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Prophase

Prophase: The nuclear envelope breaks down and the nucleolus disappears.Chromosomes shorten and thicken and become visible. Each chromosome consists of two identical chromatids held together at the centromere.The centrioles move to opposite poles of the cell and spindle fibres grow from each centriole towards the middle of the cell.Plant cells develop spindles but do not have centrioles. The chromosomes start to move towards the middle of the cell.

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Specification: AQA Biology (7401), AS-level, 3.2.2 All cells arise from other cells. Topic: The Cell Cycle.

Key terms in this lesson

nucleolus
A dense structure within the nucleus where ribosomal RNA is made and ribosomes are assembled.
centromere
The region of a chromosome where the two sister chromatids are held together and where spindle fibres attach.
chromatid
One of two identical copies of a chromosome, joined at the centromere, formed by DNA replication.
spindle fibres
Protein fibres that extend across a dividing cell and attach to the centromeres of chromosomes, pulling them apart.

More in The Cell Cycle

All 12 lessons in The Cell Cycle · All AQA AS-level Biology topics