Porphyrins and Porphyrias

Question 1

1. The precursors of the tetrapyrrole ring structure of
   porphyrin are:
   a. 5-aminolevulinic acid and iron.
   b. acetyl CoA and porphyrin.
   c. succinyl CoA and glycine.
   d. zinc and porphyrinogen.

Answer 1

c. succinyl CoA and glycine.

Question 2

2. The important initial screening test that allows for differentiation between the two categories of porphyria is:

a. serum coproporphyrin.
b. urine aminolevulinic acid (ALA) and porphobilinogen
(PBG).
c. serum zinc protophyrin.
d. red blood cell zinc protoporphyrin.

Answer 2

b. urine aminolevulinic acid (ALA) and porphobilinogen
(PBG).

Question 3

3. Another name for protoporphyrin that contains iron is:

a. heme.
b. PBG.
c. coproporphyrin.
d. ferrochelatase.

Answer 3

a. heme.

Question 4

4. The skin lesions and photosensitivity observed in patients
   with nonacute cutaneous porphyrias are the result of:

a. autonomic neuropathy.
b. excessive production of ALA.
c. accumulation of porphyrins in the liver.
d. excess presence of porphyrins in skin that generate
oxygen radicals

Answer 4

d. excess presence of porphyrins in skin that generate oxygen radicals

Question 5

5. In lead toxicity, what replaces iron as a substrate for
   ferrochelatase to be incorporated into protoporphyrin?

a. Carbon dioxide
b. Zinc
c. Copper
d. Lead

Answer 5

b. Zinc

Question 6

6. The most common of all the porphyria disorders is:

a. variegate porphyria.
b. acute intermittent porphyria.
c. porphyria cutanea tarda.
d. congenital erythropoietic porphyria

Answer 6

c. porphyria cutanea tarda.

Question 7

7. The initial steps of heme synthesis occur in the:

a. mitochondrion.
b. cytosol.
c. endoplasmic reticulum.
d. cell nucleus

Answer 7

a. mitochondrion.

Question 8

8. The best specimen type for analyzing porphobilinogen is:

a. heparinized plasma separated and frozen immediately after collection.
b. a 24-hour urine collection collected in a dark brown
container and preserved with 0.1% HCl.
c. a fresh early morning urine specimen collected without preservative and protected from light.
d. blood anticoagulated with EDTA and protected from
light

Answer 8

c. a fresh early morning urine specimen collected without preservative and protected from light.

Question 9

9. Erythropoietic protoporphyria is characterized by which
   of the following symptoms?

a. Flaccid quadriparesis caused by the accumulation of
porphobilinogen in muscle
b. Lifelong acute photosensitivity caused by protoporphyrin-IX accumulation in skin
c. Liver damage and hepatic siderosis caused by iron
accumulation in cells
d. Severe abdominal pain and peripheral neuropathy caused by the induction of hepatic cytochromes

Answer 9

b. Lifelong acute photosensitivity caused by protoporphyrin-IX accumulation in skin

Question 10

10. The reduced form of a porphyrin is known as a:

a. protoporphyrin.
b. heme molecule.
c. pyrrole ring.
d. porphyrinogen.

Answer 10

d. porphyrinogen