cell cycle and mitosis

  • cells undergo cell division for:

Growth

repair of damaged tissue

Proliferation of white blood cells ( rapid mitosis so wbc can produce lots of antibodies

Asexual reproduction (fungi, plants mainly)

  • Produces 2 genetically identical daughter cells

Stages of cell cycle:

  • Interphase - cell grows, makes copies of all its DNA and organelles. Would observe chromatin within the nucleus (not condensed into chromosomes)

Stages of interphase:

1. G1 - cell growth, organelle synthesis, protein synthesis

2. S - dna replication

3. G2 - cell growth, organelle synthesis, protein synthesis

Checkpoints for interphase:

G1 checkpoint - checks cell size, has all required proteins and organelles and dna damage. (If this check fails, cell will delay s stage or bail from cell cycle all together. The cell will enter the G0 which prevents the mutated cell from dividing and causing damage in the body.

G2 checkpoint - checks dna replication

  • Mitosis - nucleus divides in 2. By the end the 2 nuclei are genetically identical as they contain the same dna.

Stages of mitosis:

1. Prophase

- chromatin condenses into chromosomes. These are made up of sister chromatids joined toegther at the centromere.

- nuclear envelope breaks down and centrioles move to opposite poles of the cell and start creating spindle fibres.

2. Metaphase

- spindle fibres reach across to the middle of the cell attaching to the centromere of the chromosomes.

- chromosomes are moved by spindle fibres to the equator of the cell to form a plane - metaphase plate - and held in position.

3. Anaphase

- spindle fibres pull sister chromatids apart, pulled to opposite poles of the cell. (Look like little v shapes)

4. Telophase

- chromatids reach the poles, now called chromosomes where nuclear envelope reforms around them

- chromosomes uncoil and decondense back into chromatin and nucleolus forms.

  • cytokinesis - the division of the cell into the 2 separate cells.

Animal cells - cell membrane pinches inwards by the cytoskeleton, forming 2 cells

Plant cells - vesicles form in the centre of the cell which fuse together and with the cell surface membrane, forming 2 cells.