1. CELL DIVISION

2. GUIDE: CELL CYCLEMITOSISMEIOSIS

3. Cell Cycle Describes the behavior of the cell as they grow and divide Integrates a growth phase and a divisional phase The Cycle has 4 steps

4. Cell Cycle The passage of a cell through the cell cycle is controlled by proteins in the cytoplasm. – Among the main players in animal cells are: Cyclins – G 1 cyclins (D cyclins) – S-phase cyclins (cyclins E and A) – mitotic cyclins (B cyclins) Their levels in the cell rise and fall with the stages of the cell cycle.

5. Cell Cycle Cyclin-dependent kinases (Cdks)kinases – a G 1 Cdk (Cdk4) – an S-phase Cdk (Cdk2) – an M-phase Cdk (Cdk1) Their levels in the cell remain fairly stable, but each must bind the appropriate cyclin (whose levels fluctuate) in order to be activated. They add phosphate groups to a variety of protein substrates that control processes in the cell cycle.phosphate groups

6. INTERPHASE The largest part of the cycle, in most cells is interphase. The time spent between divisions. Produces all materials required for growth. Preparation for division. It has 3 parts; G1, S, G2

7. INTERPHASE G1 phase Growth of the cell, at the beginning of this phase, cell is the smallest it will ever be. Metabolic changes prepare the cell for division. At a certain point - the restriction point - the cell is committed to division and moves into the S phase.

8. INTERPHASE S phase DNA synthesis replicates the genetic material. Each chromosome now consists of two sister chromatids.

9. INTERPHASE G2 phase Metabolic changes assemble the cytoplasmic materials necessary for mitosis and cytokinesis. Cell enters the second growth phase. The cell grows and makes preparations for Mitosis. 1. Organelles duplication 2. DNA begins to condense from chromatin to chromosomes 3. Microtubules begin to form.

10. INTERPHASE

11. M phase A nuclear division (mitosis) followed by a cell division (cytokinesis).

12. MITOSIS 4 Phases PROPHASE METAPHASE ANAPHASE TELOPHASE

13. PROPHASE: The Cell begins the division process 1.The nucleolus disappears, 2.The nuclear membrane breaks apart

14. PROPHASE Prophase occupies over half of mitosis. The nuclear membrane breaks down to form a number of small vesicles and the nucleolus disintegrates. A structure known as the centrosome duplicates itself to form two daughter centrosomes that migrate to opposite ends of the cell

15. PROPHASE The centrosomes organize the production of microtubules that form the spindle fibers that constitute the mitotic spindle. The chromosomes condense into compact structures. Each replicated chromosome can now be seen to consist of two identical chromatids (or sister chromatids) held together by a structure known as the centromere.

16. PROPHASE

17. Metaphase The Second Phase of Mitosis The Nuclear Membrane is completely gone

18. METAPHASE The chromosomes, led by their centromeres, migrate to the equatorial plane in the midline of cell - at right-angles to the axis formed by the centrosomes. – This region of the mitotic spindle is known as the metaphase plate.

19. METAPHASE The spindle fibers bind to a structure associated with the centromere of each chromosome called a kinetochore. Individual spindle fibers bind to a kinetochore structure on each side of the centromere. The chromosomes continue to condense. The chromosomes align themselves along the metaphase plate of the spindle apparatus.

20. ANAPHASE The third phase of Mitosis The shortest stage of mitosis Diploid sets of daughter chromosomes separate They are pushed and pulled toward opposite poles of the cell by the spindle fibers The separated sister chromatids are now referred to as daughter chromosomes.

21. TELOPHASE The nuclear membrane and nucleoli (nucleus) reform. The nuclear membrane reforms around the chromosomes grouped at either pole of the cell, the chromosomes uncoil and become diffuse, and the spindle fibers disappear. Cytokinesis is nearly complete

22. TELOPHASE The Cell Plate begins to form (Plants) In animals there is a constriction of the cytoplasm. The Cell prepares for finial division

23. CYTOKINESIS The final stage of Mitosis The cytoplasm, organelles, and nuclear material are evenly split and two new cells are formed.

24. CYTOKINESIS

25. DAUGHTER CELLS The two new cells – each exactly like the other – are called Daughter Cells

26. Why do Cells Divide? The larger a cell becomes, the more demands the cell places on it's DNA. It also has more trouble moving enough food and wastes across its cell membrane.

27. Why do Cells Divide? The bigger the cell gets the harder it becomes to move food and waste across the membrane This happens because the surface area and volume ratio does not stay the same as the cell size increases.

28. Why do Cells Divide? How much food and other material is required, and how much waste the cell produces and has to get rid of, is related to the volume of the cell. (inside)

29. Why do Cells Divide? As a cell gets bigger there comes a time when its surface area is not large enough to meet the demands of the cell's volume and the cell stops growing.

30. Why do Cells Divide? So, once cells reach a certain size they must divide in order to continue to function – or they will no longer be able to take in nutrients and eliminate waste.

31. MEIOSES Takes place in the Gametes of an organism People have a Chromosome count of 46 When an egg joins a sperm the count must stay at 46 to remain human So, the egg can only have 23 chromosomes, and the sperm can only have 23 chromosomes But, the integrity of the organism must be maintained.

32. MEIOSES During Meiosis gamete (sex) cells undergo a “double division”, maintaining the DNA, but reducing the chromosomal count to 23

33. MEIOSIS - Two Parts MEIOSES 1 MEIOSES 2

34. MEIOSES 1: Prophase 1: Chromosomes become more visible, contain 2 chromatids. Maternal and Paternal Chromosomes are side by side.

35. MEIOSES 1 Metaphase 1: Centromeres of each chromosome have spindle microtubules attached. Bivalents line up randomly along the equator (Random Orientation) Crossing over, exchange of DNA are terminated.

36. MEIOSES 1 Anaphase 1: Homologous chromosomes seperate and are pulled to opposite poles by spindle microtubules. Result: There is independent assortment of genes, not linked.

37. MEIOSES 1 Telophase 1: The chromosome are surrounded by two new membranes (optional).

38. MEIOSE 2

39. At the end of Meiosis the individual Gamete cell has divided from one cell to four. Males produce 4 viable sperm. Females produce 1 viable egg and 3 non functioning polar bodies. Results

40. Meiosis ensures that all living organisms will maintain both Genetic Diversity and Genetic Integrity MEIOSIS