Q: Which of the following equations best represents the relationship between the critical concentration ($$C_c) $$for microtubule assembly and tubulin concentration ($$[Tubulin]) $$for treadmilling to occur?

$$[Tubulin] \u003e C_{c,+}$$ \,\text{and}\, [Tubulin] \u003c C_{c,-}$

Q: Which equation correctly represents the phosphorylation of Rb by G1 Cdk–cyclin, leading to the release of E2F and entry into S phase?

$$\text{Rb} + \text{Cdk–cyclin}_{G1} \rightarrow \text{Rb-P} + \text{E2F}$$

Question 1

Which cytoskeletal element is primarily responsible for maintaining the rod shape of bacterial cells and is functionally analogous to actin in eukaryotes?

Accepted Answer

MreB

Question 2

A scientist is studying a drug that binds to assembled microtubules and prevents their disassembly, thereby arresting cells in mitosis. Which drug is most likely being used?

Accepted Answer

Paclitaxel (Taxol)

Question 3

Which protein is the main building block of microfilaments, and what is the difference between its G and F forms?

Accepted Answer

Actin; G-actin is the monomer, F-actin is the polymer

Question 4

A patient with muscular dystrophy is found to have a mutation in a protein that links the muscle cell cytoskeleton to the extracellular matrix. Which protein is most likely affected?

Accepted Answer

Dystrophin

Question 5

Which of the following best describes the mechanism by which the GTP cap stabilizes microtubule growth?

Accepted Answer

GTP-tubulin at the plus end forms a cap that prevents rapid depolymerization; loss of the cap leads to catastrophe.

Question 6

Which cell junction is responsible for forming a permeability barrier in epithelial tissues, preventing paracellular transport?

Accepted Answer

Tight junction

Question 7

A researcher observes that cells in culture undergo apoptosis when they lose attachment to the extracellular matrix. Which protein family mediates this anchorage-dependent survival signal?

Accepted Answer

Integrins

Question 8

Which of the following is the most abundant structural protein in the animal extracellular matrix, providing tensile strength?

Accepted Answer

Collagen

Question 9

During mitosis, which structure provides the attachment site for spindle microtubules, ensuring accurate chromosome segregation?

Accepted Answer

Kinetochore

Question 10

Which checkpoint ensures that all chromosomes are properly attached to the spindle before sister chromatids separate?

Accepted Answer

Metaphase–anaphase transition (spindle checkpoint)

Question 11

A cell is exposed to DNA-damaging agents. Which protein acts as a 'guardian of the genome' by inducing cell cycle arrest or apoptosis?

Accepted Answer

p53

Question 12

Which signaling pathway is directly activated by growth factors, leading to phosphorylation of MAPKs and transcription of genes promoting cell cycle progression?

Accepted Answer

Ras–MAPK pathway

Question 13

Which of the following equations best represents the relationship between the critical concentration ($$C_c) $$for microtubule assembly and tubulin concentration ($$[Tubulin]) $$for treadmilling to occur?

Accepted Answer

$$[Tubulin] \u003e C_{c,+}$$ \,	ext{and}\, [Tubulin] \u003c C_{c,-}$

Question 14

Which class of intermediate filaments is found in epithelial cells and provides mechanical strength to tissues such as skin, hair, and nails?

Accepted Answer

Class I–II: Keratins

Question 15

Which molecule is responsible for the stretch and recoil properties of the extracellular matrix in tissues such as lungs and arteries?

Accepted Answer

Elastin

Question 16

Which of the following best describes the process of apoptosis compared to necrosis?

Accepted Answer

Apoptosis is an orderly process involving caspase activation and cell shrinkage; necrosis is uncontrolled cell rupture and inflammation.

Question 17

Which equation correctly represents the phosphorylation of Rb by G1 Cdk–cyclin, leading to the release of E2F and entry into S phase?

Accepted Answer

$$	ext{Rb} + 	ext{Cdk–cyclin}_{G1} ightarrow 	ext{Rb-P} + 	ext{E2F}$$

Question 18

Which plant cell structure is functionally analogous to animal gap junctions, allowing direct cytoplasmic communication between adjacent cells?

Accepted Answer

Plasmodesmata

Question 19

A cell is exposed to TGFβ, which activates Smad proteins and induces expression of Cdk inhibitors. What is the most likely outcome?

Accepted Answer

Cell cycle progression is inhibited

Question 20

Which of the following best describes the difference between mitosis and cytokinesis?

Accepted Answer

Mitosis is nuclear division; cytokinesis is cytoplasmic division.

Cell Biology Exam 3 Study Guide: Cytoskeleton, Cell Junctions, and Cell Cycle

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