1. CELL REPLICATION (in prokaryotes & eukaryotes)

2. Binary fission in bacteria Much faster than mitosis in eukaryotic cells Takes approx. 20 mins as opposed to several hours If resources were available once cell could become 16,000,000 in 8 hours!

3. Binary Fission in bacteria

4. Binary Fission in bacteria Bidirectional replication of circular DNA

5. Binary Fission in bacteria DNA moves to poles

6. Binary Fission in bacteria Cell elongates Cleavage furrow forms

7. Binary Fission in bacteria Cell divides

8. The Cell Cycle – Eukaryotic cells Final checkpoint at the end of metaphase

9. Animations Animation 1 Animation 2

10. The Cell Cycle – G1 The first phase is a growth phase (G1) The new cell starts growing and replicating its organelles At the end of G1, the checkpoint is to gauge if it is a good time for cell to keep growing or dividing or if a delay is necessary. If the cell is under any sort of stress, it will pause at this stage.

12. It is at this point that the diploid cell (2n) doubles to 4n, so that when it divides there will be two complete copies of the DNA

13. DNA replication is semi-conservative – every new molecule consists of one original strand and one new strand.

14. DNA replication involves numerous enzymes

15. Helicase and gyrase unwind and unzip to strands of DNA

16. DNA polymerase continuously adds nucleotides to the leading strand in a 5’ to 3’ direction

17. RNA primase makes an RNA primer on the lagging strand

19. The Cell Cycle - M During Mitosis (M), the single parent cell gives rise to two identical daughter cells. Another checkpoint occurs at the end of metaphase to ensure that chromosomes are aligned and that spindle fibres are attached corectly. A negative result at the checkpoint here will result in apoptosis.

20. The Cell Cycle - C Cytokynesis (C) is actually the last part of Mitosis At this point the cell, which momentarily has twin nuclei, will divide in to two new cells (2n) and the process will begin again.

21. What happens if the checkpoints don’t work? If cell cycle checkpoints are operated by enzyme proteins. These enzymes can be prevented from carrying out normal function by inhibitors. These enzymes could also be stimulated to maintain an active state permanently. Either way can lead to uncontrolled and unmonitored cell division, this is commonly known as ….

22. CANCER Cells multiply uncontrollably and regardless of accumulating errors will never apoptose. Does not form useful cells as cells spend far more time in division rather than growth (a reversal of the normal situation).

23. MITOSIS

24. InterphaseThe cell prepares for division 2N - 4N Animal & Plant Cells Nucleus clearly defined Chromosomes not yet visible DNA replicated Organelles replicated Cell increases in size

25. Interphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

26. ProphaseThe cell prepares for nuclear division 4N Animal & Plant Cells DNA packaged in to chromosomes Nuclear envelope disappears Centrioles move to opposite sides of the cell

27. Prophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

28. MetaphaseThe cell prepares chromosomes for division 4N Animal & Plant Cells Chromosomes line up at the center of the cell Spindle fibres attach to centromeres on the chromosomes Centrioles reach the opposite poles of the cell

29. Metaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

30. AnaphaseThe chromosomes divide 4N Animal & Plant Cells Spindle fibers contract and pull chromosomes apart ½ of each chromosome (called a chromatid) moves to each hemisphere Unattached spindle fibres push against each other or the sides of the cell, and it begins to elongate

31. Anaphase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

32. TelophaseThe cytoplasm divides 4N - 2N Plant Cell DNA spreads out 2 nuclei form Cell plate forms new cell wall between the nuclei to form the 2 new daughter cells Animal Cell DNA spreads out 2 nuclei form Contractile ring causes a cleavage furrow to form the 2 new daughter cells

33. Telophase Plant Cell Animal Cell Photographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

34. MitosisAnimations Mitosis.exe Mitosis Animation

35. Animal Mitosis -- Review

36. Plant Mitosis -- Review

37. 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

38. MEIOSIS

39. Recombination through meiosis DNA replicates Crossing over Random assortment First division Second random assortment Second division

40. Mitosis vs. meiosis

41. Getting the names right Centromere Spindle fibres / microtubules Kinetochore Sister chromatids

43. 4 pairs of chromosomes = 8 possibilities

44. What are the chances of identical offspring?

46. The leading strand An RNA primer is put down by RNA polymerase Complementary DNA is put down base-pair by base-pair by DNA polymerase DIRECTION OF REPLICATION 3’ 5’ Rp Dp 5’ 3’

47. The lagging strand RNA polymerase puts down primers along the template strand of DNA DNA polymerase III builds short ‘Okazaki’ fragments from each primer DNA polymerase I removes the RNA and replaces it with DNA DNA ligase sticks the fragments together

48. The lagging strand RNA Polymerase DNA Polymerase III DNA Polymerase I DNA Ligase DIRECTION OF REPLICATION 5’ 3’ 3’ 5’

49. Additional info on cell reproduction Our cells can be categorised in to two types Somatic cells (diploid) Germline cells (diploid but give rise to haploid gametes – sperm & eggs)

50. Biozone Fun! DNA replication pp. 203-25 Cell cycle, mitosis, apoptosis pp. 209-212 Meiosis pp. 287-290