Actin filaments will ?Yes, that’s correct!
a. undergo treadmilling in a test tube
b. undergo treadmilling in a living cell
c. never reach equilibrium
d. Two of the above
e. None of the above
f. I don’t know the answer
The correct answer and explanation is:
The correct answer is d. Two of the above.
Explanation:
Actin filaments, also known as microfilaments, are one of the key components of the cytoskeleton in eukaryotic cells. These filaments are highly dynamic and undergo a process called “treadmilling.” This refers to the continuous addition of actin subunits at one end of the filament (the plus or barbed end) and their removal at the other end (the minus or pointed end). This process allows the filament to maintain a constant length while still exhibiting dynamic behavior.
Treadmilling in a test tube: Actin filaments in vitro (in a test tube) can indeed undergo treadmilling, as long as the conditions such as the presence of ATP and actin monomers are favorable. When actin filaments are placed in a test tube under appropriate conditions, they can polymerize and depolymerize at different rates at the two ends, leading to treadmilling behavior.
Treadmilling in a living cell: In a living cell, actin filaments also undergo treadmilling. This is crucial for processes like cell movement, shape maintenance, and division. In the cell, treadmilling occurs in a controlled environment where actin-binding proteins regulate polymerization and depolymerization. For example, the leading edge of a migrating cell often shows polymerization of actin filaments, while at the trailing edge, depolymerization occurs. This continuous turnover allows the cell to “push” forward while maintaining structural integrity.
Never reaching equilibrium: Actin filaments do not typically reach equilibrium. In both in vitro and in vivo conditions, treadmilling ensures that the actin filaments are continuously cycling through polymerization and depolymerization, which prevents them from reaching a static equilibrium. This dynamic nature is essential for the cellular functions that depend on the cytoskeleton.
In conclusion, actin filaments can undergo treadmilling in both a test tube and in living cells, which is why the correct answer is d. Two of the above.