$$\text{Rate} = k_{nuc} [\text{G-actin}]^3$$

Question 1

Which of the following best describes the main difference between cytokine receptors and receptor tyrosine kinases (RTKs) in cell signaling?

Accepted Answer

RTKs directly phosphorylate transcription factors, while cytokine receptors activate gene regulatory proteins via JAKs.

Question 2

In the JAK-STAT pathway, what is the role of Janus kinases (JAKs)?

Accepted Answer

JAKs phosphorylate the cytokine receptor, creating docking sites for STATs.

Question 3

Which equation best represents the rate-limiting step in actin filament formation?

Accepted Answer

$$	ext{Rate} = k_{nuc} [	ext{G-actin}]^3$$

Question 4

Which cytoskeletal filament is most concentrated in the cortex of epithelial cells lining the gut?

Accepted Answer

Actin filaments

Question 5

A mutation in the Arp2/3 complex would most likely affect which cellular process?

Accepted Answer

Formation of treelike actin filament webs

Question 6

Which signaling pathway is directly activated by TGF-β receptors at the plasma membrane?

Accepted Answer

Smad-dependent pathway

Question 7

In the ethylene signaling pathway in plants, what happens to EIN3 in the absence of ethylene?

Accepted Answer

EIN3 is ubiquitinated and degraded in proteasomes.

Question 8

Which of the following is a unique feature of plant cell signaling compared to animal cell signaling?

Accepted Answer

Plant cells commonly use serine/threonine kinases as transmembrane receptors.

Question 9

During actin filament treadmilling, which end of the filament typically grows faster?

Accepted Answer

Plus (barbed) end

Question 10

Which equation describes the steady-state concentration of actin monomers during filament polymerization?

Accepted Answer

$$C_c = \frac{k_{off}}{k_{on}}$$

Question 11

Which cytoskeletal filament is responsible for generating the cleavage furrow during cytokinesis?

Accepted Answer

Actin filaments

Question 12

Which of the following best explains why actin filaments are highly dynamic in structure?

Accepted Answer

Actin filaments undergo continuous polymerization and depolymerization regulated by ATP hydrolysis.

Question 13

Which signaling molecule is responsible for the triple response in germinating seedlings encountering an obstacle underground?

Accepted Answer

Ethylene

Question 14

What is the main function of microtubules in polarized epithelial cells?

Accepted Answer

They are attached to organizing centers (MTOCs) and help with intracellular transport.

Question 15

Which protein complex is responsible for nucleating actin filaments and forming branched actin networks?

Accepted Answer

Arp2/3 complex

Question 16

Which of the following is a direct consequence of red light activation of phytochromes in plant cells?

Accepted Answer

Transcription of red-light-responsive genes

Question 17

Which equation best represents the treadmilling rate of actin filaments?

Accepted Answer

$$	ext{Rate}_{treadmilling} = k_{on}^{+} [	ext{G-actin}]_{plus} - k_{off}^{-} [	ext{G-actin}]_{minus}$$

Question 18

Which of the following statements about the divergence of plant and animal lineages is correct?

Accepted Answer

Multicellularity and cell communication evolved independently in plants and animals.

Question 19

Which cytoskeletal filament is most responsible for conferring mechanical strength to cells?

Accepted Answer

Intermediate filaments

Question 20

Which of the following best describes the structural polarity of actin filaments?

Accepted Answer

Actin filaments have a plus (barbed) end and a minus (pointed) end, allowing directional growth.

21: Cell Signaling Pathways and the Cytoskeleton in Eukaryotic Cells

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