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Definition
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Term
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Definition
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Term
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Definition
| M, cys, M, cys, M, P, P, M |
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Term
| Name some enzymes and proteins for which heme is a prosthetic group. (The list is long.) |
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Definition
| Hemoglobin, Myoglobin, Cytrochrome C & P450, Catalase, Ub-cytochrome C Reductase, Cytochrome C Oxidase, Tryptophan pyrolase, Neutrophil NADPH Oxidase, NO Synthase, Cystathionase. |
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Term
| Outline the heme synthesis pathway products. Think about location of products. |
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Definition
| Gly + Succ. CoA --> ALA --> PBG --> 4 bound PBG's --> Uro'gen 1 --> Uro'gen 3 --> Copro'gen 3 --> Proto'gen 9 --> Proto 9 --> Heme. 8 Succinyl CoA molecules and 8 glycines are required. |
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Term
| Outline the heme synthesis pathway enzymes. Think about location of products. |
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Definition
| ALAS (PLP), ALAD, PBG Deaminase, Uro'gen 1 Synthase, Uro'gen 3 Cosynthase, Copro'gen 3 Decarboxylase, Copro'gen 3 oxidase, Proto'gen 9 Oxidase, Ferrochetelase |
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Term
| What are the key sites of heme biosythesis? |
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Definition
| Erythroid (85% of total) and Liver (for Cytochrome P450). |
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Term
| How is heme synthesis regulated in the liver? |
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Definition
| Mostly through ALA sythase activity. Regulation can be done through feedback by heme (down-regulation) or through induction of toxins (up-regulation). |
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Term
| How often do erythroid cells produce heme? |
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Definition
| RBC's sythesize heme once in their lifetimes and in vast quantities. |
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Term
| Name the two types of erythropoetic porphorias and the actions of each. |
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Definition
| 1) CEP: Congenital Erythropoetic Porphyria. Uro'gen III Cosynthase deficiency. Buildup of Uro'gen I and Copro'gen I. Photosensitivity, werewolf. 2) EPP: Erythroid Protophoria. Ferrochetelase defiency. Similar symp's to CEP but milder. |
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Term
| Name the two types of liver porphyrias and the actions of each. |
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Definition
| 1) AIP: Acute intermittent porphyria. PBG deficiency. Need exogenous chemicals to bring on symptoms (King George). Buildup of ALA and PBG (ALA looks like GABA). 2) PCT: Porphyria cutanea tarda. Deficiency in Uro'gen decarboxylase. No symptoms until liver damage (alcohol, birth control). Depletion of iron stores bring alleviation of symptoms. |
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Term
| What organs play a role in heme breakdown? |
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Definition
| Spleen. Liver and bone marrow play secondary roles. |
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Term
| True or false: Hemepexin binds methemoglobin dimers to prevent loss of iron via the kidney. |
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Definition
| False. Haptoglobin does that. Hemepexin binds free heme. |
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Term
| Outline the products of the heme catabolism pathway. |
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Definition
| Hemoglobin (in spleen) à Globin (to AA's) + Heme à Iron (recycled by ferritin, hemosiderin, transferrin) + BV à BR à BR-Alb (in blood) à BR (in liver) à conj-BR à Bile à Urobilinogens à (liver-recycled) + Urine (kidney) + Urobilins (color of feces and urine) |
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Term
| What would a buildup of direct-reacting bilirubin indicate? |
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Definition
| Direct reacting means water soluble which means conjugated bilirubin. This indicates post-hepatic jaundice-a blockage of bile flow from the liver. |
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Term
| What would a buildup of unconjugated bilirubin indicate? |
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Definition
| Pre-hepatic jaundice. Unconjugated bilirubin is indirect-reacting and not soluble in water. If in the blood, it indicates that heme is being broken down at a faster rate than the liver can process it (hemolytic anemia). If the unconjugated bilirubin is in the liver, it is an indication of hepatic jaundice. |
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Term
| What are hemosiderrin and ferritin? |
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Definition
| Hemosiderrin is a degraded form of ferritin. Both store iron. |
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Term
| What's the deal with transferrin? |
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Definition
| Transferrin is a receptor molecule that mediates the transport of heme into cells (Apo=no Fe; Ferro=Fe-bound). It is synthesized in the liver, localized in the plasma, and recycled after use. Transferrin binds Fe3+ (ferric) at pH7, takes it into the cell through receptor-mediated endocytosis (clathrin vesiculation), and releases Fe3+ at pH5. |
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