Metabolism — Flashcards

Flashcard 801: 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 802: 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 803: 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 804: 3 day old boy comes with poor feeding, vomiting, and progressive lethargy. -Parents stated: "Diaper have burnt sugar smell" -Physical Exam: Lethargic infant with dry mucous membranes and generalized hypertonia. -Which of the following should be restricted from this infant's diet?

Answer: Leucine or VAL: Valine, Leucine, Isoleucine Due to Maple syrup urine disease, caused by a deficiency of branched chain a-ketoacid dehydrogenase thus can't metabolize VAL.

Flashcard 805: What are the followings in relation to phosphorylation of mannose residues on glycoproteins? -Extracellular space -Lysosome -Mitochondria -Nucleus -Plasma membrane

Answer: Extracellular space: doesn't need phosphorylation of mannose residues on proteins. They will just packed in a vesicles which fuse with plasma membrane to release extracellular proteins. -Lysosome: does require phosphorylation of mannose residues on glycoproteins in order for them to enter the lysosome. Will help with degradation. -Mitochondria: They don't need protein phosphorylation. Most mitochondrial proteins will synthesize in the cytosol. -Nucleus: Protein will present with a nuclear signals (nuclear localization signals) to import or enter the nucleus. -Plasma membrane: Protein will covalently bind to an hydrophobic lipid anchor that will facilitate protein interaction with cell membrane.

Flashcard 806: What are the followings in relation to vitamin deficiency? -Abnormal oxidative decarboxylation of ketoacids. -Abnormal proline hydroxylation -Abnormal transamination -deficient methionine synthesis -Diminished synthesis of purines

Answer: Abnormal oxidative decarboxylation: Thiamine (B1) deficiency -Abnormal proline hydroxylation: vit. C deficiency -Abnormal transamination: Vit. B6 (pyridoxine) deficiency -Deficient methionine synthesis: Vit. B12 (cobalamine) deficiency. -Diminished synthesis of purines: Vit B9 (folate) deficiency

Flashcard 807: 6 month old full term boy comes with lethargy and vomiting. -Patient was breastfed exclusively until 2 days ago when homemade purred food was added to his diet. -Serum glucose: 30 mg/dL. -Dx: confirms aldolase B deficiency. What should be removed from this patient's diet?

Answer: Sucrose or fructose due to aldolase B deficiency (sucrose: glucose+fructose) fructose --> fructose 1 phosphate by fructokinase. Fructose 1-phosphate ---> glyceraldehyde by aldolase B. Aldolase B deficiency: Fructose intolerence Fructokinase defect or deficiency: Essential fructosuria

Flashcard 808: 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 809: 24 y/o man comes with episodic anemia, jaundice, & dark urine. - These episodes typically occur after use of certain drugs or following infection. - History: brother has similar episodes. - Peripheral blood smear: shows bite cells and Heinz bodies. Deficiency of what enzyme would most likely result in a condition similar to this patient's presentation?

Answer: Glutathione reductase

Extra: The clinical vignette describes **Glucose-6-phosphate dehydrogenase (G6PD) deficiency** (episodic hemolysis triggered by oxidative stress). **Glutathione reductase** deficiency results in a similar presentation because it is the enzyme responsible for regenerating reduced glutathione (GSH) using NADPH. Without GSH, RBCs cannot neutralize reactive oxygen species, leading to Heinz body formation and bite cells.

Flashcard 810: A deficiency of the following enzymes will lead to what disease? -Delta- aminolevulinate dehydratase -Delta-aminolevulinate synthase -Cystathionine synthase -Glucose-6-phosphate dehydrogenase -Pyruvate kinase

Answer: D ALA dehydratase: Lead poisoning -D ALA synthase: Sideroblastic anemia -Cystathione synthase: usually convert homocystine to cystathionine (with help of B6), thus lead to homocystinuria. -G6PD: hemolytic anemia -Pyruvate kinase: (autosomal recessive disease) Hemolytic anemia.