Chapter 17. Actin Treadmilling

Animation Activities

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Animation Activity 17-10: Actin Treadmilling

1.

Polymerization of actin in vitro illustrates several import properties of the polymerization process that occurs in cells. Which of the following is NOT true about G-actin monomer polymerization into F-actin filaments in vitro?

The critical concentration is the G-actin concentration at which the rate of addition is equal to the rate of loss of subunits from one end of the actin filament

During the elongation phase, G-actin monomers add only to the (+) end of each actin filament.

During the steady state phase, the total amount of F-actin does not change, but G-actins continue to add to and dissociate from both ends.

During the steady state phase, actin is at a specific concentration, known as the critical concentration, and is always disassembled in the G-actin form despite continual addition and loss of actin monomers at both ends of each actin filament.

All of the above statements are true.

Correct.

Incorrect.

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2.

In an F-actin filament, the _________ ends of the subunits face the (–) end of the filament and the _________ ends face the (+) end.

clefted; rounded

rounded; clefted

polymerizing; depolymerizing

depolymerizing; polymerizing

growing; shrinking

Correct.

Incorrect.

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3.

If G-actin is continuously added to a test tube until the actin concentration exceeds the critical concentration (Cc), _______

the amount of actin exceeding the Cc polymerizes into F-actin.

approximately 33% of the actin exceeding the Cc polymerizes into F-actin and 66% adds to the unpolymerized G-actin pool.

approximately 50% of the actin exceeding the Cc polymerizes into F-actin and 50% adds to the unpolymerized G-actin pool.

approximately 66% of the actin exceeding the Cc polymerizes into F-actin and 33% adds to the unpolymerized G-actin pool.

It is impossible to predict based on the information given.

Correct.

Incorrect.

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4.

Although the rate of actin monomer dissociation (off rate) from each end of a filament is similar, the (+) end has a lower critical concentration (Cc) than the (–) end because __________.

the rate of association (on rate) is greater at the (–) end than at the (+) end.

the rate of association (on rate) is greater at the (+) end than at the (–) end.

the rate of ATP hydrolysis is greater at the (+) end than at the (–) end.

an actin monomer can treadmill from the (–) end of the filament to the (+) end.

the rate of ATP hydrolysis is greater at the (–) end than at the (+) end.

Correct.

Incorrect.

Try Again.

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Chapter 17. Actin Treadmilling

Introduction

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