37 Questions
What is the significance of positive cooperativity in hemoglobin?
It increases the affinity for O2 in adjacent subunits
Which of the following is NOT a positive effector that increases oxygen binding to hemoglobin?
High concentration of 2,3-bisphosphoglycerate (BPG)
Where does heme synthesis mainly occur?
Mitochondria and cytosol
What is the negative effect of negative effectors on hemoglobin?
Decrease binding of oxygen and facilitate its delivery to tissue
What is the role of heme in hemoglobin?
Participates in the structure of hemoglobin
Which of the following is true about 2,3-bisphosphoglycerate (BPG)?
It's a positive effector that decreases oxygen binding to hemoglobin
What is the location of heme synthesis for hemoglobin production?
Red blood cell progenitor cells
Which enzyme deficiency is associated with Acute Intermittent Porphyria?
Porphobilinogen deaminase
What are the typical symptoms of Porphyria cutanea tarda?
Photosensitivity and dark red/brown colored urine
Which pathway intermediate accumulation causes neurological symptoms in Porphyrias?
Aminolevulinic acid
Which type of Porphyria does NOT exhibit photosensitivity?
Acute intermittent porphyria
What is the key pathway intermediate that leads to the characteristic symptoms of Porphyrias?
Aminolevulinic acid
Which enzyme deficiency characterizes Porphyria cutanea tarda?
Uroporphyrinogen decarboxylase
Which of the following drugs can worsen the symptoms of Porphyrias by stimulating the heme synthesis pathway?
Barbiturates
Where does the degradation of abnormal red blood cells primarily occur?
Spleen
Which enzyme is the rate-limiting enzyme in heme synthesis?
ALA synthase
What inhibits ALA synthase in the liver when there is an excess of heme?
Hemin
Lead poisoning primarily affects which enzymes in heme synthesis?
ALA synthase & Ferrochelatase
Which deficiency leads to the inhibition of ALA synthase?
Vitamin B6 deficiency
What role does vitamin B6 play in heme synthesis?
Cofactor for ALA synthase
How does lead poisoning differentiate itself from porphyrias?
By inducing ALA dehydratase deficiency without a PBG increase
Which enzyme introduces Fe2+ into the heme ring in the final step of heme synthesis?
Ferrochelatase
What is the final product of heme degradation in macrophages?
Biliverdin
How is iron released from hemoglobin in macrophages stored?
Bound to ferritin
What enzyme reduces biliverdin to bilirubin in the cytosol?
Biliverdin reductase
In what form is bilirubin transported in the blood?
Bound to serum albumin
Which of the following can be excreted in urine?
Urobilinogen
What is the fate of most urobilinogen produced in the gastrointestinal tract?
Excreted in feces as stercobilin
What can occur if there is an accumulation of unconjugated bilirubin in the basal ganglia of the brain?
Death or mental retardation
How is bilirubin converted to urobilinogen in the gastrointestinal tract?
Reduction by intestinal bacteria
What is the correct composition of globin chains in a hemoglobin molecule?
2 α and 2 β subunits
How many pyrolle rings are present in the heme structure?
4
In what state does hemoglobin have a higher affinity for O2?
R state
How many oxygen molecules can each Hb molecule bind to?
4
Which amino acid binds to the 5th coordination bond of iron in the heme group?
Histidine
In which state does deoxygenated hemoglobin exist?
T state
What is the oxidation state of iron in the heme moieties?
Ferrous (Fe2+)
Explore the regulation of heme synthesis, focusing on the rate-limiting enzyme ALA synthase. Learn about the inhibitory effects of heme on ALA synthase and the role of vitamin B6 as a coenzyme in the process.
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