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C14
Schmitt - lecture notes (heme)
18
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Not Applicable
10/21/2007

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Term
Structure of heme a?
Definition
M, *, M. V, M, P, P, M
Term
Structure of heme b?
Definition
M, V, M, V, M, P, P, M
Term
Structure of heme c?
Definition
M, cys, M, cys, M, P, P, M
Term
Name some enzymes and proteins for which heme is a prosthetic group. (The list is long.)
Definition
Hemoglobin, Myoglobin, Cytrochrome C & P450, Catalase, Ub-cytochrome C Reductase, Cytochrome C Oxidase, Tryptophan pyrolase, Neutrophil NADPH Oxidase, NO Synthase, Cystathionase.
Term
Outline the heme synthesis pathway products. Think about location of products.
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.
Term
Outline the heme synthesis pathway enzymes. Think about location of products.
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
Term
What are the key sites of heme biosythesis?
Definition
Erythroid (85% of total) and Liver (for Cytochrome P450).
Term
How is heme synthesis regulated in the liver?
Definition
Mostly through ALA sythase activity. Regulation can be done through feedback by heme (down-regulation) or through induction of toxins (up-regulation).
Term
How often do erythroid cells produce heme?
Definition
RBC's sythesize heme once in their lifetimes and in vast quantities.
Term
Name the two types of erythropoetic porphorias and the actions of each.
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.
Term
Name the two types of liver porphyrias and the actions of each.
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.
Term
What organs play a role in heme breakdown?
Definition
Spleen. Liver and bone marrow play secondary roles.
Term
True or false: Hemepexin binds methemoglobin dimers to prevent loss of iron via the kidney.
Definition
False. Haptoglobin does that. Hemepexin binds free heme.
Term
Outline the products of the heme catabolism pathway.
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)
Term
What would a buildup of direct-reacting bilirubin indicate?
Definition
Direct reacting means water soluble which means conjugated bilirubin. This indicates post-hepatic jaundice-a blockage of bile flow from the liver.
Term
What would a buildup of unconjugated bilirubin indicate?
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.
Term
What are hemosiderrin and ferritin?
Definition
Hemosiderrin is a degraded form of ferritin. Both store iron.
Term
What's the deal with transferrin?
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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