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      which of the following apply to microtubules, which to microfilaments and which to both?
      1. all the nucleotide-binding sites point the same direction
      2. monomers bind GTP
      3. dimers polymerize into protofilaments that they associate side by side
      4. structure is adouble chain of subunits
      5. fibers polymerize and depolymerize quickly
      6. 13 protofilaments associate to form a hollow tube
      7. monomers bind ATP
      8. polymer of globular subunits

      i thought that 1,2,5, and 6 are microtubules.
      3,4, and 7microfilaments
      8 is both

      However, my answer is incorrect. The hints given are:

      Consider the name "microtubule". would you expect the shape to be thin or thick and tube like.

      microfilament composed of globular monomeric actin and microtubulin composed of alpha-tubulin and beta-tubulin. consider the shape of alpha tubulin and beta tubulin. ATP and GTP are nucleotides.

      For an actin or tubulin monomer, the end with the nucleotide-binding site is the (-) end. As a result of assembly of the monomers, each filament has a (+) end and a (-) end.

      Both microtubules and microfilaments can "trendmill" meaning that subunits are added at the (+) end at the same rate as subunits are lost from the (-) end. consider this regarding microfilament and microtubule assembly and disassembly.

      Thank you so much for your help! 🙂

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