Cell Replication What is the purpose? What is mitosis? 1

Why do cells need to replicate? Nucleus to cytoplasm ratio – as sell matures this ratio gets larger i.e. nucleus gets smaller compared to size of cell. Growth – needed for multicellular organisms to increase in size Development – the ability of undifferentiated cells to become specialised. Maintenance and repair – replacement of those cells that have been damaged or lost.

Cell division INTERPHASECYTOKINESISMITOSIS

Stages of cell replication Interphase ◦ Organelles and DNA copied but NOT visible yet Mitosis ◦ Chromosomes separated into 2 identical nuclei but cell not divided yet Cytokinesis ◦ 2 daughter cells become independent ◦ Cleavage furrow (animal) ◦ Cell plate formation (plants) 4

5 NUCLEUS Homologous Chromosomes Sister chromatids This cell has a : Diploid number = 4 Haploid number = 2 DNA is copied – still in long threads – chromosomes NOT yet completely visible Interphase

6 CENTRIOLE Nuclear membrane breaks down Chromosomes condense so you can now see them Centrioles send out spindle fibres START MITOSIS - Prophase

7 CENTRIOLE Centromeres and spindle fibres drive the chromosomes to the equator Metaphase – line up on equator

8 CENTRIOLE Spindle fibres pull chromatids to opposite poles of the cell. Anaphase

9 Centrioles break down Nuclear membrane forms around each set of chromosomes CENTRIOLE Telophase

Two daughter cells with exactly the same chromosomes as the original parent cell. Cytokinesis 10

Plant Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

Animal Mitosis -- Review Interphase Prophase Metaphase Anaphase Telophase Cytokinesis

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Division of the molecules and organelles of the cytoplasm Separation of new nuclei, to form two new identical daughter cells How do cells replicate? – Cytokinesis Plant New plasma membrane and cell wall are deposited in the centre of the cell Animal Plasma membrane moves inward, pinching the daughter cells apart