Metabolism — Flashcards

Flashcard 831: 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)

Flashcard 832: With which signaling pathways are the following events associated (in the context of growth factors and cellular regulation)? - **Ca²⁺ efflux from the endoplasmic reticulum** - **cAMP accumulation** - **Dimerization of STAT proteins** - **Activation of S6 kinase (protein synthesis)** - **Translocation of ERK (MAPK) to the nucleus** (Choices: MAP-kinase pathway, mTOR pathway, Inositol phospholipid pathway, cAMP pathway, JAK/STAT pathway)

Answer: 1. **Inositol phospholipid pathway**: Phospholipase C (PLC) → IP₃ → Ca²⁺ release from the endoplasmic reticulum. 2. **cAMP pathway**: Gs-protein → Adenylate cyclase → ↑cAMP → Protein Kinase A (PKA). 3. **JAK/STAT pathway**: Ligand binding → JAK (non-receptor tyrosine kinase) phosphorylation → STAT dimerization. 4. **mTOR pathway**: Activated downstream of PI3K/Akt; regulates protein synthesis (translation) via **S6 kinase (S6K)** and 4E-BP1. 5. **MAP-kinase pathway**: Growth factor → Ras → Raf → MEK → ERK (MAPK); activated ERK translocates to the nucleus to initiate gene transcription (STAT proteins also translocate to the nucleus).

Extra: **JAK/STAT Pathway Ligands (Mnemonic: PIGGLET):** - **P**: Prolactin - **I**: Immunomodulators (Cytokines: IL-2, IL-6, IFN) - **G**: Growth Hormone (GH) - **G**: G-CSF - **L**: Leptin - **E**: Erythropoietin (EPO) - **T**: Thrombopoietin (TPO) **Note on cGMP:** - **Visual phototransduction**: Light → Transducin → PDE activation → **↓cGMP** (occurs in the retina; classic example of rapid cGMP decrease). - **ANP, BNP, and NO**: Activate Guanylate Cyclase → **↑cGMP** → Vasodilation. - **PDE-5 inhibitors** (e.g., Sildenafil) prevent cGMP breakdown.

Flashcard 833: Molecular biologists studying signal transduction apply an agent to human cells that activates G-protein-dependent phospholipase C. Which intracellular substances are most likely to increase immediately after exposure to this agent?

Answer: IP3, DAG, and Ca2+

Flashcard 834: What are the disacharide breakdown of: -Sucrose -Lactose -Maltose

Answer: Sucrose: Glucose + fructose -Lactose: Glucose + galactose -Maltose: Glucose + Glucose

Flashcard 835: what are the followings in relation to Phenylalanine metabolism? -Dihydrobiopterin reductase -Dopamine B-hydroxylase -Dopamine decarboxylase -Phenylalanine hydroxylase -Phenylethanolamine N-methyltransferase -Tyrosinase

Answer: Dihydrobiopterin reductase: convert BH2 to BH4 in order to use BH4 as a cofactor to convert phenylalanine to tyrosine. -Dopamine B-hydroxylase: convert dopamine to norepinephrine. Requires Vit. C as cofactor. -Dopamine Decarboxylase: convert DOPA to dopamine. Requires Vit. B6 as cofactor. -Phenylalanine hydroxylase: convert phenylalanine to tyrosine. Requires BH4 as cofactor. -Phenylethanolamine N-methyltransferase: convert norepinephrine to epinephrine. Requires SAM as cofactor. -Tyrosinase: convert tyrosine (DOPA to melanin). Tyrosinase deficiency will cause albinism.

Flashcard 836: In which reactions or pathways do the following enzymes occur? - Aconitase - Enolase - Glucose-6-phosphate dehydrogenase (G6PD) - Glutathione reductase - Transketolase

Answer: Aconitase: Citric acid cycle; catalyzes isomerization of citrate to isocitrate. - Enolase: Glycolysis. - G6PD: Pentose phosphate pathway (1st step); irreversible. Deficiency causes hemolytic anemia. - Glutathione reductase: Aids RBCs in resisting oxidative stress (reduces glutathione). - Transketolase: Pentose phosphate pathway; reversible. Can convert ribose-5-phosphate to fructose-6-phosphate. Requires thiamine (B1) as a cofactor.

Flashcard 837: 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 838: 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 839: 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 840: 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.