BRAINCAKEProphase
Prophase is the first stage of mitosis. It follows G2 of interphase, so the DNA has already been replicated.
The main events of prophase are:
• Chromosomes condense. The chromatin coils up tightly, so the chromosomes become shorter and thicker and can be seen with a light microscope. Each chromosome is now visible as two sister chromatids joined at the centromere.
• The nucleolus disappears.
• The spindle forms. In animal cells, the two centrioles (which were replicated during interphase) move to opposite poles of the cell. Protein microtubules grow out from them to form the spindle fibres. Plant cells have no centrioles, but still form a spindle from microtubule-organising regions.
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Key terms in this lesson
- sister chromatids
- The two identical copies of a chromosome, joined at the centromere, produced when DNA replicates before cell division.
- spindle fibres
- Protein microtubules that form a spindle-shaped structure during cell division and attach to chromosomes to separate them.
More in The Cell Cycle
All 18 lessons in The Cell Cycle · All Edexcel AS-level Biology topics