The stages, in order

  1. Prophase. The nuclear envelope begins to dissociate, the nucleolus disperses, centrosomes move to opposite poles, and sister chromatids coil tightly enough to become visible under a light microscope.
  2. Prometaphase. The nuclear envelope fragments further and each sister chromatid develops a kinetochore at its centromere. Spindle microtubules bind those kinetochores so that sister kinetochores face opposite poles.
  3. Metaphase. All chromosomes align in the metaphase plate, roughly midway between the poles. Sister chromatids are still held together by cohesin proteins, and the chromosomes are maximally condensed.
  4. Anaphase. Cohesin proteins degrade and the sister chromatids separate at the centromere. Each chromatid, now a chromosome in its own right, is pulled toward the centrosome its microtubule is attached to.
  5. Telophase. Chromosomes reach the opposite poles and decondense back toward chromatin, mitotic spindles depolymerize into tubulin monomers, and nuclear envelopes form around each new set of chromosomes.
  6. Cytokinesis. The cytoplasm divides. Animal cells pinch inward along a contractile actin ring, forming a cleavage furrow; plant cells build a cell plate outward from the center until it meets the existing wall.

Five stages, one continuous process

Mitosis, also called karyokinesis, is nuclear division, and OpenStax divides it into prophase, prometaphase, metaphase, anaphase and telophase. It is worth reading the qualifier that accompanies that list: with the exception of the metaphase to anaphase transition, the phases are not discrete and happen as a continuous process. The stage names are a description of what a cell looks like at a given moment, not a set of switches it flips. Cytokinesis, the physical separation of the cytoplasmic components into two daughter cells, is sometimes counted as the second main part of the mitotic phase and sometimes viewed as a separate process that may or may not follow.

Where students go wrong

Prometaphase is where the trouble usually starts, because a student can meet a four-stage list somewhere and a five-stage list somewhere else. Both OpenStax books used here name five, and so does Cooper on NCBI Bookshelf, which describes prometaphase explicitly as a transition period between prophase and metaphase. Learn the five, and a four-stage list then reads as the same sequence with that transition merged into prophase. The second trap is the vocabulary shift at anaphase: once sister chromatids separate, each one is called a chromosome, so the chromosome count momentarily doubles without any DNA being copied.

Where this leads next

Mitosis is only the short part. Approximately 95 percent of a cell's cycle is spent in interphase, the growth and replication period that precedes it, which is the cell cycle page. Meiosis reuses every one of these stage names with a roman numeral attached, so once this sequence is solid the mitosis and meiosis comparison is mostly about what meiosis I adds rather than a second list to memorize. Cytokinesis is also the point where plant and animal cells visibly diverge, which is the plant cell and animal cell comparison.

Common mistakes

  • Learning four stages and then meeting prometaphase in an exam. OpenStax and Cooper both name five, with prometaphase between prophase and metaphase.
  • Saying chromosomes line up in pairs at the metaphase plate of mitosis. Homologs do not pair in mitosis; that happens in meiosis I.
  • Confusing the cleavage furrow with the cell plate. The furrow pinches an animal cell inward; the plate builds outward from the center of a plant cell.
  • Treating the stages as discrete switches. Apart from the metaphase to anaphase transition, they run continuously into one another.

Related concepts

  • Mitosis vs meiosis: Mitosis is a single nuclear division that produces two nuclei genetically identical to the original and at the same ploidy level.
  • Plant cell vs animal cell: Both are eukaryotic, so both have a plasma membrane, nucleus, ribosomes, mitochondria and the endomembrane system.
  • Cell cycle: The eukaryotic cell cycle has four phases: G₁, S and G₂, which together make up interphase, followed by M phase, the mitotic phase.

Sources