38 Questions
What is a porphin?
A cyclic compound formed by the linkage of 4 pyrrole rings
What is the function of the heme group in hemoglobin and myoglobin?
To reversibly bind oxygen
What is the result of a deficiency of one of the enzymes needed for heme synthesis?
Increased production and excretion of porphyrins and/or their precursors
What type of porphyria is caused by lead poisoning?
Any type of porphyria
What is the function of the heme group in catalase?
To catalyze the breakdown of hydrogen peroxide
What is the result of anemia in patients with porphyria?
Decreased production of heme
What is the result of photosensitivity in patients with porphyria?
Formation of damage oxygen radicles
What is the inheritance pattern of congenital erythropoietic porphyria?
Autosomal recessive
What is the primary function of myoglobin in muscle cells?
To act as a reservoir and carrier for oxygen
What is the structure of the myoglobin molecule?
A compact molecule with 80% α-helix structure
How many oxygen molecules can myoglobin bind?
One
What is the partial pressure of oxygen needed to achieve half-saturation of the binding sites on myoglobin?
1 mm Hg
What happens to the oxygen dissociation curve when the pH is raised or the concentration of CO2 in the lungs is lowered?
It shifts to the left
What is the Bohr effect?
The decrease in oxygen binding capacity of hemoglobin at low pH
What happens to the oxygen dissociation curve in the Bohr effect?
It shifts to the right
What is the effect of 2,3-bisphosphoglycerate (2,3 BPG) on the oxygen affinity of hemoglobin?
It decreases the oxygen affinity
What is the purpose of 2,3-BPG in the RBCs?
To release oxygen efficiently in the tissues
What is the primary difference in oxygen binding between myoglobin and hemoglobin?
Myoglobin has a higher oxygen affinity than hemoglobin
What happens to the oxygen affinity of hemoglobin in the absence of 2,3-BPG?
It increases
What is the function of the heme group in myoglobin?
To bind oxygen
What is the function of Hb A2?
It is synthesized in the adult at low levels compared to Hb A
What can happen to Hb A?
It can become modified by the covalent addition of a hexose
What occurs due to an imbalance in the synthesis of globin chains in thalassemias?
A defect in either α or β-globin chain synthesis
What leads to the formation of α2β2 (Hb A) in normal conditions?
Coordination in the synthesis of α and β-globin chains
Which enzyme catalyzes the first step in the degradation of heme?
Heme oxygenase
What pigment is produced as a result of the first step in the degradation of heme?
Biliverdin
How is bilirubin transported to the liver?
Bound to albumin
What increases the solubility of bilirubin in the hepatocyte?
Addition of glucuronic acid
What is formed when bilirubin diglucuronide is hydrolyzed and reduced by bacteria in the gut?
Urobilinogen
What is the primary location where red blood cells are degraded after approximately 120 days in circulation?
Reticuloendothelial system
What pigment gives feces its characteristic brown color?
Stercobilin
What is the main cause of hemolytic jaundice?
Massive lysis of red blood cells
What is the fate of reabsorbed urobilinogen in the portal blood?
Participates in the enterohepatic urobilinogen cycle
Which type of jaundice involves an obstruction of the bile duct?
Obstructive jaundice
What causes the urine to turn dark in hepatocellular jaundice?
Increase in urobilinogen
Why do newborns often develop jaundice?
Immature liver function
What enzyme's activity is low at birth, contributing to jaundice in newborns?
Hepatic bilirubin glucuronyltransferase
What is the end product of heme catabolism?
Bilirubin
This quiz covers the structure and metabolism of porphyrins, including their composition, bonding, and role in hemoglobin. It's a perfect resource for biochemistry students.
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