Question 1

Which of the following characteristics is true of hemosiderin that differentiates it from ferritin?&#10;A)Hemosiderin may contain up to approximately 4500 iron atoms.&#10;B)Hemosiderin is a readily mobilized storage form of iron.&#10;C)Hemosiderin is derived from ferritin that has lost some of its surface protein, causing insolubility.&#10;D)Hemosiderin is too small to be observed by light microscopy, whereas ferritin can be observed in tissue stained with Prussian blue dye.

Accepted Answer

Hemosiderin is an insoluble complex derived from ferritin that has lost part of its surface protein.The function of the surface protein is to maintain complex solubility.Even though hemosiderin has a higher iron concentration than ferritin, the insolubility of hemosiderin causes a delay in release of iron from the complex.

Question 2

Porphyrias are characterized by reduced activity or a deficiency of a specific enzyme.If methods were available to accurately measure activity of each enzyme in the heme synthetic pathway, why would the red blood cell not be a good place to quantify enzyme activity?

A)Red blood cells do not carry out heme synthesis.
B)Approximately half of heme synthesis in the red blood cell occurs within the mitochondrion, which is lost as these cells mature.
C)Enzyme assays cannot be performed on enzymes that are isolated with red blood cells.
D)Red blood cells must be hemolyzed to allow enzyme measurement, which would produce a spectral interference.

Accepted Answer

The synthetic pathway for heme synthesis begins and ends in the mitochondrion of the cell.The middle steps in this pathway occur in the cytoplasm.Given that developing red blood cells lose their mitochondria as they mature, only half of the enzymes of the heme synthetic pathway would be available for analysis in circulating red blood cells.

Question 3

In variegate hepatic porphyria, which of the following would show the greatest increase?&#10;A)urinary uroporphyrin&#10;B)urinary coproporphyrin&#10;C)fecal protoporphyrinogen&#10;D)decal protoporphyrin

Accepted Answer

Variegate porphyria is associated with a partial deficiency of protoporphyrinogen oxidase, which is responsible for converting protoporphyrinogen to protoporphyrin in the heme synthetic pathway.Thus there is a buildup of protoporphyrinogen.Protoporphyrinogen, as with all porphyrinogens, is spontaneously and irreversibly oxidized to its corresponding porphyrin, protoporphyrin.Protoporphyrin, now outside of the mitochondrion, is unable to participate in heme synthesis and is excreted at increased levels in the feces.

Question 4

______ is the porphyrin most likely to be exclusively excreted in urine, and ______ is the porphyrin most likely to be exclusively excreted in feces.______ has the greatest chance of appearing in either urine or feces.

A)Protoporphyrin, coproporphyrin, uroporphyrin
B)Uroporphyrin, protoporphyrin, coproporphyrin
C)Coproporphyrin, uroporphyrin, protoporphyrin
D)Protoporphyrin, uroporphyrin, coproporphyrin

Accepted Answer

Uroporphyrin contains eight carboxyl groups, coproporphyrin contains four carboxyl groups, and protoporphyrin contains two carboxyl groups.Uroporphyrin is the most polar of the three porphyrins, making it the most water soluble and the most likely to appear in urine.Protoporphyrin is the least polar of the three porphyrins and will likely be excreted only in feces.Coproporphyrin is intermediary in its polarity, allowing this porphyrin to appear in both urine and feces.

Question 5

Which of the following is/are true of hepcidin?&#10;A)It controls the flow of iron out of the intestinal cells by inhibiting iron release.&#10;B)High levels promote release of iron into the circulation.&#10;C)Low levels restrict the release of iron from intestinal cells into the circulation.&#10;D)all of the above

Accepted Answer

Hepcidin is a protein hormone produced by the liver; it is important in the regulation of iron balance.High levels of hepcidin restrict the flow of iron out of intestinal cells by binding to ferroportin and inhibiting iron release.Low levels of hepcidin do not interfere with the flow of iron from the intestine to the circulation.

Question 6

At present, the one heme enzyme that is routinely measured in clinical laboratories is:&#10;A)porphobilinogen deaminase&#10;B)uroporphyrinogen III synthase&#10;C)coproporphyrinogen oxidase&#10;D)ferrochelatase

Accepted Answer

Measurements of the heme enzymes have shown limited application in the clinical laboratory because of problems such as technical difficulties with assays and the fact that not all heme enzymes may be available in the mature red blood cell.One enzyme that is measured regularly in clinical laboratories is porphobilinogen deaminase.Porphobilinogen deaminase activity is decreased in patients with acute intermittent porphyria.

Question 7

In which of the following neurological porphyrins is a parallel increase in &#948;-aminolevulinic (ALA) acid and porphobilinogen (PBG) not seen?&#10;A)acute intermittent porphyria&#10;B)variegate porphyria&#10;C)hereditary coproporphyria&#10;D)porphyria cutanea tarda

Accepted Answer

Porphyria cutanea tarda does not show an increase in ALA and PBG.The enzyme that is deficient in this porphyria is uroporphyrinogen decarboxylase, which would lead to an increase of urinary uroporphyrin but not urinary ALA and PBG.

Question 8

Iron in the Fe&#178;&#8314; state is known as ______ iron, and iron in the Fe&#179;&#8314; state is known as ______ iron.The conversion of Fe&#179;&#8314; to Fe&#178;&#8314; is known as ______.&#10;A)ferric, ferrous, oxidation&#10;B)ferric, ferrous, reduction&#10;C)ferrous, ferric, oxidation&#10;D)ferrous, ferric, reduction

Accepted Answer

Fe²⁺ is known as ferrous iron.Fe³⁺ is known as ferric iron.Most dietary iron is in the ferric state and must be converted to the ferrous state before it can enter the intestinal cell.Ferric reductase is the enzyme responsible for the reduction of ferric iron to ferrous iron.

Question 9

In hepatic porphyria cutanea tarda, which of the following will show the greatest increase?&#10;A)urinary porphobilinogen&#10;B)urinary uroporphyrin&#10;C)fecal coproporphyrin&#10;D)fecal protoporphyrin

Accepted Answer

Hepatic porphyria cutanea tarda is caused by a partial deficiency of uroporphyrinogen decarboxylase.As a result of this deficiency, there will be an accumulation of uroporphyrinogen, which will readily oxidize to uroporphyrin.Uroporphyrin, being relatively polar, will be excreted into the urine.

Question 10

Percent saturation is a useful expression that relates:&#10;A)iron to ferritin&#10;B)iron to transferrin&#10;C)iron to hemosiderin&#10;D)iron to total iron stores

Accepted Answer

Percent saturation is calculated by: (serum iron/TIBC) × 100%.TIBC serves as an indirect measure of transferrin, and the percent saturation calculation serves as an indicator of the degree of iron saturation of transferrin.

Question 11

Free erythrocyte protoporphyrin is somewhat of a misnomer.This form of protoporphyrin that is found elevated in the erythrocyte in certain disorders is actually bound to ________ instead of being free in the erythrocyte.

A)calcium
B)magnesium
C)albumin
D)zinc

Accepted Answer

The answer of Free erythrocyte protoporphyrin is somewhat of a...

Question 12

Data below provide laboratory evidence of which pathological condition?
Red cell morphology - hypochromia, microcytosis
Serum iron - increased
TIBC - normal
Percent saturation - increased
Serum ferritin - increased

A)iron deficiency anemia
B)thalassemia
C)sideroblastic anemia
D)autoimmune hemolytic anemia

Accepted Answer

The answer of Data below provide laboratory evidence of which...

Question 13

Which of the following would be expected in association with kidney disease?&#10;A)increased serum iron&#10;B)decreased TIBC&#10;C)both a and b&#10;D)neither a or b

Accepted Answer

The answer of Which of the following would be expected...

Question 14

It is known that porphyrins are colored compounds, whereas porphyrinogens are colorless compounds.What is the chemical difference between porphyrins and porphyrinogens that accounts for this difference?

A)the degree of saturation
B)the degree of hydrophobicity
C)the degree of hydrophilicity
D)the presence of multiple nitrogen atoms

Accepted Answer

The answer of It is known that porphyrins are colored...

Question 15

Which of the following is considered the most appropriate method for quantifying porphyrins in blood or urine?&#10;A)spectrophotometry&#10;B)nephelometry&#10;C)turbidity&#10;D)fluorometry

Accepted Answer

The answer of Which of the following is considered the...

Question 16

The following data provide laboratory evidence of which disorder of porphyrin metabolism?
Urinary δ-aminolevulinic acid (ALA) - elevated
Urinary porphobilinogen (PBG) - normal
Free erythrocyte protoporphyrin (zinc protoporphyrin) - elevated

A)acute intermittent porphyria
B)porphyria cutanea tarda
C)hereditary coproporphyria
D)lead poisoning

Accepted Answer

The answer of The following data provide laboratory evidence of...

Question 17

The rate-limiting step in heme synthesis in the liver is regulated by which enzyme?&#10;A)ALA synthase&#10;B)ALA dehydratase&#10;C)PBG deaminase&#10;D)Ferrochelatase

Accepted Answer

The answer of The rate-limiting step in heme synthesis in...

Question 18

Data below provide laboratory evidence of which pathological condition?
Red cell morphology - hypochromia, microcytosis
Serum iron - increased
TIBC - normal
Percent saturation - increased
Serum ferritin - increased

A)iron deficiency anemia
B)thalassemia
C)sideroblastic anemia
D)autoimmune hemolytic anemia

Accepted Answer

The answer of Data below provide laboratory evidence of which...

Deck 39: Iron and Porphyrin Metabolism