Microtubules

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Questions and Answers

What are the major structural elements of the cytoskeleton?

  • Microfilaments, microtubules, intermediate filaments (correct)
  • Ribosomes, endoplasmic reticulum, Golgi apparatus
  • Lysosomes, peroxisomes, vacuoles
  • Chloroplasts, mitochondria, nucleus

What are the functions of the cytoskeleton?

  • Cell movement and division (correct)
  • DNA replication and repair
  • Protein synthesis and packaging
  • Energy production and storage

What are the bacterial cytoskeletal elements structurally similar to those in eukaryotes?

  • Peptidoglycan and lipopolysaccharides
  • Actin-like MreB and tubulin-like FtsZ (correct)
  • Chlorophyll and carotenoids
  • Nucleoid and plasmids

Which proteins use ATP to drive vesicle or organelle transport or to generate sliding forces between microtubules?

<p>Microtubule-binding proteins (B)</p> Signup and view all the answers

Which proteins bind at regular intervals along a microtubule wall, allowing for interaction with other cellular structures and filaments?

<p>Microtubule-stabilizing/bundling proteins (C)</p> Signup and view all the answers

Which proteins promote depolarization of microtubules?

<p>Catastrophins (C)</p> Signup and view all the answers

Which proteins bind to tubulin heterodimers and prevent their polymerization?

<p>Stathmin/Op18 (D)</p> Signup and view all the answers

What gives microtubules inherent polarity with plus and minus ends?

<p>Protofilaments made of α and β tubulin heterodimers (D)</p> Signup and view all the answers

What contributes to the dynamic instability of microtubules, leading to periods of growth, shrinkage, catastrophe, and rescue?

<p>GTP hydrolysis (C)</p> Signup and view all the answers

What nucleates the assembly of new microtubules?

<p>γ-tubulin (B)</p> Signup and view all the answers

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Study Notes

Microtubules: Structure, Assembly, and Function

  • Microtubules are the largest structural elements of the cytoskeleton, involved in various cellular functions.
  • There are two types of microtubules: cytoplasmic and nuclear, responsible for different functions such as maintaining axons and cell shape, and forming spindles.
  • Microtubules are composed of tubulin heterodimers, forming straight, hollow cylinders of varied lengths.
  • Protofilaments, made of α and β tubulin heterodimers, give microtubules inherent polarity with plus and minus ends.
  • Microtubules form through the reversible polymerization of tubulin dimers in the presence of GTP and Mg2+, with distinct lag and elongation phases.
  • Microtubule assembly depends on the concentration of tubulin dimers and the critical concentration, leading to growth or disassembly.
  • The plus end of microtubules grows faster due to the addition of tubulin dimers, while treadmilling occurs when free tubulin concentration varies at the plus and minus ends.
  • GTP hydrolysis contributes to the dynamic instability of microtubules, leading to periods of growth, shrinkage, catastrophe, and rescue.
  • Microtubules originate from microtubule-organizing centers (MTOCs) containing γ-tubulin, which nucleates the assembly of new microtubules.
  • MTOCs organize and polarize microtubules within cells, with the minus ends anchored in the MTOC, leading to dynamic growth and shrinkage at the plus ends.
  • Centrosomes, containing γ-tubulin ring complexes, are MTOCs that nucleate the assembly of new microtubules away from the centrosome.
  • Loss of γ-TuRCs prevents a cell from nucleating microtubules, impacting cellular functions.

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