microtubule

Examples of microtubule in the following topics:

• Intermediate Filaments and Microtubules

  • As their name implies, microtubules are small hollow tubes.
  • Microtubules are the largest element of the cytoskeleton.
  • Like microfilaments, microtubules can dissolve and reform quickly.
  • In animal cells, the centrosome is the microtubule-organizing center.
  • This transmission electron micrograph of two flagella shows the 9 + 2 array of microtubules: nine microtubule doublets surround a single microtubule doublet.

• Centrosome

  • Fungi and plants use other MTOC structures to organize their microtubules.
  • In general, each centriole of the centrosome is based on a nine triplet microtubule assembled in a cartwheel structure.
  • The PCM contains proteins responsible for microtubule nucleation and anchoring.
  • Acentrosomal cells lack radial arrays of astral microtubules.
  • Microtubules are anchored at the centrosomes.

• Meiosis II

  • Each sister chromatid forms an individual kinetochore that attaches to microtubules from opposite poles.
  • The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles.
  • Non-kinetochore microtubules elongate the cell .
  • In prometaphase I, microtubules attach to the fused kinetochores of homologous chromosomes, and the homologous chromosomes are arranged at the midpoint of the cell in metaphase I.
  • In prometaphase II, microtubules attach to the kinetochores of sister chromatids, and the sister chromatids are arranged at the midpoint of the cells in metaphase II.

• The Mitotic Phase and the G0 Phase

  • Microtubules that will eventually form the mitotic spindle extend between the centrosomes, pushing them farther apart as the microtubule fibers lengthen.
  • The mitotic spindle continues to develop as more microtubules assemble and stretch across the length of the former nuclear area.
  • The proteins of the kinetochore attract and bind mitotic spindle microtubules.
  • Each chromatid, now called a chromosome, is pulled rapidly toward the centrosome to which its microtubule is attached.
  • During prometaphase, mitotic spindle microtubules from opposite poles attach to each sister chromatid at the kinetochore.

• Meiosis I

  • The centrosomes, which are the structures that organize the microtubules of the meiotic spindle, also replicate.
  • Microtubules grow from centrosomes placed at opposite poles of the cell.
  • The microtubules move toward the middle of the cell and attach to one of the two fused homologous chromosomes at the kinetochores.
  • In anaphase I, the microtubules pull the attached chromosomes apart.
  • The chiasmata are broken in anaphase I as the microtubules attached to the fused kinetochores pull the homologous chromosomes apart.

• Comparing Plant and Animal Cells

  • While both animal and plant cells have microtubule organizing centers (MTOCs), animal cells also have centrioles associated with the MTOC: a complex called the centrosome.
  • The centrosome is a microtubule-organizing center found near the nuclei of animal cells.
  • Each centriole is a cylinder of nine triplets of microtubules.
  • Each centriole is a cylinder made up of nine triplets of microtubules.
  • Nontubulin proteins (indicated by the green lines) hold the microtubule triplets together.

• Binary Fission

  • However, the FtsZ protein that plays such a vital role in prokaryotic cytokinesis is structurally and functionally very similar to tubulin, the building block of the microtubules that make up the mitotic spindle fibers that are necessary for eukaryotes.
  • FtsZ proteins can form filaments, rings, and other three-dimensional structures that resemble the way tubulin forms microtubules, centrioles, and various cytoskeletal components.

• Fluorescence Microscopy

  • Nuclei are stained blue with DAPI, microtubules are stained green by an antibody bound to FITC and actin filaments are labelled red with phalloidin bound to TRITC.

• Rhizaria

  • Radiolarians display needle-like pseudopods that are supported by microtubules which radiate outward from the cell bodies of these protists and function to catch food particles.

• Sperm