Bft1033 1 mitosis_print1


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Bft1033 1 mitosis_print1

  1. 1. Cellular Reproduction and the Cell Cycle Mitosis
  2. 2. Why do cells divide?  Growth  Development  Repair.
  3. 3. Cell division  All complex organisms originated from a single fertilised egg  Every cell in your body started here, through cell division the numbers are increased  Cells then specialise and change into their various roles.
  4. 4. Essential Features of Cell Division  Transmit a complete copy of genetic information (DNA)  Transmit materials necessary for cell to survive and use genetic information.
  5. 5. Two Fundamental Types of Cells (Organisms)  Prokaryotes  Eukaryotes.
  6. 6. Prokaryotic Cell  No nucleus – genetic material (DNA) in cytoplasm  No membrane-bound organelles  Cell division is called binary fission  Example: bacteria.
  7. 7. Prokaryotic Cell  Rod-Shaped Bacterium, E. coli, dividing by binary fission
  8. 8. Prokaryotic Cell Rod-Shaped Bacterium, hemorrhagic E. coli, strain 0157:H7
  9. 9. Prokaryotic Cell
  10. 10. Eukaryotic Cell  Membrane-bound organelles, including a nucleus  Genetic material (DNA) contained within the nucleus  Cell division of somatic cells called mitotic cell division  Examples: fungi, protists, plants, animals.
  11. 11. Eukaryotic Cell
  12. 12. What is Mitotic Cell Division?  Division of somatic cells (non reproductive cells) in eukaryotic organisms  A single cell divides into two identical daughter cells ◦ Maintains chromosome ploidy of cell.
  13. 13. Ploidy Level  Ploidy – refers to the number of pairs of chromosomes in cells  haploid – one copy of each chromosome – designated as “n”  diploid – two copies (=pair) of each chromosome – designated as “2n”  triploid – three copies of each chromosome – designated as “3n”
  14. 14. Number of Chromosomes  Each species has a characteristic number of chromosomes: ◦ ◦ ◦ ◦ ◦ ◦ Prokaryotes = one chromosome Crayfish (2n) = 200 chromosomes Fruit fly (2n) = 8 chromosomes Human (2n) = 46 chromosomes Wheat (6n) = 42 chromosomes Potato (4n) = 48 chromosomes.
  15. 15. Number of Chromosomes  Diploid organisms receive ◦ ◦ one set of chromosomes from female parent (= maternal) one set of chromosomes from male parent (= paternal)  A “matched” pair of maternal and paternal chromosomes are called homologues gamete (n) zygote (2n) fertilization gamete (n)
  16. 16. Structure of a eukaryotic chromosome unreplicated chromosome arm arm centromere
  17. 17. Structure of a eukaryotic chromosome  Prior to cell division:  chromosomes (DNA) are replicated (duplicated)  duplicated chromosome ◦ ◦ attached at their centromeres as long as attached, known as sister chromatids duplicated chromosome sister chromatids
  18. 18. Structure of a eukaryotic chromosome
  19. 19. Structure of a eukaryotic chromosome metacentric submetacentric acrocentric telocentric
  20. 20. Structure of a eukaryotic chromosome sister chromatids daughter chromosomes
  21. 21. The Cell Lifecycle  The cell lifecycle is well defined and can be divided into four stages: ◦ Gap 1 (G1) - The growth phase in which ◦ ◦ ◦ most cells are found most of the time Synthesis (S) - During which new DNA is synthesized Gap 2 (G2) - The period during which no transcription or translation occurs and final preparations for division are made Mitosis - Cell division.
  22. 22. The Cell Lifecycle Gap 1 - Doubling of cell size. Regular cellular activities. transcription and translation etc. Synthesis of DNA Regular cell activities cease and a copy of all nuclear DNA is made S G1 G2 M Gap 2 - Final preparation for division Mitosis - Cell division
  23. 23. Cell Division Mitosis
  24. 24. Mitosis  Mitosis is the process by which new body cell are produced for: ◦ Growth ◦ Replacing damaged or old cells  This is a complex process requiring different stages.
  25. 25. The Cell Lifecycle G1 S G2 M
  26. 26. Stages of Mitosis  During mitosis an exact copy of the genetic material in the “mother” cell must be distributed to each “daughter” cell  Each stage of mitosis is designed to achieve equal and exact distribution of the genetic material which has been copied during the S phase of the cell cycle.
  27. 27. Stages of Mitosis  Interphase - The ‘in between’ stage - this is the stage most cells spend their time in doing the things that cells do and, if they are preparing to divide, growing and replicating their DNA S Interphase G2 G1 M
  28. 28. Mitosis     Prophase Metaphase Anaphase Telophase.
  29. 29. Prophase The chromosomes condense  The nuclear envelope and nucleolus disappear  The centrosomes move to opposite poles  The spindle starts to form, growing out of the centrosomes towards the chromosomes. 
  30. 30. Metaphase Metaphase is a short resting period  the chromosomes are lined up on the equator of the cell  with the centrosomes at opposite ends and the spindle fibers attached to the centromeres  Everything is aligned for the rest of the division process to occur. 
  31. 31. Anaphase  In anaphase, the centromeres divide at this point, each individual chromosome goes from: ◦ 1 chromosome with 2 chromatids ◦ to: ◦ 2 chromosomes with one chromatid each  Then the spindle fibers contract, and the chromosomes are pulled to opposite poles, towards the centrosomes.
  32. 32. Telophase In telophase the cell actually divides  The chromosomes are at the poles of the spindle  The spindle disintegrates  The nuclear envelope reforms around the two sets of chromosomes  The cytoplasm is divided into 2 separate cells, the process of cytokinesis. 
  33. 33. Cytokinesis  The organelles get divided up into the 2 daughter cells passively: they go with whichever cell they find themselves in  In plant cells, a new cell wall made of cellulose forms between the 2 new nuclei, about where the chromosomes lined up in metaphase ◦ Cell membranes form along the surfaces of this wall  In animal cells, a ring of actin fibers forms around the cell equator and contacts, pinching the cell in half.
  34. 34. Cytokinesis
  35. 35. Summary of Mitosis  Prophase: ◦ ◦ ◦ ◦  Chromosomes condense Nuclear envelope disappears centrosomes move to opposite sides of the cell Spindle forms and attaches to centromeres on the chromosomes Metaphase ◦ Chromosomes lined up on equator of spindle ◦ centrosomes at opposite ends of cell  Anaphase ◦ Centromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomes ◦ Chromosomes pulled to opposite poles by the spindle  Telophase ◦ Chromosomes de-condense ◦ Nuclear envelope reappears  Cytokinesis: the cytoplasm is divided into 2 cells.
  36. 36. 