1. Mitosis The division of the nucleus © 2010 Paul Billiet ODWSODWS

2. Conception All animals begin as a fertilised egg cell (a zygote) Image Credit: ZygoteZygote

3. Then it divides… Image Credit: www.ehd.org/www.ehd.org/

4. … and divides Released into the Public Domain by JrockleyJrockley

5. Until it becomes an embryo Image Credit: www.scienceclarified.comwww.scienceclarified.com

6. But what actually happens when a cell divides? http://video.google.com/videoplay?docid=- 5522357274832025243&q=mitosis&total=36 8&start=0&num=10&so=0&type=search&plin dex=2 http://video.google.com/videoplay?docid=- 5522357274832025243&q=mitosis&total=36 8&start=0&num=10&so=0&type=search&plin dex=2 http://www.johnkyrk.com/mitosis.html http://www.bio.unc.edu/faculty/salmon/lab/mit osis/mitosismovies.html http://www.bio.unc.edu/faculty/salmon/lab/mit osis/mitosismovies.html

7. Image Credit: www.bioweb.uncc.edu/

8. Interphase: In between cell divisions The working cell It grows in size (protein synthesis) It copies it’s genetic material (replication) Nucleus Nucleus envelope Centriole Nucleolus Cytoplasm Plasma membrane © 2010 Paul Billiet ODWSODWS

9. Image Credit: www.bioweb.uncc.edu/

10. Prophase: Division begins Centriole divides Treads appear in the nucleus = Chromosomes condensing Nucleus swells Nucleolus disappears © 2010 Paul Billiet ODWSODWS

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) © 2010 Paul Billiet ODWSODWS

12. Image Credit: www.bioweb.uncc.edu/

13. Metaphase: The chromosomes are organised Chromosomes line up across the equator of the spindle Joined to fibres by their centromeres © 2010 Paul Billiet ODWSODWS

14. Image Credit: www.bioweb.uncc.edu/

15. Anaphase: The chromosomes split The sister chromatids of each chromosome split The spindle pulls one to each pole © 2010 Paul Billiet ODWSODWS

16. Image Credit: www.bioweb.uncc.edu/

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 © 2010 Paul Billiet ODWSODWS

18. Chromosomes and cell division Multicellular organisms copy their chromosomes before cell division They must grow to a mature size The nucleus divides, distributing the chromosomes into two equal groups Interphase The cytoplasm then divides each part taking a nucleus Mitosis Cytokinesis © 2010 Paul Billiet ODWSODWS

19. The cell cycle G 1 + S + G 2 = INTERPHASE First growth phase. Varies in length Copying of chromosomes Some cells may stay in this stage for over a year Second growth period M G1G1 S G2G2 G0G0 Cytokinesis division of the cytoplasm © 2010 Paul Billiet ODWSODWS

20. Cell cycles are not uniform Cell typeCell cycle / h Bean root tip19.3 Mouse fibroblast22 Chinese hamster fibroblast11 Mouse small intestine epithelium17 Mouse oesophagus epithelium181 © 2010 Paul Billiet ODWSODWS