1. AP Biology: Chapter 12 The Cell Cycle

2. Cell Division Cell division consists of two phases: Nuclear Division (divides material in the nucleus) Cytokinesis (divides the cytoplasm) There are 2 kinds of nuclear division Mitosis (divides the nucleus so that both daughter cells are genetically identical) Meiosis (a reproductive division, producing daughter cells that contain half the genetic material of the parent)

3. First Step to Cell Division The first step in either mitosis or meiosis begins with the condensation of the genetic material (chromatin) into tightly coiled bodies (chromosomes).

4. Chromosomes Each chromosome is made of two identical halves call sister chromatids. Chromatids are connected at the centromere. Chromosomes are tightly coiled DNA. In diploid cells, there are 2 copies of every chromosome. These two copies are called homologues. One homologue originated from the material parent, the other from the paternal parent. Humans have 46 chromosomes, 23 homologous pairs.

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6. Mitosis There are four phases in mitosis Prophase Metaphase Anaphase Telophase (Cytokinesis)

8. The Cell Cycle The cell has a cycle (a “life cycle” sort of)

9. The Cell Cycle Most of the life of a cell is spent in the NON- dividing phase called interphase. The dividing phase of the cell’s life is called the mitotic phase. The cell alternates between interphase and the mitotic phase The cell-cycle is a well-ordered sequence of events. Some cells go through repeated cell cycles Other cells never or rarely divide once they are formed (nerve and muscle cells)

10. Mitotic Phase (M phase) M phase is the shortest part of the cell cycle and the phase during which the cell actually divides. It includes: MITOSIS ---division of the nucleus CYTOKINESIS---division of the cytoplasm

11. Interphase (non-dividing phase) Interphase is the non-dividing phase of the cell. This phase includes most of the cell’s growth and metabolic activities: Is about 90% of the cell cycle Is a period of intense biochemical activity during which the cell grows and copies its chromosomes. There are 3 parts to interphase: 1. G1 PHASE (FIRST GROWTH PHASE) 2. S PHASE (SYTHESIS PHASE, DNA IS SYNTHESIZED AS CHROMOSOMES ARE DUPLICATED) 3. G2 PHASE (SECOND GROWTH PHASE)

12. The Cell Cycle

13. G1, S, and G2 phases G1 of interphase: Generalized cell growth and development S phase: Growth and duplication of DNA G2 of interphase: Well defined nucleus Duplicated chromosomes cannot be seen

14. The Mitotic Cell Cycle ( 10% of cell cycle) Mitosis is a continuous process, but for ease of description, mitosis is usually divided into five stages: PROPHASE METAPHASE/PROMETAPHASE ANAPHASE TELOPHASE (CYTOKINESIS) When cytokinesis occurs, it usually is occuring at the same time as telophase of mitosis

15. Prophase Three activities occur: Nucleoli disappear and chromatin fibers condense into observable chromosomes. Nuclear envelope breaks down. Mitotic spindle Mitotic spindle is assembled (spindle will assist in pulling apart sister chromatids.)

16. Metaphase The chromosomes are distributed across the metaphase plate. Metaphase ends when the microtubules are fully attached to the kinetochores,

17. Mitotic Spindle

18. Figure 12.7 Testing a hypothesis for chromosome migration during anaphase

19. Anaphase Anaphase is characterized by movement! Sister chromotids split fully apart into separate chromosomes and move toward opposite poles of the cell Because kinetochore fibers are attached to the centromeres, the chromosomes move in a “V” shape Simultaneously, the poles of the cell move farther apart, elongating the cell. AP EXAM: remember that the kinetochore fibers are a type of microtubule (cytoskeleton)

20. Telophase and Cytokinesis Nonkinetochore microtubules further elongate the cell Daughter nuclei begin to form at the two poles Nuclear envelopes form around the chromosomes Nucleoli reappear Microfilaments form a ring inside the plasma membrane. They shorten and act as purse strings to “cut” the cell into two cells.

22. By the end of Cytokinesis Mitosis, the equal division of one nucleus into two genetically identical nuclei is complete Cytokinesis has begun and the appearance of two separate daughter cells occurs shortly after mitosis is completed

23. Figure 12.8 Cytokinesis in animal and plant cells

26. Figure 12-09x Mitosis in an onion root

27. Figure 12.9 Mitosis in a plant cell

28. AP Bio LAB 3A - Mitosis Use the Onion Root (Allium) prepared slides Use the Whitefish cells Begin the Lab by looking for the different phases of Mitosis Sketch each stage for both the plant and animal slides **Note: Computer activity - EC – highly recommended

29. Figure 12.10 Bacterial cell division (binary fission) (Layer 1)

30. Figure 12.10 Bacterial cell division (binary fission) (Layer 2)

31. Figure 12.10 Bacterial cell division (binary fission) (Layer 3)

32. Figure 12.15 The effect of a growth factor on cell division

33. Figure 12.15x Fibroblast growth

34. Regulation of the Cell Cycle A molecular control system drives the cell cycle Normal growth, development and maintenance depend on the timing and rate of mitosis. Various cell types differ in their pattern of cell division; for example: HUMAN SKIN CELLS DIVIDE FREQUENTLY LIVER CELLS ONLY DIVIDE IN APPROPRIATE SITUATIONS, SUCH AS WOUND REPAIR NERVE, MUSCLE, AND OTHER SPECIALIZED CELLS DO NOT DIVIDE IN MATURE HUMANS

35. Cell-Cycle Control The cell cycle is coordinated by the cell-cycle control system, a molecular signaling system which cyclically switches on appropriate parts of the cell-cycle machinery and then switches them off The cell-cycle control system consists of a cell- cycle molecular clock and a set of checkpoints that ensure that appropriate conditions have been met before the cycle advances. When the control system malfunctions, cancer may result

37. Particulars about M-Phase If essential nutrients are not available, cells will not divide Growth factors are necessary for growth Crowding inhibits cell division, called Density-Dependent Inhibition Most cells need a substrate to anchor to, called Anchorage-Dependent

38. Cyclin & Cyclin-Dependent Kinases (p240) Kinases that drive cell cycle are actually present at a constant concentration in a growing cell – but most of the time they are INACTIVE. Kinases need to be attached to cyclin to be active --- these are called cyclin-dependent kinases (CDK) inactive with just CDK MPK [kinase] – “maturation promoting factor” OR “M-Phase Promoting factor” –formed with CDK + Cyclin

39. Cyclin and MPF (note p239-240)

40. Cancer Cells Cancer cells have escaped the cell-cycle controls Cancer cells do not respond normally to the body’s control mechanisms (checkpoints) They divide excessively, invade other tissues and, if unchecked can kill the whole organism

44. Normal Breast Tissue:

45. Malignant Breast Tissue:

46. Cancer Cells (video to view) Cancer cells do not stop growing in response to cell density Cancer cells do not stop dividing when growth factors are depleted Cancer cells may make their own growth factors Cancer cells may have an abnormal growth factor signaling system Cancer cells in culture are immortal in that they continue to divide indefinitely

47. Cancer Cells If the cells remain at the original site, the mass can be completely removed by surgery A tumor is defined as “malignant” according to an examination of the mitotic cells in the tumor and potential of the cells invading other tissue. A malignant tumor is invasive enough to impair normal function of one or more organs of the body. Only an individual with a malignant tumor is said to have cancer