HNF 462 1st Edition Lecture 25Outline of Last LectureI. Functions of ZincII. Zinc-Dependent Enzymes and Transcriptional FactorsIII. Zn Finger ProteinsIV. Zinc DeficiencyV. Development of Immune CellsVI. Reprogramming Under Zinc DeficiencyOutline of Current LectureI. SourcesII. Digestion, Absorption, Transport, and StorageIII. MetabolismIV. Selenoproteinsa. Glutathione Peroxidase (GPX)b. Thioredoxin ReductaseCurrent Lecture: Selenium (Se) Pt 11. Sourcesa. Organic Formsi. Selenomethionine: Plantsii. Selenocysteine: Meatb. Inorganic Formsi. Selenate2. Digestion, Absorption, Transport, and Storagea. Digestion/Absorptioni. Inorganic Forms1. Absorbed throughout small intestine, not regulatedThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.2. Enhancers: Vitamins C, A, and E; reduced glutathione3. Inhibitors: Heavy metals and phytic acidii. Organic Forms1. Absorbed in similar mechanisms to proteinsb. Transporti. Selenoamino acids transported using same transporters as amino acidsii. Selenium salts travel freely in the bloodc. Storagei. High concentrations in thyroid gland, kidney, heart, pancreas, and muscleii. Also stored in lungs, brain, bone, and RBCs3. Metabolisma. Selenomethionine (from food) selenocysteine: metabolized very similarly to methioninei. Selenocysteine can also come directly from foodb. Selenocysteine metabolized to selenide (reduced form of Se)i. Selenide is excreted by methylation when excess Se is in the body: excreted through urine, feces, and breath (less important pathway)ii. Synthesis of Se-containing proteins: Selenocysteine is the “21st amino acid”1. Selenocysteine has own codon (UEA—normally a stop codon) and its own tRNA for transportation2. tRNA attaches to Ser residue3. Selenide selenophosphate by SPS2 enzyme4. SelA enzyme combines Ser residue and selenophosphate to make selenocysteine5. Attachment to elongating protein chain: SECIS binds to SBP2 protein, then recruits SelB6. SelB grabs selenocysteine from tRNA and inserts it into protein structure7. Cells don’t use selenocysteine directly to make proteins; insertion is very well controlled (this is the same for selenomethionine)4. Selenoproteins: 20-30 discovered in the human bodya. Glutathione Peroxidase (GPX): antioxidanti. Involved in redox homeostasisb. Thioredoxin Reductase: antioxidanti. Involved in the formation of DNAii. rNDP reductase removes oxygen, which results in oxidation of enzymeiii. To recycle rNDP reductase, thioredoxin is needed (results in oxidation of thioredoxin)iv. Thioredoxin Reductase converts back to reduced form so the cycle can continuec. Selenophosphate Synthetase 2: Selenoprotein synthesisd. Selenoprotein P: antioxidant, selenium transporte. Iodothyronine 5’-Deiodinases (IDI or DI): T4T3f. Methionine R Sulfoxide Reductase:
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