Chapter 10: Cell Division & Mitosis

1. Chapter 10: Cell Division & Mitosis

2. Mitosis • Division of cell nucleus • Common to ALL living things-- but details of mitosis vary from organism to organism • The sequence of phases is fixed in all organisms, but time spent in each phase varies

3. Biologists Compare Cell Division • In different organisms by comparing their cell cycles • Between different kinds of tissues within the animal/plant • Between normal tissue and tissue repair after injury • Between the young child and elderly person

4. Biologists Compare Cell Division cont. 5) Between embryological (unspecialized cells) and in fetal cells that develop into tissues (specialized cells) 6) Between prokaryotic and eukaryotic cells - Prokaryotic & some protists binary fission 7)Between cancer and normal cells

5. Cell Division in Eukaryotes • Unicellular organisms– cell division  new individuals (reproduction) • Multicellular organisms-- cell growth/ repair/ maintenance/ reproduction • Plants- formation of roots, stems, leaves • Animals- formation of specialized cells (nerve, bone, muscle)– blood and skin cells are replaced as needed throughout life (106 mitotic cell division/sec)

6. Cell Division in Eukaryotes cont. 3) In all cell divisions there is chromosome replication/ duplication - Body/ somatic cells= 46 chromosomes (23 pairs/ 1 set from each parent) - Gametes/ sex cells= 23 chromosomes (1 set from parent)

7. Controls of Cell Division ( Cell Cycle) • Rate varies between species and between tissues within same organism-anywhere from min/hr/day/never • GoPhase • Cells never leave G1 phase • In this way, specialized cells remain very active-- never having to stop working to divide; all energy is used to carry out important specialized functions Ex: Nerve and muscle cells (can enlarge through use of anabolic steroids), Heart cells (can enlarge in athletes), Leaf cells (palisade, xylem, phloem), Red blood cells (in circulation) complete cycle only in growth tissues

8. Controls of Cell Division ( Cell Cycle) cont. b. Some cells divide very rapidly Ex: Bacteria E. coli (prokaryote- every 30 min) Skin and blood (106 div/sec) Digestive tract (6 hrs) Respiratory tract (8 hrs)

9. Controls of Cell Division ( Cell Cycle) cont. 2) Could be caused by some “trigger protein”-- some molecular on/off switch like a hormone of an enzyme - Turned on rapidly in times of cell stress or gradually increases during G1 phase to a level when S phase can begin

10. Controls of Cell Division ( Cell Cycle) cont. 3) Or by special regions called TELOMERES-- found at the ends of chromosomes - These telomeres shorten with every subsequent division until division stops • Changes seen in normal/ cancer cells • Changes seen in early aging (Progeria)/ normal

11. Overview of Cell Cycle

12. Phases of Cell Cycle • Sequence is fixed from start to finish (for entire life cycle) • Interphase (non-dividing cells) has 3 distinct phases: G1, S, G2 • Mitosis (dividing cells) has 4 phases in nucleus: P, M, A, T • Cytokinesis: C

13. Phases of Cell Cycle cont.

14. INTERPHASE (3 phases) • G1 phase(Growth 1- just after cell is formed) • Very active metabolically-- biochemical pathways: photosynthesis, cell respiration, biosynthesis • ↑ in molecules-- enzymes, hormones, proteins, mRNA • ↑ in number of cellular organelles • ↑ in size-- usually doubles in size • Length varies from hours to several days

15. INTERPHASE (3 phases) • S phase (Synthesis- must occur prior to mitosis) • DNA double exactly (replication) all genes copies • DNA polymerase (enzyme) is very active-- nucleotide assembly • Histone proteins (for DNA support) increase • Nucleosomes formed (DNA packing occurs) • Usually 3-6 hours • 2 chromatids attached at centromere-- end result

17. INTERPHASE (3 phases) 3) G2 phase (Growth 2- getting ready for division) • Twice as much DNA as G1 • Protein synthesis (microtubules/ microfilaments) form spindles • Centriolesreplicate (in animal cells only) • 2-5 hours, relatively constant among cells

18. MITOSIS (P, M, A, T) • Phases covered later

19. CYTOKINESIS • Division of the cytoplasm • Occurs during telophase of mitosis

20. 2 Major Phases of Mitotic Cell Division • MITOSIS • Process of cell division in eukaryotic cells in which the nucleus is divided into 2 nuclei, each with the same number and kinds of chromosomes • This phase is divided into the: • Growth period-- Interphase • And 4 stages-- Prophase, Metaphase, Anaphase, Telophase (P,M,A,T) • The stages conserve chromosome number by equally distributing replicated chromosomes to each of the daughter cells

21. 2 Major Phases of Mitotic Cell Division cont. 2) CYTOKINESIS • The division of the cytoplasm to form 2 separate daughter cells immediately after mitosis

22. MITOSIS (replication and division of the nucleus) • INTERPHASE • G1 phase • Growth phase of a cell • Cell grows rapidly and carries out its routine functions • For most organisms, this phase occupies the major portion of the cell’s life between cell divisions • S phase • Time during which DNA is being replicated • At the end of this phase, an individual chromosome consists of 2 chromatids attached by a centromere

23. MITOSIS – INTERPHASE cont. c. G2phase • Time during which preparations are made for nuclear division • Mitochondria and other organelles replicate • Microtubules reassembled-- will be used to form the spindle apparatus that moves the chromosomes d. M phase • Phase where mitosis occurs • Mitosis is the replication and division of the nucleus to form 2 identical nuclei, each with the same number and kinds of chromosomes

24. Cell Cycle

25. Interphase

26. MITOSIS 2) PROPHASE: 2 Major Phases • Early Prophase • Replicated chromatids are present • Replicated centrioles (only in animal cells) migrate to opposite poles of the cell • Spindle fibers become visible • Late Prophase • Nucleolus and nuclear envelope disintegrate • Chromatids condense to form dense coils

27. Prophase

28. MITOSIS cont. 3) METAPHASE • Chromatids are at the same midline (called the equatorial plate in plants) • Spindle fibers are very dense • In animal cells, the aster is visible around the centrioles

29. Metaphase

30. MITOSIS cont. 4) ANAPHASE • Centromeres separate and the chromatids now become individual chromosomes • Chromosomes migrate to opposite poles of the cell

31. Anaphase

32. MITOSIS cont. 5) TELOPHASE • Phase of mitotic cell division in which the cytoplasm divides and 2 identical cells form • Cytokinesis occurs during this phase

33. 2 Major Differences Between Animal and Plant Cell Division

34. Animal vs Plant

36. MITOTIC CELL DIVISION IN PLANT CELLS

37. MITOTIC CELL DIVISION IN PLANT CELLS cont.

38. MITOSIS

39. PRACTICE! Name that Stage!

40. PRACTICE! Name that Stage!

41. PRACTICE! Name that Stage!

42. PRACTICE! Name that Stage!