1. AP Bio Exam Review: Unit 5 – Cell Division

2. Cell Cycle: life of a cell from its formation until it divides
Functions of Cell Division: Reproduction, Growth and Tissue Renewal

3. Genome = all of a cell’s genetic info (DNA)
Prokaryote: single, circular chromosome
Eukaryote: more than one linear chromosomes
Eg. Human:46 chromosomes, mouse: 40, fruit fly: 8

4. Each chromosome must be duplicated before cell division
Duplicated chromosome = 2 sister chromatids attached by a centromere

5. Somatic Cells Gametes Body cells
diploid (2n): 2 of each type of chromosome
Divide by mitosis
Humans: 2n = 46
Sex cells (sperm/egg)
Haploid (n): 1 of each type of chromosome
Divide by meiosis
Humans: n = 23

6. Phases of the Cell Cycle

7. Phases of the Cell Cycle
The mitotic phase alternates with interphase:
G1  S  G2  mitosis  cytokinesis
Interphase (90% of cell cycle)
G1 Phase: cell grows and carries out normal functions
S Phase: duplicates chromosomes
G2 Phase: prepares for cell division
M Phase (mitotic)
Mitosis: nucleus divides
Cytokinesis: cytoplasm divides

8. Mitosis: Prophase  Prometaphase  Metaphase  Anaphase  Telophase

9. Mitosis – nuclear division
1. Prophase
Chromatin fibers condense and coil
Nucleoli disappear
Spindle (microtubules) begins to form
Centrosomes begin to move to opposite ends
2. Prometaphase
Nuclear envelope fragments
Microtubules invade nucleus
Kinetochores attach to microtubules

10. Prophase & Prometaphase

11. 3. Metaphase
Chromosomes line up on metaphase plate at equator
Centrioles are at opposite poles (ends)
4. Anaphase (shortest phase)
Chromatids separate and pulled apart by motor proteins toward opposite ends of cell
Chromatids are called chromosomes now
Cell elongates

12. Metaphase & Anaphase

13. Mitotic spindle at metaphase
Kinetochore = proteins associated with DNA at centromere

14. During anaphase Chromosomes walked to poles by motor proteins
Kinetochore microtubules shorten at ends

15. 5. Telophase
Nuclear membrane re-forms around chromosomes
Chromosomes less condensed

16. Cytokinesis Cytoplasm of cell divided Animal Cells: cleavage furrow Plant Cells: cell plate forms

17. Identify the stages of cell division
I = Interphase – G1
II = Interphase – S phase
III = Interphase – G2
IV = Mitosis
V = Cytokinesis

18. Bacterial cells divide by Binary Fission

19. Cell Cycle Control System
Checkpoint = control point where stop/go signals regulate the cell cycle

20. Major Checkpoints G1 checkpoint (Most important!)
“Go”  completes whole cell cycle
“Stop”  cell enters nondividing state (G0 Phase)
Nerve, muscle cells stay at G0; liver cells called back from G0
G2 checkpoint
M Phase checkpoint
Anaphase does not begin unless chromatids are properly attached to spindle at metaphase plate

21. G1 Checkpoint

22. Internal Regulatory Molecules
Molecules that maintain cell division
Kinases (cyclin-dependent kinase, Cdk): protein enzyme controls cell cycle; active when connected to cyclin
Cyclins: proteins which attach to kinases (Cdk) to activate them; levels fluctuate in the cell cycle
3. MPF: mature-promoting factor; specific Cdk which allows cells to pass G2 and go to M phase

23. External Regulatory Factors
Growth Factor: proteins released by other cells to stimulate cell division
Density-Dependent Inhibition: crowded cells normally stop dividing; cell-surface protein binds to adjoining cell to inhibit growth
Anchorage Dependence: cells must be attached to another cell or ECM to divide

24. Cancer Cells
Cancer: disorder in which cells lose the ability to control growth by not responding to regulation.
multistep process of about 5-7 genetic changes (for a human) for a cell to transform
loses anchorage dependency and density-dependency regulation
Normal Cells
Cancer Cells

25. Tumors = mass of abnormal cells
Benign tumor: lump of cells remain at original site
Malignant tumor: invasive - impairs functions of 1+ organs (called cancer)
Metastasis: cells separate from tumor and travel to other parts of body

26. Types of Reproduction ASEXUAL Produces clones (genetically identical)
Single parent
Little variation in population - only through mutations
Fast and energy efficient
Eg. budding, binary fission
SEXUAL
Meiosis produces gametes (sex cells)
2 parents: male/female
Lots of variation/diversity
Slower and energy consumptive
Eg. humans, trees

27. Chromosomes Somatic (body) cell: 2n = 46 chromosomes
Each pair of homologous chromosomes includes 1 chromosome from each parent
Autosomes: 22 pairs of chromosomes that do not determine sex
Sex chromosomes: X and Y
Females: XX
Males: XY
Gametes (n=23): 22 autosomes + 1 sex chromosome
Egg: 22 + X
Sperm: 22 + X **or** 22 + Y

28. Homologous Chromosomes in a Somatic Cell

29. Karyotype: a picture of an organism’s complete set of chromosomes
Arranged from largest  smallest pair

30. Nondisjunction: chromosomes fail to separate properly in Meiosis I or Meiosis II

31. Non-disjunction disorders

32. Zygote divides by mitosis to make multicellular diploid organism
Life cycle: reproductive history of organism, from conception  production of own offspring
Fertilization and meiosis alternate in sexual life cycles
Meiosis: cell division that reduces # of chromosomes (2n  n), creates gametes
Fertilization: combine gametes (sperm + egg)
Fertilized egg = zygote (2n)
Zygote divides by mitosis to make multicellular diploid organism

33. Meiosis = reduction division
Cells divide twice
Result: 4 daughter cells, each with half as many chromosomes as parent cell

34. Meiosis I (1st division)
Interphase: chromosomes replicated
Prophase I:
Synapsis: homologous chromosomes pair up
Tetrad = 4 sister chromatids
Crossing over at the chiasmata
Metaphase I: Tetrads line up
Anaphase I:
Pairs of homologous chromosomes separate
(Sister chromatids still attached by centromere)
Telophase I & Cytokinesis:
Haploid set of chromosomes in each cell
Each chromosome = 2 sister chromatids
Some species: chromatin & nucleus reforms

36. Meiosis II (2nd division) = create gametes
Prophase II:
No interphase
No crossing over
Spindle forms
Metaphase II:
Chromosomes line up
Anaphase II:
Sister chromatids separate
Telophase II:
4 haploid cells
Nuclei reappear
Each daughter cell genetically unique

38. Events Unique to Meiosis I (not in mitosis)
Prophase I: Synapsis and crossing over
Metaphase I: pairs of homologous chromosomes line up on metaphase plate
Anaphase I: homologous pairs separate  sister chromatids still attached at centromere

39. Sources of Genetic Variation:
Crossing Over
Exchange genetic material
Recombinant chromosomes

40. Sources of Genetic Variation:
Independent Assortment of Chromosomes
Random orientation of homologous pairs in Metaphase I

41. Sources of Genetic Variation:
Random Fertilization
Any sperm + Any egg
8 million X 8 million = 64 trillion combinations!

42. Mitosis Meiosis Both are divisions of cell nucleus Somatic cells
2 diploid daughter cells
Clones
From zygote to death
Purpose: growth and repair
No synapsis, crossing over
Gametes
2 divisions
4 haploid daughter cells
Genetically different-less than 1 in 8 million alike
Females before birth follicles are formed. Mature ova released beginning puberty
Purpose: Reproduction

44. Varieties of Sexual Life Cycles

45. Alternation of Generations
Plant and some algae
Sporophyte (2n): makes haploid spores by meiosis
Spore  gametophyte by mitosis
Gametophyte (n): makes haploid gametes by mitosis

46. End of Review