1. Structure, function and growth of prokaryote and eukaryote cells (ii) Cell growth and Cell cycle Interphase Mitosis Mitotic index Control of the cell cycle Abnormal Cell division: cancer cells

2. Cell Cycle When cells reach a certain size they must stop growing or divide. The cell cycle is the period from the formation of a new cell until that cell divides itself The length of the cycle depends on the cell – but is usually 8 – 20 hours

3. The Cell Cycle CK

4. Interphase… G 1 (First Gap Period)  Cell grows and increases in mass Cell membrane (+ wall) are increased Number of organelles increase Chemical preparation for DNA Synthesis (enzymes, deoxyribose sugars, nucleotide bases and phosphates synthesised)

5. Interphase S phase (synthesis)  Replication of DNA Chromosomes held together by centromere  In animals centriole pairs duplicate

6. Interphase G 2 (Second gap phase)  Cell builds up energy reserves  Increased protein synthesis

7. Mitosis Revision – complete the mitosis diagram (note this is from standard grade)

8. Mitosis Compare this to your SG diagram. Name the stages  Interphase  Prophase  Metaphase  Telophase  Cytokinesis What features characterise each stage?

9. Mitosis Prophase  Chromosomes condense (coil and fold up) to become visible. Joins onto spindle fibre Chromatids in condensed form

10. Mitosis – prophase cont…  Cytoskeleton disintegrates (its components (microtubules) are used to begin spindle formation)  Spindle formation begins between centrosomes (aka Microtubule organising centres – MTOCs)  Nuclear Membrane starts to break up

11. Mitosis – prophase cont…

12. Mitosis Metaphase  Spindle continues to grow from centrosomes (which are now at the poles)  Chromosomes line up across the centre of the cell

13. Mitosis – metaphase cont..  Chromosomes attach to the spindle fibre by the kinetochore in the centromere  The arrangement of the chromosomes across the equator is also known as the metaphase plate.

14. Mitosis – metaphase cont…

15. Mitosis Anaphase  Centromeres divide  Sister chromatids separate and the chromosomes are pulled to the poles

16. Mitosis – anaphase cont…

17. Mitosis Telophase  Chromosomes begin to de-condense  Nuclear membrane reforms  Spindle disassembles and reassembles as the cytoskeleton in the 2 new cells

18. Mitosis – telophase cont…

19. Cytokinesis Dividing of the cytoplasm and organelles Animals  Cytoplasm is pinched by a ring of contractile microfilaments (made up of the proteins actin and myosin)  As the ring gets smaller it forms a cleavage furrow

20. Cytokinesis cont…

21. In plants  Membrane vesicles spread across the equator of the cell.  They merge to form plasma membrane  The new membranes lay down the cell wall between the two cells.

22. Cytokinesis cont…

23. Mitotic Index The fraction (or percentage) in a microscope field that contain condensed chromosomes (i.e. Undergoing mitosis)

24. Learning Activities Look at web animations  www.biozone.co.uk/links.html www.biozone.co.uk/links.html Cell biology – Mitosis / Meiosis – How cells divide Posters Card sort (pictures / names / descriptions) Read Dart pg 9-14 and take notes Use Scholar Advanced Higher Questions