Cellular Transport And Signaling Pathways Practice Test Practice Tests

Question 1

A protein is glycosylated in the ER and its oligosaccharide side chain contains 14 sugar residues. If each sugar residue contributes approximately 0.2 kDa to the molecular weight, what is the approximate increase in molecular weight due to glycosylation?

Accepted Answer

C. 2.8 kDa

Answer

A. 1.4 kDa

Answer

B. 2.0 kDa

Answer

D. 3.6 kDa

Question 2

Dynamin is a GTPase involved in vesicle formation. If the rate of vesicle scission is directly proportional to the GTP hydrolysis rate of dynamin, and the GTP hydrolysis rate is 5 GTP molecules per second per dynamin molecule, how many GTP molecules are hydrolyzed to pinch off a vesicle if 20 dynamin molecules are involved?

Accepted Answer

100 GTP molecules

Question 3

Which of the following protein coats are involved in vesicular transport and what are their primary functions?

Answer

A. COPII: Mediates anterograde transport from the ER to the Golgi.

Answer

B. COPI: Involved in retrograde transport from the Golgi back to the ER.

Answer

C. Clathrin: Participates in endocytosis at the plasma membrane and transport between the Golgi and endosomes.

Answer

D. KDEL: ER retention signal

Question 4

The unfolded protein response (UPR) decreases the production of chaperones and increases ER protein synthesis to manage misfolded proteins in the ER.

Accepted Answer

True

Answer

False

Question 5

If the pH of a lysosome is 5.0, and the pH of the cytosol is 7.2, what is the proton concentration gradient ([H+]lysosome / [H+]cytosol) between the lysosome and the cytosol? (Note: pH = -log[H+])

Accepted Answer

B. Approximately 158

Answer

A. Approximately 22

Answer

C. Approximately 220

Answer

D. Approximately 500

Question 6

A cell internalizes 1000 receptors via receptor-mediated endocytosis every hour. If 20% of these receptors are degraded in lysosomes and the rest are recycled back to the plasma membrane, how many receptors are recycled per hour?

Accepted Answer

800 receptors

Question 7

Which of the following are functions of glycosylation in the endoplasmic reticulum (ER)?

Answer

A. Protects proteins from degradation.

Answer

B. Helps with proper protein folding.

Answer

C. Acts as a transport signal.

Answer

D. Directly involved in ATP production.

Question 8

Phagocytosis involves the uptake of fluids and small molecules into small vesicles, while pinocytosis involves the uptake of large particles into large vesicles.

Accepted Answer

True

Answer

False

Question 9

A cell signaling pathway involves a GPCR. After ligand binding, the $α$ subunit of the G protein exchanges GDP for GTP. If a non-hydrolyzable analog of GTP is added to the system, what is the most likely outcome?

Accepted Answer

C. The $α$ subunit will remain active, continuously stimulating downstream signaling pathways.

Answer

A. The $α$ subunit will immediately become inactive.

Answer

B. The $βγ$ complex will be unable to interact with downstream targets.

Answer

D. The GPCR will be unable to bind further ligands.

Question 10

A researcher is studying a novel GPCR signaling pathway. They observe that upon ligand binding, the intracellular concentration of cAMP increases. Describe the steps involved in this process, including the specific G protein subunit and enzyme involved.

Accepted Answer

Ligand binding activates the GPCR, which then activates a Gs protein. The $α_s$ subunit of the Gs protein activates adenylyl cyclase. Adenylyl cyclase then converts ATP to cAMP, increasing the intracellular cAMP concentration.

Question 11

Trans-autophosphorylation of receptor tyrosine kinases (RTKs) is a process where a single RTK phosphorylates itself upon ligand binding.

Accepted Answer

True

Answer

False

Question 12

Consider an enzyme-coupled receptor that, upon activation, phosphorylates a target protein, increasing its activity. If a phosphatase inhibitor is introduced into the cell, what is the expected effect on the activity of the target protein?

Accepted Answer

B. The activity of the target protein will remain elevated for a longer duration.

Answer

A. The activity of the target protein will decrease.

Answer

C. The enzyme-coupled receptor will be unable to phosphorylate the target protein.

Answer

D. There will be no change in the activity of the target protein.

Question 13

Which of the following are characteristics of G protein-coupled receptors (GPCRs)?

Answer

A. They possess seven transmembrane domains.

Answer

B. They directly phosphorylate target proteins.

Answer

C. They interact with heterotrimeric G proteins.

Answer

D. They can act as guanine nucleotide exchange factors (GEFs).

Question 14

A researcher is studying cell signaling and observes that a particular growth factor stimulates cell proliferation. They determine that the receptor involved is an RTK. Describe the process of receptor activation and downstream signaling following growth factor binding to the RTK.

Accepted Answer

Growth factor binding induces RTK dimerization. The RTK dimer undergoes trans-autophosphorylation. Phosphorylated tyrosines serve as docking sites for intracellular signaling proteins, initiating downstream signaling cascades that promote cell proliferation.

Question 15

In the cAMP signaling pathway, if the concentration of ATP is 5 mM and adenylyl cyclase converts 2% of ATP to cAMP per second, what is the rate of cAMP production in $\mu$M/s? Assume the volume is 1 liter.

Accepted Answer

100 $\mu$M/s

Answer

10 $\mu$M/s

Answer

50 $\mu$M/s

Answer

200 $\mu$M/s

Question 16

If a cell's cAMP phosphodiesterase activity is inhibited, and the rate of cAMP production by adenylyl cyclase remains constant at 25 $\mu$M/s, what will happen to the cAMP concentration over time? Explain your answer.

Accepted Answer

The cAMP concentration will increase over time because the rate of production exceeds the rate of degradation.

Question 17

In the IP3 and DAG signaling pathway, if phospholipase C cleaves 1000 molecules of inositol phospholipid, and each IP3 molecule opens one Ca2+ channel on the ER, how many Ca2+ ions are released into the cytoplasm, assuming each channel releases 500 Ca2+ ions?

Accepted Answer

500,000 Ca2+ ions

Answer

1,000 Ca2+ ions

Answer

50,000 Ca2+ ions

Answer

100,000 Ca2+ ions

Question 18

Activation of protein kinase C (PKC) by DAG directly leads to the phosphorylation of downstream target proteins, altering their activity.

Accepted Answer

True

Answer

False

Question 19

If a mutation causes Ras to be constitutively active (always bound to GTP), which of the following is the MOST likely outcome?

Accepted Answer

Uncontrolled cell growth and proliferation

Answer

Decreased cell growth and proliferation

Answer

Increased apoptosis (programmed cell death)

Answer

Cell cycle arrest

Question 20

Which of the following are direct consequences of PI 3-kinase activation?

Answer

Activation of adenylyl cyclase

Answer

Production of phosphorylated inositol phospholipids

Answer

Activation of Akt protein kinase

Answer

Inhibition of phospholipase C

Cellular Transport And Signaling Pathways Practice Test Practice Tests

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Cellular Transport and Signaling Pathways Practice Test

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