Question 1

You wish to target a purified enzyme to the lysosomes of macrophages.How might you accomplish this?

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Question 2

In carrying out a pulse-chase experiment,radiolabel appears first over the ER in the basal portion of the cell.It moves next to the Golgi apparatus located centrally.Next,the radiolabel appears in the cell's apical region near a number of small cytoplasmic vesicles.What kind of cell is this?

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Question 3

Approaches other than enzyme replacement therapy for treatment of lysosomal storage diseases have shown some promise.What are they and how do they work?

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Question 4

The mRNA for a well-known secretory protein is isolated and placed in a test tube in the presence of all the substances required for in vitro protein synthesis.The sequence of the protein produced in vitro is then compared to the sequence of the purified secretory protein.The sequences of the two proteins are not the same.What is the explanation?

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Question 5

What is responsible for the deficiency in I-cell disease patients in which the lysosomal enzymes do not carry the normal mannose phosphate residues that target them to lysosomes?

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Question 6

Why does glucocerebrosidase taken into macrophages by receptor-mediated endocytosis end up in lysosomes?
A)The enzyme travels through the cytoplasm to get to lysosomes.
B)The enzyme denatures and then goes through a channel into lysosomes.
C)Lysosomes are the natural target of enzymes taken into macrophages by endocytosis.
D)Lysosomes adsorb glucocerebrosidase to their surfaces.
E)Lysosomes pick up the enzyme from mitochondria.

Accepted Answer

Lysosomes are the natural target of enzymes taken into macrophages by endocytosis. Macrophages are specialized cells that engulf and break down bacteria, dead cells, and other debris in the body. When they take up the enzyme glucocerebrosidase by receptor-mediated endocytosis, it is delivered to lysosomes, which are rich in enzymes that break down biological molecules. Glucocerebrosidase is used by lysosomes to break down a fatty substance called glucocerebroside, which is a normal component of cell membranes. When there is a deficiency in glucocerebrosidase activity, as in the case of Gaucher disease, glucocerebroside accumulates in lysosomes and causes damage to various organs in the body.

Question 7

Why does targeting glucocerebrosidase to lysosomes in macrophages serve as a treatment for Gaucher's disease?
A)Glucocerebrosidase is normally denatured in the lysosomes.
B)Glucocerebrosidase is delivered to the precise sites in the cell where the deficiency is manifested,thus correcting the deficit.
C)Glucocerebrosidase denatures the cytoplasm from its location in the lysosomes correcting the deficit.
D)Glucocerebrosidase binds to the outer lysosome surface and breaks down glycogen in the cytoplasm.
E)Glucocerbrosidase is supposed to digest most of the enzymes in the lysosome.

Accepted Answer

Gaucher's disease is caused by a deficiency of glucocerebrosidase, an enzyme that normally breaks down a fatty substance called glucocerebroside in lysosomes. Without this enzyme, glucocerebroside accumulates in the lysosomes of macrophages, leading to cell damage and dysfunction. Targeting glucocerebrosidase to lysosomes in macrophages can serve as a treatment because it delivers the enzyme to the specific location where the deficiency is manifested, allowing it to break down the accumulated glucocerebroside and correct the deficit.

Question 8

A scientist isolates two specific mRNAs.One codes for the enzyme fowlase,an enzyme that is involved in digestion in chickadees;the other codes for the quail enzyme quailase that is involved in cellular carbohydrate metabolism.Both mRNAs are placed in a test tube with RER vesicles stripped of their ribosomes,free ribosomes and precursors for protein synthesis.When the protein synthesis reaction is complete,fowlase is found inside the vesicles;quailase is found in the liquid portion of the test tube outside the vesicles.What can one conclude about the two proteins?

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Question 9

You homogenize a cell and isolate from it vesicles derived from the endoplasmic reticulum.When their biochemistry is analyzed,they are found to have the ability to synthesize testosterone.From what type of ER are they derived?

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Question 10

Explain how lysosomes become bloated in patients who suffer from I-cell disease.

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Question 11

You homogenize a liver cell and isolate from it vesicles derived from the endoplasmic reticulum.When their biochemistry is analyzed,they are found to contain oxygenases.From what type of ER are they derived?

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Question 12

A tissue that secretes a number of proteins is exposed in culture to radiolabeled amino acids for a very short period of time and then fixed immediately and prepared for autoradiography.What is seen after the autoradiograms are prepared?

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Question 13

Treatment of lysosomal storage disorders with substrate reduction therapy involves _______.
A)targeting functional copies of the missing enzyme to the cell sites where the deficiency is manifested
B)targeting mutant copies of the missing enzyme to the cell sites where the deficiency is manifested
C)targeting functional copies of another enzyme to the cell sites where the deficiency is manifested
D)administration of small molecular weight drugs to inhibit the synthesis of the substances that accumulate in the disease
E)administration of large molecular weight drugs to inhibit the synthesis of the substances that accumulate in the disease

Accepted Answer

Substrate reduction therapy involves administration of small molecular weight drugs to inhibit the synthesis of the substances that accumulate in the disease. This approach reduces the amount of substrate that needs to be degraded by the missing enzyme, thereby slowing or preventing disease progression. It does not involve targeting functional or mutant copies of the missing enzyme or another enzyme to cell sites where deficiency is manifested, nor does it involve administration of large molecular weight drugs.

Question 14

Radioactive phospholipid precursors are exposed to growing cells in a brief pulse.After a chase with nonlabeled phospholipid precursors,it is clear that the label appears first over the endoplasmic reticulum.Some time later,the label appears in the cell membrane after being seen in the Golgi complex and cytoplasmic vesicles.To what conclusion do the data lead you?

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Question 15

What is a lysosomal storage disease?

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Question 16

What information does the use of siRNAs provide?

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Question 17

You are observing a cell process in which small vesicles continually merge with the cell membrane.A number of different treatments known to influence the secretion of specific materials seems to have no effect on the process.What type of secretion appears to be occurring?

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Question 18

What is the name of a cellular phenomenon in which cells produce small RNAs that bind to specific mRNAs and inhibit their translation into proteins? What are the small RNAs that bind to these specific mRNAs called?

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Question 19

What recently developed technique allows scientists to follow with their own eyes the dynamic movements of specific proteins as they occur within the living cell?

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Question 20

Treatment of lysosomal storage diseases with enzyme replacement therapy involves _______.
A)targeting functional copies of the missing enzyme to the precise cell sites where the deficiency is manifested
B)targeting mutant copies of the missing enzyme to the cell sites where the deficiency is manifested
C)targeting functional copies of another enzyme to the cell sites where the deficiency is manifested
D)administration of small molecular weight drugs to inhibit the synthesis of substances that accumulate in the disease
E)administration of large molecular weight drugs to inhibit the synthesis of substances that accumulate in the disease

Accepted Answer

Enzyme replacement therapy involves targeting functional copies of the missing enzyme to the precise cell sites where the deficiency is manifested, replacing the deficient enzyme and restoring function. This is done via infusion of the enzyme into the bloodstream, which is then taken up by cells throughout the body, including those affected by the lysosomal storage disease. This approach has been successful in treating several lysosomal storage disorders, such as Gaucher's disease and Fabry disease.

Quiz 8: Cytoplasmic Membrane Systems: Structure, Function, and Membrane Trafficking