1. The division of the nucleus
Mitosis
The division of the nucleus
© 2016 Paul Billiet ODWS

2. Conception All animals begin as a fertilised egg cell (a zygote)
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3. Then it divides… © 2016 Paul Billiet ODWS
© 2016 Paul Billiet ODWS

4. … and divides © 2016 Paul Billiet ODWS
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5. Until it becomes an embryo
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6. But what actually happens when a cell divides?
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7. Interphase (plant cell)
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8. Interphase: In between cell divisions
Centriole
Cytoplasm
Nucleus
Plasma membrane
Nucleus envelope
Nucleolus
The working cell
It grows in size (protein synthesis)
It copies its genetic material (replication)
© 2016 Paul Billiet ODWS

9. Prophase
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10. Prophase: Division begins
Centriole divides
Threads appear in the nucleus =
Chromosomes condensing
Nucleus swells
Nucleolus disappears
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11. End of prophase: The nucleus disappears
Nucleus envelope breaks down
Spindle fibres grow out from the ends of the cell
Centromere
Sister chromatids
Chromosomes appear as two threads (the chromatids) joined by a constriction (the centromere)
© 2016 Paul Billiet ODWS

12. Metaphase
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13. Metaphase: The chromosomes are organised
Chromosomes line up across the equator of the spindle
Joined to fibres by their centromeres
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14. Anaphase
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15. Anaphase: The chromosomes split
The sister chromatids of each chromosome split
The spindle pulls one to each pole
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16. Telophase
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17. Telophase: The end of mitosis
The nuclei reform
Each one contains a complete set of chromosomes
A new nuclear envelop forms
The chromosomes uncoil
The cytoplasm divides in two to form two identical daughter cells
The cells goes back to work
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18. Cytokinesis
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19. Using confocal microscopy
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20. Interphase
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21. Prophase
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22. Metaphase
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23. Anaphase
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24. Telophase
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25. Cytokinesis
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26. Plant v Animal cells Centriole Cytokinesis: Cell plate v cleavage
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27. Chromosomes and cell division
Multicellular organisms copy their chromosomes before cell division
The cells must grow to a mature size
Interphase
The nucleus divides, distributing the chromosomes into two equal groups
Mitosis
The cytoplasm then divides each part taking a nucleus
Cytokinesis
© 2016 Paul Billiet ODWS

28. Cytokinesis division of the cytoplasm
The cell cycle
Some cells may stay in this stage for over a year
Cytokinesis division of the cytoplasm G0 M
Mitosis G2
First growth phase.
Varies in length G1
INTERPHASE
Second growth period
Copying of chromosomes S
G1 + S + G2 = INTERPHASE
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29. Cell cycles are not uniform
Cell type
Cell cycle / h
Bean root tip
19.3
Mouse fibroblast 22
Chinese hamster fibroblast 11
Mouse small intestine epithelium 17
Mouse oesophagus epithelium
181
© 2016 Paul Billiet ODWS

30. Cyclins help control cell division
Cyclins are proteins
Cyclins are expressed during different stages of the cell cycle
Interact with cyclin dependent kinases (CDK)
CDKs phosphorylate other molecules
The phosphorylated molecules bring about changes in the activity of the cell
Cyclins rise and fall at critical points in the cell cycle
© 2016 Paul Billiet ODWS

31. Cyclins and the cell cycle
© 2016 Paul Billiet ODWS

32. Cancer Mutation of regulatory genes (oncogenes)
Uncontrolled cell division primary tumour
Metastasis secondary tumour.

33. eg retinoblastoma protein Chromatin modifying enzymes
Cancer and cyclins
MUTOGENS
G1  S
Cyclins synthesized
CDK activated
Regulatory proteins phosphorylated
eg retinoblastoma protein
Chromatin modifying enzymes
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34. Cancer cells v normal cells
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