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Cell Division

Cell Division. Your body is composed of more than a billion cells. Why must cells divide?. They are continually dying and must produce new cells An identical copy of your hereditary information is in the nucleus of each and every body cell called a somatic cell.

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Cell Division

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  1. Cell Division Your body is composed of more than a billion cells

  2. Why must cells divide? They are continually dying and must produce new cells An identical copy of your hereditary information is in the nucleus of each and every body cell called a somatic cell dbb.urmc.rochester.edu/.../photo_gallery.

  3. Chromosomes • The genetic information or blueprint that is organized into 46 chromosomes (each contains about one to two thousand genes)

  4. Karyotype Human chromosome number: 46 Karyotype – order of chromosomes from tallest to smallest.

  5. Every time a cell divides it must copy the chromosomes

  6. Goal of Mitosis Baby • is to allow for growth • maintain tissues Grow to adult

  7. Another way to look at this is like this:

  8. Stages of Mitosis is IPMAT Mitosis animation: http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

  9. Interphase • Time between divisions – cell spends 90% of its life here • DNA is copied here • Typical human cell divides every 24 hours

  10. Inside – looks like.. Diploid - 3 chromosome pairs, 6 individual chromosomes

  11. Your nucleus initially contained six un-replicated chromosomes, and now it contains six replicated chromosomes. • The two identical copies of each chromosome are calledsister chromatids • They remain attached at a point called thecentromere

  12. Prophase • Chromosomes condense (are visible) • Sister chromatids pair up. • Nuclear membrane disappears

  13. Pro-metaphase-Start moving to sides

  14. Metaphase • Paired chromatids line up in the middle of cell

  15. Anaphase • Chromatids are pulled into the apart. They are dragged through the cytoplasm (V-shaped)

  16. Telophase • Daughter chromosomes reach the poles • Cells start to separate • Nuclear membrane re-forms

  17. Cytokinesis (Cell Cutting) • The two daughter cells separate

  18. At the end of Mitosis, each daughter cell has an identical set of duplicate chromosomes They are called Somates – body cells

  19. Mitosis Stages Mitosis animation http://www.sumanasinc.com/webcontent/animations/content/mitosis.html

  20. Interphase is subdivided G1 – Gap 1 or growth 1 • cell carries out normal functions G1 is a period of activity in which cells do most of their growing, increasing in size and synthesizing new proteins and organelles

  21. S Synthesis – DNA is copied to prepare to divide • it synthesizes (to make) a duplicate set of DNA

  22. G2 G2 – Gap 2 • is where the organelles and molecules required for cell division are produced.

  23. M phase then Cytokinesis • Mitosis takes about an hour (most time spent during G1, S and G2 phase) PMAT

  24. Check points • G1 – Checks DNA damage before begins replication (S phase), if damaged then repaired or self destructs if cannot repair. • G2 – Checks DNA to see if properly copied during S phase • M – checks to ensure spindle fibers attach properly during metaphase • http://www.cellsalive.com/cell_cycle.htm

  25. How does Mitosis lead to Caner? Cancer is basically a disease of mitosis What is happening? The normal checkpoints that regulate mitosis are ignored or overridden by cancer cell.

  26. How does it occur? a change in function or a DNA mutation occurs in one of several genes (proteins) that normally function to control growth

  27. Result Once these crucial Cell Cycle genes start behaving abnormally, cancer cells start to proliferate wildly by repeated, uncontrolled mitosis Tumor production: http://www.youtube.com/watch?v=_ZEysIhDsok&feature=related

  28. Examples: • p53 protein can senses DNA damage and halts progression of cell cycle. Also known as tumor suppressor gene. However, p53 is mutated in over 50% of all human cancers.

  29. BRCA 1gene, the "Breast Cancer Gene"normally repairs mutations in PTEN gene which suppress tumor formation but if a gene contains mutations such that BRCA1 does not work properly, tumor formation can begin

  30. Meiosis • Cell Division to make sex cells (sperm and eggs) • Chromosome number is halved creating these cells • ex. 46  23 Meiosis animation: http://www.sumanasinc.com/webcontent/animations/content/meiosis.html

  31. Diploid vs. Haploid Diploid – two or a pair of chromosome Haploid – 1 set of chromosomes Examples: Diploid = 2 4 8 Haploid = 1 2 4 YOU TRY: If the diploid chromosome number is 28, what is the haploid number?

  32. Stages : IPMAT then PMAT II Crossing Over (independent Assortment) - tetrad

  33. Crossing Over • Homologous chromosomes can swap information, increasing variability in offspring • Takes place in prophase Tetrad – set of 4 chromosomes

  34. Homologous Chromosomes • The two versions of each chromosome • One from mom, one from dad

  35. Gametes Gametes are sex cells Sperm Egg Each are haploid – half the number of original set of chromosomes Diploid = 46 Haploid = 23

  36. Spermatogenesis • Creates four functional sperm cells

  37. Oogenesis • Creates one functional Ovum (egg) and 3 polar bodies

  38. Gametes – sex cells Products of meiosis in males formed in testes? A: 4 sperm Products of meiosis in females formed in ovaries? A: 1 functional egg (the other 3 cells are not functional and are reabsorbed by the body? Humans have 46 homologous chromosomes (23 pairs)

  39. Stages of Meiosis Interphase: same as Mitosis Prophase 1: Same except for Crossing - over can occur – leads to independent assortment (life is a box of chocolates) Metaphase 1: Same except that form a tetrad Homologous chromosomes that align at the equatorial plate. Anaphase 1: Same except that the Homologous pairs separate with sister chromatids remaining together. Telophase 1: Same except each daughter contains only one chromosome of the homologous pair (not a pair of chromosomse).

  40. Second Stage Prophase 2: same as mitosis Metaphase 2: same as mitosis Anaphase 2: Centromeres divide and sister chromatids migrate separately to each pole. (same as mitosis) Telophase 2: Four haploid daughter cells instead of two. . Daughter cells have half the number of chromosomes found in the original parent cell and with crossing over, are genetically different.

  41. Timing in Meiosis When do Females produce their eggs? • Prior to birth What do Males produce sperm? • Once hit puberty • Helpful saying I don’t use “Mi-Toes-es” for making sperm or eggs!

  42. Differences between Mitosis and Meiosis MitosisMeiosis IPMAT IPMAT I & PMAT II Diploid Haploid Somate Gamete 2 cells 4 cells

  43. Non-Disjunction- when chromosomes do not separate correctly during meiosis. End up with 47 or 45 in each new cell. Example: Downs Syndrome = Trisomy 21 (3 chromosomes 21) Turner’s Syndrome = one X and no second sex chromosome

  44. Trisomy 21

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