1. The Cell Cycle:

2. Why do cells divide?

3. Reasons for Cell Division 1.Growth and Development (why you aren’t the same height as you were 10 years ago) 2.Repair/Replace damaged cell or cell parts (think of a nasty scrape and how it heals) 3.Limiting Cell Size (cell limited by its protein needs which is regulated by DNA) 4.Reproduction (related to meiosis…more on this next week)

4. BASIC GENETICS Each cell in the human body contains two sets of 23 chromosomes Mitosis identically replicates this information Each cell therefore has the same genetic material

5. When cell is not dividing… ● DNA molecules in extended, uncondensed form = chromatin ● Cell can only use DNA to produce molecules when in extended state. When cell is preparing for division… ● DNA molecules condense to form chromosomes prior to division. – each chromosome is a single molecule of DNA – easier to sort and organize DNA into daughter cells

6. Unreplicated eukaryotic chromosome arm centromere

7. Prior to cell division: chromosomes (DNA) are replicated (duplicated) duplicated chromosome duplicated chromosome – attached at their centromeres – as long as attached, known as Sister Chromatids

8. daughter chromosomes sister chromatids

9. The Cell Cycle: Interphase(comprises 95 % of the cell cycle): G1, S, G2 (M) Phase: Mitosis (prophase, metaphase, anaphase, telophase) So if the whole cell cycle takes 8 hours for this particular cell…then Mitosis would only take 24 minutes.

10. G1: This is where organelle duplication occurs. It also is the checkpoint for the following: CELL SIZE, NUTRIENTS, GROWTH FACTORS and DNA DAMAGE Is called the “restriction point” in animal cells (why do you think this is?) Is much shorter in embryonic and cancer cells In cancer cells can even be nonexistent. (Why do you think this is?)

11. G0: Cells that do not require a lot of replication such as neural tissue remain in this stage for a long time. (Any other types of tissues that you think would remain in this stage? How about types of tissues that replicate fast?)

12. S Phase: The cell is committed to cell division once this process starts DNA and centrosome (remember this structure?) replication occur during this phase Replication of DNA leads to 2 identical sets of daughter chromosomes

13. G2: Cell growth continues Enzymes and proteins are synthesized for cell division DNA damage is checked for. Proper completion of DNA synthesis is required before cell can initiate mitosis (so what happens if DNA is damaged?)

14. Embryonic Cells: Cell growth is not part of the cell cycle All energy is put into DNA synthesis (requires ATP!) G1 does not occur and G2 is very short (If interphase is 95% of the cell cycle then what does this mean about how long it takes for the cell division to occur?) Each round of division subdivides the original cytoplasm into smaller and smaller cells until adult cell size is reached (what do I mean by “adult” cell size?)

15. The Division of Somatic cells (non reproductive cells) in eukaryotic organisms. - A single cell divides into two identical daughter cells - Daughter cells have same # of chromosomes as does parent cell. (M) Phase = Mitosis

16. Mitotic Cell Division 2 major processes: Mitosis – nuclear division => preserves diploid number of chromosomes Cytokinesis – cytoplasmic division => cell divides into two daughter cells

17. Mitosis 4 sub-phases: 1 st – Prophase 2 nd – Metaphase 3 rd – Anaphase 4 th – Telophase and Cytokinesis Secret to remembering phases in order…(IPMAT) DEMOs: http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html#http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter11/animations.html# http://www.cellsalive.com/mitosis.htm

18. Prophase i) chromosomes condense 3 major events ii) spindle fibers form iii) chromosomes are captured by spindle

19. chromatin nucleolus nucleus centrioles condensing chromosomes kinetocore Prophase

20. This is what prophase actually looks like under a microscope

21. Metaphase Sister chromatids align along equator of the cell, with one kinetochore facing each pole centrioles spindle fibers Sister Chromatids

22. Anaphase sister chromatids separate spindle fibers attached to kinetochores shorten and pull chromatids towards the poles. free spindle fibers lengthen and push poles of cell apart

23. Telophase spindle fibers disintegrate nuclear envelopes form around both groups of chromosomes chromosomes revert to their extended state nucleoli reappear cytokinesis occurs, enclosing each daughter nucleus into a separate cell

24. cytokinesis Cytokinesis: the process by which the cytoplasm of the cell divides

25. WHICH PHASE IS WHICH??

26. How is Cell Division Controlled? External regulation: Contact inhibition Internal regulation: Proteins Stop and Go signals

27. EXTERNAL REGULATION Contact Inhibition: Normal cells will reproduce until they come into contact with other cells. When cells come into contact with other cells, they respond by not growing – the proteins on the cell membrane surface signals each other

28. INTERNAL REGULATION Proteins: Specific proteins called cyclins have been found to regulate the cell cycle in eukaryotic cells –The amount of this protein in the cell rises and falls in time with the cell cycle. A sample of cytoplasm is removed from a cell in mitosis. The sample is injected into a second cell in G2 of interphase. As result, the second cell enters mitosis. Cyclins were discovered during a similar experiment to this one

29. INTERNAL REGULATION cont.. Stop and Go signals: If the centromere is not properly attached to spindle microtubules a molecular signal is sent that delays anaphase until they are correctly attached