1. Cell Division and Mitosis Ch. 5

2. God’s Command to Nature Genesis God created all living things and gave them a command: “Be fruitful and multiply, fill the earth and subdue it…”

3. Cell Division There are FOUR main functions of Cell Division: 1. In unicellular organisms, cell division is the way these organisms reproduce.  The cell DIVIDES producing a duplicate or copy of itself

4. Cell Division In multicellular organisms, cell division has several functions: 2. Regeneration- occurs when parts or organisms that have been damaged grow back or are replaced.  Ex. A starfish can grow a new arm if one is cut off.  Do you know of any other animals that can replace lost parts?

5. Cell Division 3. Healing- another function of cell division is the healing of wounds.  Whenever you have a cut or scrape on your skin, you can see the healing take place over a period of time.  While the wound heals, new cells are made through cell division to replace the destroyed and damaged cells.

6. Cell Division 4. A fourth important result of cell division is the growing process.  After a cell divides, both new cells grow and divide to form more new cells  Some cells can divide every few hours

7. Prokaryotic Cell Division Bacterial cells reproduce by B BB Binary Fission BBegins with DNA replication; each copy moves to opposite sides of cell FFollowed by elongation of cell, and formation of a septum (separation) between the two halves, forming two new cells RResults in two cells that are identical (clones) of original cells

8. Binary Fission

9. Eukaryotic Cell Division Two forms  Mitosis grow, replace dead or worn out cells, or to repair wounds Asexual reproduction in fungi, protists, some plants/animals  Meiosis Formation of gametes for sexual reproduction

10. The Cell Cycle The length of time the cell cycle takes depends on the type of cell. Usually the more specialized the cell the less likely it is to divide.

11. Ever wondered how often your cells regenerate? Intestinal lining 2 to 30 days Skin 21 to 30 days Red blood cells 90 to 120 days The pancreas 5 to 12 months Muscles 6 months to 3 years Tissues 1 to 7 years Bones 8 months to 4 years

12. G1 S G2 Mitosis telophase anaphase metaphase prophase interphase Cell Cycle

13. The Cell Cycle: Interphase When a cell is not dividing it is said to be in Interphase: G1: Gap 1, cells are recovering from an earlier cell division, synthesizing organelles and growing S: Synthesis, DNA replication occurs G2: Gap, cells are making sure all the DNA was replicated correctly; a little more growth; the chromosomes start to undergo condensation, becoming tightly coiled; Centrioles (microtubule-organizing centers) replicate and one centriole moves to each pole.

14. Interphase interphaseinterphase

15. DNA and Cell Division (Interphase) DNA During cell division, the genetic material DNA, needs to be copied and divided between the two new cells chromosomes DNA in cells is divided into long chains called chromosomes (“volumes” of DNA) histones Chromosome DNA is wrapped around proteins called histones to organize it

16. Eukaryotic Chromosome Structure chromatin Normally, chromosomes are spread out in a form called chromatin chromosomes During mitosis, chromatin folds up and condense to become chromosomes

17. Eukaryotic Chromosomes Chromosomes must be replicated before cell division.  sister chromatids  sister chromatids: are 2 copies of the chromosome centromere  The sister chromatids are bound together in the middle at a centromere

19. Maintaining Chromosome Number mitosis, cytoplasmic division chromosome (unduplicated) in daughter cell at interphase chromosome (unduplicated) in daughter cell at interphase chromosome (unduplicated) in cell at interphase same chromosome (duplicated) in interphase prior to mitosis

20. The Cell Cycle: Cell Division Mitosis (M Phase)  Nuclear Division Cytokinesis (C phase)  Cytoplasmic Division

21. G0G0 The Cell Cycle

22. Mitosis Nuclear Division Dividing up the genetic material (DNA)

23. Mitosis Mitosis is divided into 4 phases: 1. Prophase 2. Metaphase 3. Anaphase 4. Telophase

24. Mitosis 1. Prophase:  chromosomes condense and appear as sister chromatids joined at centromere  cytoskeleton disassembles  centrioles move to each pole of the cell; spindle apparatus is assembled  nuclear envelope dissolves

25. The Spindle Apparatus Consists of two distinct sets of microtubules  Each set extends from one of the cell poles  Two sets overlap at spindle equator Moves chromosomes during mitosis centrosomes centrioles In both plant and animal cells, spindle fibers originate from centrosomes; in animal cells, centrosomes are called centrioles

26. one spindle pole one of the condensed chromosomes spindle equator microtubules organized as a spindle apparatus one spindle pole Spindle Apparatus

27. Prophase

28. Mitosis 2. Metaphase: -spindle fibers pull the chromosomes to align them at the center of the cell (in the “middle” of the cell) called the metaphase plate

29. Metaphase

30. Mitosis 3. Anaphase: - microtubules pull sister chromatids away toward the poles

31. Anaphase

32. Mitosis 4. Telophase: -spindle apparatus disassembles -nuclear envelope forms around each set of sister chromatids -chromosomes begin to uncoil -nucleolus reappears in each new nucleus

33. Telophase

34. Cytokinesis Division of the cytoplasm Usually occurs between late anaphase and end of telophase Two mechanisms  Cell plate formation (plants)  Cleavage furrow (animals)

35. Cytokinesis: Animal Cell Cleavage furrow – is the pinching in of the cell membrane to divide the cell into 2 new cells

36. Cleavage Furrow

37. Cell Plate Formation  In plant cells, a cell plate will form between the two dividing nuclei to form the new cell wall Cytokinesis: Plant Cells

39. Mitosis/Cytokinesis outcome 1 parent cell  2 identical daughter cells Chromosome number remains the same from one generation to the next

40. Mitosis: plant vs. animal cells Plant cellAnimal Cell CentriolesAbsentPresent Cytokinesis Cell plate formation Cleavage furrow

41. Control of the Cell Cycle The cell cycle is controlled at three checkpoints: 1. G 1 /S checkpoint -the cell “decides” to divide 2. G 2 /M checkpoint -the cell makes a commitment to mitosis 3. late metaphase (spindle) checkpoint -the cell ensures that all chromosomes are attached to the spindle

43. Control of the Cell Cycle cyclins – proteins produced in synchrony with the cell cycle -regulate passage of the cell through cell cycle checkpoints cyclin-dependent kinases (Cdks) – enzymes that drive the cell cycle -activated only when bound by a cyclin

44. Control of the Cell Cycle Proto-oncogenes: -some encode receptors for growth factors -some encode signal transduction proteins -become oncogenes when mutated -oncogenes can cause cancer when they are introduced into a cell