Mitosis and cytokinesis are two steps
- The idea
- Predict
- See it
- Why
- Check
The idea
“When the nucleus divides, the cell divides with it, in one event.”
Most diagrams draw the nucleus splitting and the cell pinching in two in one picture. The steps usually overlap too, so they look like one event.
The short version
The mistake: When the nucleus divides, the cell divides with it, in one event.
What's actually true: Mitosis divides the nucleus and cytokinesis divides the cytoplasm. A cell can finish mitosis without splitting.
- Mitosis divides the nucleus. Sister chromatids are pulled to opposite ends, and a nuclear envelope forms at each end. That gives two nuclei with identical DNA.
- Cytokinesis divides the cytoplasm. Animal cells pinch in at a cleavage furrow, using a ring of actin and myosin. Plant cells build a cell plate from vesicles.
- The steps usually overlap but use different machinery, so mitosis can finish even when cytokinesis is blocked or skipped.
- Two nuclei in one cell usually means mitosis ran without cytokinesis.
On the exam: Mitosis splits the nucleus. Cytokinesis splits the cell. Count nuclei and cells separately.