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Porphyrins and Hemo

SCC chemistry 11-28-11

QuestionAnswer
1. What are porphyrins? Porphyrins are chemical intermediates in the synthesis of hemoglobin, myoglobin and other respiratory pigments called cytochromes.
2. What is the clinical significance of the porphyrins? They are analyzed in the laboratory to aid in the diagnosis of a group of disorders call the "porphyrias", which result from disturbances in heme synthesis. (Remember - heme is a structural part of the hemoglobin molecule.)
3. What do elevated levels of porphyrins indicate? The presence of excess amounts of porphyrins in urine, feces or blood indicates a metabolic block in heme synthesis.
4. What types of specimens can be collected to measure porphyrin levels? Urine, feces, or blood
5. What three porphyrin compounds are of clinical significance to humans and in what type of specimen can they be measured? "Elevated" levels of any of these compounds in body fluids are an indication of abnormal heme synthesis. URO... is excreted in urine. PROTO... is excreted in feces. COPRO... i excreted in either urine or feces.
6. What are the two main sources of porphyrin synthesis? Bone Marrow & Liver
7. What is a porphyria, and what are the clinical significance of these disorders? The porphyrias are inherited or acquired enzyme deficiencies that result in overproduction of heme precursors in the bone marrow (erythropoietic porphyrias) or the liver (hepatic porphyrias).
8. What is a secondary porphyria or porphyrinuria? How is this disorder acquired? Acquired conditions that are due to another disorder, toxin or drug interference defects in heme synthesis, in which mild to moderate increase in excretion of urinary porphyrins are seen
9. What is the role of hemoglobin (hgb) in the body? Hemoglobin's major role is transportation of oxygen to the tissues and transportation of CO2 back to the lungs.
10. Explain the structure of hemoglobin. composed of two parts: heme and globin proteins. The heme portion contains the porphyrin "ring" with iron chelated (attached) in the center.
Where is the site of "reversible" oxygen attachment? The iron that is chelated (attached0 to the center of the heme portion.
The globin portion contains the globin chains what are they made of? Alpha, beta, gamma or delta chaains in any combos.
globin chains are composed of amino acids linked togeterh to form what? Protein
Globin chains are ________chains? Protein
The complete hemoglobin molecule consists of how many heme groups? attached to what? May carry up to how many molecules of oxygen? four heme groups attached to each of four globin chains and may carry up to four molecules of oxygen. (Each molecule of oxygen may be attached to an iron molecule).
What are the types of globin chains and their %'s? Hemoglobin A1 (96-97%, 2 alpha 2 beta chains Hemoglobin A2 (3%)2 alpha 2 delta Hemoglobin F (1%) 2 alpha 2 gamma
12. What are hemoglobinopathies? Defects in hemoglobin structure
13. What are thalassemias? Defects in rate and quantity of hemoglobin production
14. List the possible four types of abnormal globin chain production that result in thalassemias. 1. amino acid substitutions 2. amino acid deletion 3. elongated globin chains resulting from chain termination, frame shift, or other mutations 4. fused or hybrid globin chains resulting from chromosomal crossovers
15. What are the two major categories of thalassemias? What is the abnormality seen in each? In alpha thalassemia, the alpha-globin chain is absent or reduced. In beta thalassemia, the beta-globin chain is absent or reduced.
16. Where does production of hemoglobin take place? Synthesis of hemoglobin occurs in the immature RBCs in the bone marrow.
17. What three factors does normal hemoglobin production depend on? Normal synthesis depends on adequate iron supply as well as normal synthesis of heme and globin molecules.
18. Where is heme synthesized? Heme is synthesized in the mitochrondria of the cells.
19. Where are globin chains synthesized? Globin synthesis takes place in cytoplasmic ribosomes in the cells.
20. What is transferrin? It is a plasma protein that transports iron to the developing RBC.
21. What are the two pathways for hemoglobin degradation (breakdown)? Normal is Extravascular (outside of the circulatory system in momonuclear phagocyte sys. The alternate is intravascular degradation (<10% happens this way)
22. What is haptoglobin and what is its clinical significance? It is a plasma protein that prevents the loss of plasma hemoglobin through renal excretion.
23. What is meant by a "qualitative" defect (or abnormality)? (think question...) A structural abnormality
24. What is meant by a "quantitative" defect (or abnormality)? (think question...) Defect in rate of synthesis (decreased or absent synthesis production)
26. What is Hgb S? Hgb C? Hgb SC? They are the most common hemoglobinopathies.
27. Why are thalassemias considered quantitative abnormalities? The thalassemias are a group of disorders in which defects in the rate of globin chain synthesis occurs. The globin chains are normal in structure.
28. What do the RBCs look like in thalassemic conditions (generally speaking...)? Microcytic, hypochromic
29. What is a thalassemia minor? A heterozygous thalassemia that mimics an iron deficiency anemia. In thalassemia minors, only one type of globin chain synthesis is affected.
What is thalassemia major? A homozygous thalassemia which is more severe than minor, it's either lethal at birth or in childhood because both types of globin chain synthesis are affected.
30. What is myoglobin, and what is its clinical significance? Myoglobin is a heme protein found only in skeletal and cardiac muscle in humans. Measurement of myoglobin levels assists in the diagnosis of myocardial infarction (MI) or muscular dystrophy
Created by: nizhoni
 

 



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