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Questions and Answers
Which of the following is NOT a function of amino acids?
Which of the following is NOT a function of amino acids?
- Formation of porphyrins (correct)
- Precursors of nitrogen-containing compounds
- Building blocks for proteins
- Formation of neurotransmitters
What metal ions do porphyrins readily bind to?
What metal ions do porphyrins readily bind to?
- Fe3+
- Mg2+
- Fe2+ (correct)
- Cu2+
Where do porphyrins occur in the body?
Where do porphyrins occur in the body?
- In hemoglobin
- In cataleases
- In cytochromes
- All of the above (correct)
What is the most prevalent metalloporphyrin in humans?
What is the most prevalent metalloporphyrin in humans?
Where is heme produced in the body?
Where is heme produced in the body?
What proteins contain heme?
What proteins contain heme?
Where is heme synthesized in the body?
Where is heme synthesized in the body?
What factor influences heme synthesis in the liver?
What factor influences heme synthesis in the liver?
Which molecule is derived from two molecules of -aminolevulinate?
Which molecule is derived from two molecules of -aminolevulinate?
How many molecules of porphobilinogen come together to form protoporphyrin?
How many molecules of porphobilinogen come together to form protoporphyrin?
What is the step catalyzed by ferrochelatase in heme biosynthesis?
What is the step catalyzed by ferrochelatase in heme biosynthesis?
What are derangements of porphyrin metabolism known clinically as?
What are derangements of porphyrin metabolism known clinically as?
Which enzyme controls the rate limiting step of porphyrin synthesis?
Which enzyme controls the rate limiting step of porphyrin synthesis?
What is the absolute requirement for the production of aminolevulinate (ALA)?
What is the absolute requirement for the production of aminolevulinate (ALA)?
Which enzyme is extremely sensitive to inhibition by heavy metal ions?
Which enzyme is extremely sensitive to inhibition by heavy metal ions?
Which form of the enzyme is mutated in sideroblastic anemia?
Which form of the enzyme is mutated in sideroblastic anemia?
Which drugs increase hepatic ALA synthase activity?
Which drugs increase hepatic ALA synthase activity?
What is the result of lead poisoning on ALA dehydrase activity?
What is the result of lead poisoning on ALA dehydrase activity?
Where does the dehydration of ALA to form porphobilinogen occur?
Where does the dehydration of ALA to form porphobilinogen occur?
Which enzyme is responsible for the condensation of 4 molecules of porphobilinogen to form Preuroporphyrinogen?
Which enzyme is responsible for the condensation of 4 molecules of porphobilinogen to form Preuroporphyrinogen?
Which enzyme is responsible for the formation of Uroporphyrinogen ІІІ?
Which enzyme is responsible for the formation of Uroporphyrinogen ІІІ?
Which enzyme is responsible for the formation of Coproporphyrinogen?
Which enzyme is responsible for the formation of Coproporphyrinogen?
Where does Coproporphyrinogen move after its formation?
Where does Coproporphyrinogen move after its formation?
Which enzyme is responsible for the formation of Protoporphyrinogen?
Which enzyme is responsible for the formation of Protoporphyrinogen?
Which enzyme is responsible for the formation of Protoporphyrin?
Which enzyme is responsible for the formation of Protoporphyrin?
How is Fe2+ introduced into protoporphyrin IX during the formation of Heme?
How is Fe2+ introduced into protoporphyrin IX during the formation of Heme?
Which enzyme is enhanced by the rate of Fe2+ introduction into protoporphyrin IX during heme formation?
Which enzyme is enhanced by the rate of Fe2+ introduction into protoporphyrin IX during heme formation?
Which enzyme is inactivated by lead in lead poisoning?
Which enzyme is inactivated by lead in lead poisoning?
What is the result of lead poisoning on heme production?
What is the result of lead poisoning on heme production?
What is the main cause of anemia in lead poisoning?
What is the main cause of anemia in lead poisoning?
What is the collective term for a group of human diseases caused by genetic defects in the biosynthesis of porphyrins?
What is the collective term for a group of human diseases caused by genetic defects in the biosynthesis of porphyrins?
What is the characteristic color of the urine in patients with porphyria?
What is the characteristic color of the urine in patients with porphyria?
What can cause a buildup of ALA and porphobilinogen, leading to attacks of acute abdominal pain and neurological dysfunction?
What can cause a buildup of ALA and porphobilinogen, leading to attacks of acute abdominal pain and neurological dysfunction?
What is the main treatment for controlling the symptoms of most porphyrias?
What is the main treatment for controlling the symptoms of most porphyrias?
Which type of porphyria primarily affects the bone marrow?
Which type of porphyria primarily affects the bone marrow?
Which type of porphyria is characterized by both abdominal and neuropsychiatric signs?
Which type of porphyria is characterized by both abdominal and neuropsychiatric signs?
Which individuals with an enzyme defect prior to the synthesis of tetrapyrroles manifest abdominal and neuropsychiatric signs?
Which individuals with an enzyme defect prior to the synthesis of tetrapyrroles manifest abdominal and neuropsychiatric signs?
Which porphyria is characterized by acute attacks of gastrointestinal and neurologic/psychiatric manifestations, often precipitated by the administration of certain drugs?
Which porphyria is characterized by acute attacks of gastrointestinal and neurologic/psychiatric manifestations, often precipitated by the administration of certain drugs?
Which enzyme deficiency is responsible for the development of porphyria cutanea tarda?
Which enzyme deficiency is responsible for the development of porphyria cutanea tarda?
Which porphyria is the most common form and is typically characterized by skin blisters, itching, and skin darkening?
Which porphyria is the most common form and is typically characterized by skin blisters, itching, and skin darkening?
Which enzyme deficiency is responsible for the development of erythropoietic protoporphyria?
Which enzyme deficiency is responsible for the development of erythropoietic protoporphyria?
Which porphyria is typically not expressed unless patients either take drugs that cause an increase in porphyrin synthesis or drink large amounts of alcohol?
Which porphyria is typically not expressed unless patients either take drugs that cause an increase in porphyrin synthesis or drink large amounts of alcohol?
What triggers the expression of porphyria cutanea tarda in some patients?
What triggers the expression of porphyria cutanea tarda in some patients?
What is the color of urine in porphyria cutanea tarda when exposed to natural light?
What is the color of urine in porphyria cutanea tarda when exposed to natural light?
What is the color of urine in porphyria cutanea tarda when exposed to fluorescent light?
What is the color of urine in porphyria cutanea tarda when exposed to fluorescent light?
What treatment is recommended during acute porphyria attacks?
What treatment is recommended during acute porphyria attacks?
What is the most effective way to prevent symptoms in patients with porphyria cutanea tarda?
What is the most effective way to prevent symptoms in patients with porphyria cutanea tarda?
Which condition can cause elevated unconjugated bilirubin levels in the blood, leading to jaundice?
Which condition can cause elevated unconjugated bilirubin levels in the blood, leading to jaundice?
What can obstruct the bile duct and prevent the passage of bilirubin into the intestine, causing jaundice?
What can obstruct the bile duct and prevent the passage of bilirubin into the intestine, causing jaundice?
Which of the following is a sign of obstructive jaundice?
Which of the following is a sign of obstructive jaundice?
What are the two main types of jaundice?
What are the two main types of jaundice?
What causes hemolytic jaundice?
What causes hemolytic jaundice?
What causes obstructive jaundice?
What causes obstructive jaundice?
Explain why newborn infants, particularly premature babies, often accumulate bilirubin.
Explain why newborn infants, particularly premature babies, often accumulate bilirubin.
What can happen if newborns have significantly elevated bilirubin levels?
What can happen if newborns have significantly elevated bilirubin levels?
How are newborns with significantly elevated bilirubin levels treated?
How are newborns with significantly elevated bilirubin levels treated?
Why is the conversion of bilirubin to more polar and water-soluble isomers important?
Why is the conversion of bilirubin to more polar and water-soluble isomers important?
Which enzyme is responsible for the conversion of bilirubin to more polar and water-soluble isomers?
Which enzyme is responsible for the conversion of bilirubin to more polar and water-soluble isomers?
What can cause toxic encephalopathy (kernicterus) in newborns with significantly elevated bilirubin levels?
What can cause toxic encephalopathy (kernicterus) in newborns with significantly elevated bilirubin levels?
What is the purpose of treating newborns with significantly elevated bilirubin levels with blue fluorescent light?
What is the purpose of treating newborns with significantly elevated bilirubin levels with blue fluorescent light?
Why do newborn infants, particularly premature babies, often accumulate bilirubin?
Why do newborn infants, particularly premature babies, often accumulate bilirubin?
Which enzyme is responsible for the conversion of heme to biliverdin?
Which enzyme is responsible for the conversion of heme to biliverdin?
What is the color of bilirubin?
What is the color of bilirubin?
Where does the conversion of biliverdin to bilirubin occur?
Where does the conversion of biliverdin to bilirubin occur?
What is the main route of excretion for bilirubin?
What is the main route of excretion for bilirubin?
What is the main source of heme for degradation?
What is the main source of heme for degradation?
What happens to Fe2+ during the conversion of heme to biliverdin?
What happens to Fe2+ during the conversion of heme to biliverdin?
What is the final product of heme catabolism?
What is the final product of heme catabolism?
What is the main route of excretion for bilirubin diglucuronide?
What is the main route of excretion for bilirubin diglucuronide?
What is the main function of ferritin during heme catabolism?
What is the main function of ferritin during heme catabolism?
What is the color of urine in porphyria cutanea tarda when exposed to natural light?
What is the color of urine in porphyria cutanea tarda when exposed to natural light?
Which enzyme is responsible for the conversion of urobilinogen to stercobilin in the intestine?
Which enzyme is responsible for the conversion of urobilinogen to stercobilin in the intestine?
What compound gives urine its yellow color?
What compound gives urine its yellow color?
What causes the yellow to yellow-green color seen in patients with jaundice?
What causes the yellow to yellow-green color seen in patients with jaundice?
What is the normal production of bilirubin per day?
What is the normal production of bilirubin per day?
What type of jaundice is caused by massive lysis of red blood cells?
What type of jaundice is caused by massive lysis of red blood cells?
What causes obstructive jaundice?
What causes obstructive jaundice?
What is the treatment for newborns with significantly elevated bilirubin levels?
What is the treatment for newborns with significantly elevated bilirubin levels?
What enzyme deficiency is responsible for the development of porphyria cutanea tarda?
What enzyme deficiency is responsible for the development of porphyria cutanea tarda?
What is the precursor for the synthesis of nitric oxide (NO)?
What is the precursor for the synthesis of nitric oxide (NO)?
What is the main function of glutathione (GSH)?
What is the main function of glutathione (GSH)?
What is the first step in heme catabolism?
What is the first step in heme catabolism?
What is the enzyme responsible for the conversion of heme to biliverdin?
What is the enzyme responsible for the conversion of heme to biliverdin?
What is the color of biliverdin?
What is the color of biliverdin?
What happens to Fe2+ during the conversion of heme to biliverdin?
What happens to Fe2+ during the conversion of heme to biliverdin?
What is the second step in heme catabolism?
What is the second step in heme catabolism?
What is the enzyme responsible for the conversion of biliverdin to bilirubin?
What is the enzyme responsible for the conversion of biliverdin to bilirubin?
What is the color of bilirubin?
What is the color of bilirubin?
Where is bilirubin largely insoluble?
Where is bilirubin largely insoluble?
How does bilirubin travel in the bloodstream?
How does bilirubin travel in the bloodstream?
What is bilirubin transformed into in the liver?
What is bilirubin transformed into in the liver?
What is the role of stercobilin in the intestine?
What is the role of stercobilin in the intestine?
What is the compound that gives urine its yellow color?
What is the compound that gives urine its yellow color?
What causes the yellow to yellow-green color seen in patients with jaundice?
What causes the yellow to yellow-green color seen in patients with jaundice?
What is the excess capacity of the liver to conjugate and excrete bilirubin per day?
What is the excess capacity of the liver to conjugate and excrete bilirubin per day?
What can cause unconjugated bilirubin levels to increase in the blood?
What can cause unconjugated bilirubin levels to increase in the blood?
What is the treatment for newborns with significantly elevated bilirubin levels?
What is the treatment for newborns with significantly elevated bilirubin levels?
What is the precursor for the synthesis of nitric oxide?
What is the precursor for the synthesis of nitric oxide?
What is the important energy buffer in skeletal muscle?
What is the important energy buffer in skeletal muscle?
What is the precursor for the synthesis of glutathione?
What is the precursor for the synthesis of glutathione?
What is the function of glutathione?
What is the function of glutathione?
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Study Notes
Heme Catabolism
- Heme catabolism involves the degradation of hemoglobin from red blood cells, which produces bilirubin.
- 85% of heme destined for degradation comes from red blood cells, and 15% is from cytochromes from extra erythroid tissues.
Step 1: Conversion of Heme to Biliverdin
- Catalyzed by heme oxygenase (HO)
- Converts heme to biliverdin, a linear (open) tetrapyrrole derivative
- Produces free Fe2+ and CO
- Biliverdin has a pale-green coloration
Step 2: Biliverdin to Bilirubin
- Biliverdin is converted to bilirubin
- Catalyzed by biliverdin reductase
- Biliverdin is reduced, forming the yellow-brown bilirubin
Step 3: Bilirubin to Bile Pigments
- Bilirubin is largely insoluble in plasma and travels in the bloodstream as a complex with serum albumin
- Liver: Bilirubin is transformed to the bile pigment bilirubin diglucuronide (more soluble) which is secreted with other components of bile into the small intestine
- Intestine: Bilirubin diglucuronide is converted to urobilinogen by microbial enzymes
- Kidney: Some urobilinogen is reabsorbed into the blood and transported to the kidney, where it is converted to urobilin, the compound that gives urine its yellow color
Jaundice
- Hemolytic jaundice: Massive lysis of red blood cells in conditions like sickle cell anemia, G6PD deficiency, or malaria
- Obstructive jaundice: Obstruction of the bile duct (by tumor, gallstones, etc.) preventing passage of bilirubin into the intestine
- Jaundice in newborns: Newborn infants, particularly premature babies, often accumulate bilirubin, because the activity of hepatic bilirubin glucuronyl transferase is low at birth
- Hepatocellular jaundice: Damage to liver cells (for example, in patients with cirrhosis or hepatitis) can cause unconjugated bilirubin levels to increase in the blood as a result of decreased conjugation
Other Amino Acid Products
- GABA: Glutamate decarboxylation gives rise to -aminobutyrate (GABA), an inhibitory neurotransmitter
- Nitric Oxide: Arginine is a precursor for its synthesis, and it plays a role in a range of physiological processes, including control of blood pressure and neurotransmission
- Creatine: Synthesized from glycine and arginine; and methionine, in the form of S-adenosylmethionine, acts as methyl group donor
- Glutathione (GSH): Derived from cysteine, glutamate, and glycine, and serves as a redox buffer and detoxifying agent
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