (Pyridoxine) for ALT (transamination). - Pyruvate to oxaloacetate: Biotin (B7) for Pyruvate Carboxylase. - Succinate to oxaloacetate: Riboflavin (B2) for Succinate Dehydrogenase (FAD) and Niacin (B3) for Malate Dehydrogenase (NAD+).