Metabolism — Flashcards

Flashcard 831: A 34-year-old man presents with a facial injury. - He reports getting hit on the face during a fistfight. - Physical exam: Dark blue periorbital ecchymosis on the right side. - Ophthalmic & neurologic examinations are otherwise normal. - The patient is discharged home, but several days later the bruise becomes greenish in color. - This change in color is best explained by the activity of which enzyme?

Answer: Heme oxygenase A bruise (ecchymosis) changes color as hemoglobin is degraded: 1. Heme (purple/blue) is converted to Biliverdin (green) by **Heme oxygenase**. 2. Biliverdin is then converted to Bilirubin (yellow) by **Biliverdin reductase**.

Flashcard 832: In what disease should the followings be restricted? -Galactose -Leucine -Methionine -Phenylalanine -Tyrosine

Answer: Galactose: galactosemia (due to deficiency of Galactose-1-phosphate uridyl transferase) (GALT def.) -Leucine: Maple syrup disease, due to deficiency of branched chain a-ketacid dehydrogenase. -Methionine: should be restricted in homocysteinuria,because methionine converts to homocystein. Instead you will want to give B12 (cobalamine) to convert to methionine & B6 (pyridoxine) to convert to cysteine to relieve the high level of homocysteine. -Phenylalanine: Phenylketonuria (def. of phenyl hydroxylase), musty odor, neurological symptoms. -Tyrosine: restricted in hypertyrosinemia (progressive liver & renal disease) or in alkaptonuria (homogentisate oxidase def.) (black urine on air, black cartillage).

Flashcard 833: What are the following enzymes associated with? - Acetyl CoA carboxylase - Acyl CoA synthetase - ATP citrate lyase - Glucose-6-phosphate dehydrogenase - Glycerol kinase

Answer: - Acetyl CoA carboxylase: Conversion of acetyl-CoA to malonyl-CoA in fatty acid synthesis (Biotin/B7 cofactor). - Acyl CoA synthetase: Activation of fatty acids for breakdown; forms acyl-CoA which then enters mitochondria via the carnitine shuttle. - ATP citrate lyase: Conversion of citrate to acetyl-CoA in the cytosol for fatty acid synthesis. - G6PD: Pentose phosphate pathway; provides NADPH and ribose (nucleotide synthesis). - Glycerol kinase: Phosphorylation of glycerol for conversion into glucose (gluconeogenesis) or triglycerides.

Flashcard 834: A newborn presents with lethargy, vomiting, and hypotonia during the first few days of life. - Lab: metabolic acidosis with large anion gap, ketosis, & hypoglycemia. - Concentration of propionic acid is increased in the plasma and urine. - Metabolism of which amino acids contributes to this patient's condition?

Answer: Valine, Isoleucine, Methionine, and Threonine (Mnemonic: VOMIT — Valine, Odd-chain fatty acids, Methionine, Isoleucine, Threonine) This patient has Propionic Acidemia, caused by a deficiency of propionyl-CoA carboxylase (requires Biotin/B7 as a cofactor). This enzyme normally converts propionyl-CoA to methylmalonyl-CoA. Accumulation of propionic acid leads to metabolic acidosis, ketosis, and hypoglycemia.

Flashcard 835: A researcher develops an agent that specifically blocks the interaction of inositol triphosphate (IP3) with its intracellular receptor. Compared to control cells, decreased activity of which enzyme is most likely to be observed in the experimental cells?

Answer: Protein Kinase C (PKC) IP3 binds to receptors on the smooth endoplasmic reticulum to release intracellular calcium (Ca2+). Both Ca2+ and DAG are required to activate Protein Kinase C.

Flashcard 836: A researcher is investigating the relationship between insulin concentration and the number of glucose transporters on the cell surface. - **Circles**: Surface transporter count increases as insulin concentration rises. - **Triangles**: Surface transporter count remains constant regardless of insulin concentration. Which cell types are most likely represented by the circles and triangles?

Answer: **Circles**: Skeletal muscle or Adipocytes (Insulin-dependent; uses **GLUT4**) **Triangles**: Most other cells (Insulin-independent; e.g., Liver, Brain, RBCs, Kidney)

Extra: Insulin-dependent glucose uptake occurs in skeletal muscle and adipose tissue via **GLUT4**. In the absence of insulin, GLUT4 is sequestered in intracellular vesicles. Insulin signaling triggers the translocation of these vesicles to the plasma membrane. Most other tissues (Liver, RBCs, Brain, Kidney) use insulin-independent transporters (GLUT1, 2, 3, or 5) which are constitutively present on the cell surface.

Flashcard 837: 78 y/o woman presents with tenderness and easy bleeding of the gums when brushing her teeth. - Physical exam: swollen gingiva that bleed on probing. - Skin: perifollicular hemorrhages and petechiae are noted. Her symptoms are most likely caused by hypoactivity of an enzyme found in which cellular compartment?

Answer: Rough endoplasmic reticulum (RER) This is where Vitamin C-dependent hydroxylation of proline and lysine residues (on procollagen chains) occurs. Deficiency leads to scurvy.

Flashcard 838: 22 y/o man comes with recurrent blistering on the back of his hands and forarms for the past several years. -He has used overcounter meds, but symptoms didn't improve. -He has no exposure to chemicals or animals -Physical exam: vesicles and erosions on the dorsum of both hands. -Which enzymes is most likely deficient in this patient in relation to heme synthesis pathway?

Answer: Uroporphyrinogen decarboxylase because patient present with skin blistering (photosensitivity) due to Porphyria cutanea tarda (PCT)

Flashcard 839: A 17 y/o boy with type 1 diabetes mellitus is found unresponsive at home. - Glucose fingerstick: 32 mg/dL - Paramedics administer an injection. - The injected substance binds to a transmembrane receptor in hepatocytes, which promotes binding of intracellular GTP to a specific receptor-associated protein. - This leads to the rapid release of glucose into the blood. Which of the following is the most likely mediator responsible for these effects? a.) cGMP dependent protein kinase b.) Janus tyrosine kinase c.) phosphodiesterase d.) Protein kinase A e.) Tyrosine specific protein kinase

Answer: d.) Protein kinase A Glucagon binds to Gs-protein coupled receptors on hepatocytes, activating adenylyl cyclase to increase cAMP levels. cAMP then activates **Protein Kinase A (PKA)**, which triggers glycogenolysis.

Flashcard 840: A healthy 34-year-old worker is trapped underground following the partial collapse of an access shaft. It takes 2 days to reach him. He has not eaten for over 30 hours. Fingerstick blood glucose concentration is 78 mg/dL. Which biochemical reactions are most likely responsible for maintaining this patient's current blood glucose levels?

Answer: Pyruvate → Oxaloacetate → Phosphoenolpyruvate (Gluconeogenesis)