Why Are the Ends of Microfilaments and Microtubules Called "Plus

question 75

Multiple Choice

Why are the ends of microfilaments and microtubules called "plus ends" and "minus ends"?

• A)Because monomers are added more quickly to one end (the "plus end")than they are to the other end (the "minus end").
• B)Because polymerization occurs at one end (the "plus end")and depolymerization occurs at the other end (the "minus end").
• C)Because monomers can be added to one end only (the "plus end"), and can only be removed from the other end (the "minus end").
• D)Because the actin and tubulin monomers that make up microfilaments and microtubules have evolved more rapidly than most other proteins.