Actin filaments have polarity. This means that the two ends can be identified due to structural differences. The plus end is the end to which subunits are added more rapidly, or the end of polymerization. Which of the following would enable you to identify the plus end of actin filaments?
A) adding radiolabeled actin subunits to a mixture of actin filaments in which conditions are favorable for polymerization
B) adding radiolabeled actin subunits to a mixture of actin filaments in which conditions favor depolymerization
C) determining the ionic charge of the ends of the actin filaments

Question

Quizplus · Accepted Answer

Adding radiolabeled actin subunits to a mixture of actin filaments in which conditions are favorable for polymerization would enable you to identify the plus end of actin filaments, as this is the end where subunits are added more rapidly, leading to an increase in radioactivity at this end. Adding radiolabeled actin subunits to a mixture of actin filaments in which conditions favor depolymerization would not help identify the plus end as subunits would be removed equally from both ends, and determining the ionic charge of the ends of the actin filaments would not necessarily correlate with the rate of subunit addition.

Actin Filaments Have Polarity