3.7. Mitosis

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Mitosis is the process of cell division. After the DNA has been replicated in the S phase of the cell cycle, the cell enters mitosis.

  • One cell → two cells
  • o → 0 → 8 → oo 😉

After the DNA has been replicated, the cell enters mitosis.After the DNA has been replicated, the cell enters mitosis.

Chromosomes, mitotic chromosomes, and sister chromatids

These concepts are easily confused:

Concept Explanation
  • Chromosome
  • One DNA molecule
  • Contains a single set of genes
  • Mitotic chromosome (metaphase chromosome)
  • Two identical DNA molecules
  • Contains a double set of genes
  • Only present during mitosis.
  • Sister chromatids
  • The two main parts of a mitotic chromosomes
  • Separated from each other during the anaphase stage.
  • One sister chromatid contains one DNA molecule = 1 chromosome

Don't confuse chromosomes, mitotic chromosome (metaphase chromosomes), and sister chromatids!Don't confuse chromosomes, mitotic chromosome (metaphase chromosomes), and sister chromatids!

Interphase – S phase

  • The DNA is copied (replicated).
  • The centrosome is replicated.
The DNA and the centrosome are copied during the S-phase in the interphase.The DNA and the centrosome are copied during the S-phase in the interphase. Mitotic chromosomes become visible during prophase.Mitotic chromosomes become visible during prophase.

Prophase

  • The chromatin starts to condense (pack).
  • Mitotic chromosomes are formed.
  • Nuclear membrane dissolves.
  • Centrosomes start to move away from each other.

Structure of the (mitotic) chromosome

The DNA is wound two times around histones, and packed tightly into mitotic chromosomes.

The chromatin is very densely packed in mitotic chromosomes.The chromatin is very densely packed in mitotic chromosomes.

Metaphase

Nuclear membrane completely dissolved.

Mitotic chromosomes tightly packed, in the equatorial plane = metaphase plate.

  • Complete mitotic spindle formed.
Metaphase.Metaphase. Anaphase.Anaphase.

Anaphase

Sister chromatids are pulled towards each pole.

Telophase & cytokinesis

New nuclear membrane starts to form.

Chromosomes are unpacked again, relaxed chromatin forms.

Two new cells form ⇒ cytokinesis.

Telophase.Telophase. Cytokinesis.Cytokinesis.