$$n \times \text{G-actin} \rightarrow \text{F-actin}$$

Question 1

Which of the following statements best describes the role of microfilaments in eukaryotic cells?

Accepted Answer

Microfilaments are involved in cell migration, amoeboid movement, and cytoplasmic streaming in all eukaryotic cells.

Question 2

Which protein is the main component of microfilaments, and what is its polymerized form called?

Accepted Answer

Actin; F-actin

Question 3

What is the primary difference between G-actin and F-actin?

Accepted Answer

G-actin is a globular monomer, while F-actin is a filamentous polymer.

Question 4

Which end of a microfilament is referred to as the 'barbed' end, and why is this terminology used?

Accepted Answer

The plus end, because it is the site of rapid addition of actin monomers.

Question 5

Which of the following drugs stabilizes microfilaments and prevents their depolymerization?

Accepted Answer

Phalloidin

Question 6

A researcher treats cells with latrunculin A. What is the expected effect on actin microfilaments?

Accepted Answer

Actin monomers will be sequestered, preventing their addition to microfilaments.

Question 7

Which of the following best explains the polarity of microfilaments?

Accepted Answer

The plus end of the microfilament grows more rapidly than the minus end.

Question 8

Cells that crawl have leading-edge structures called lamellipodia and filopodia. What is the main difference between these two structures?

Accepted Answer

Lamellipodia are branched networks of actin, while filopodia are tightly bundled linear actin filaments.

Question 9

Which protein is known to sever actin filaments and cap the newly exposed plus ends, preventing further polymerization?

Accepted Answer

Gelsolin

Question 10

What is the function of the terminal web in intestinal epithelial cells?

Accepted Answer

It anchors microfilament bundles at the base of microvilli and connects them to the plasma membrane.

Question 11

Which equation best represents the polymerization of actin monomers into filaments?

Accepted Answer

$$n 	imes 	ext{G-actin} ightarrow 	ext{F-actin}$$

Question 12

If the concentration of ATP-bound G-actin is high in a cell, what is the expected outcome?

Accepted Answer

Microfilaments will assemble until the G-actin is limiting.

Question 13

Which actin-binding protein is important for crosslinking actin filaments into loose networks?

Accepted Answer

Filamin

Question 14

Microvilli in intestinal cells increase the surface area for absorption. What is the structural core of a microvillus composed of?

Accepted Answer

A tight bundle of microfilaments with the ends pointed toward the tip

Question 15

Which of the following proteins competes with thymosin for G-actin binding and promotes actin polymerization?

Accepted Answer

Profilin

Question 16

What is the role of capping proteins in actin filament dynamics?

Accepted Answer

They prevent further loss or addition of subunits at the ends of microfilaments.

Question 17

Which of the following is a real-world example of a drug that binds tightly to F-actin and is derived from death cap mushrooms?

Accepted Answer

Phalloidin

Question 18

During cell migration, what drives the forward movement of the leading edge?

Accepted Answer

Polymerization of actin at the leading edge

Question 19

Which of the following proteins is involved in connecting microfilaments to the plasma membrane and exerting force during cytokinesis?

Accepted Answer

Band 4.1

Question 20

Which statement best describes the organization of actin filaments in the cell cortex?

Accepted Answer

Actin filaments in the cortex form a 3D gel-like network through crosslinking proteins.

Microfilaments and Actin Cytoskeleton: Structure, Function, and Regulation

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