The document discusses cell replication in prokaryotes and eukaryotes. It notes that binary fission in bacteria is much faster than mitosis in eukaryotic cells, taking approximately 20 minutes versus several hours. The document then provides details on the stages of binary fission in bacteria and the cell cycle in eukaryotic cells, including interphase, mitosis, and cytokinesis. It describes DNA replication and the checkpoints between stages to ensure errors are corrected. A lack of functioning checkpoints can lead to uncontrolled cell division known as cancer.

1. CELL REPLICATION(in prokaryotes & eukaryotes)

2. Binary fission in bacteriaMuch faster than mitosis in eukaryotic cellsTakes approx. 20 mins as opposed to several hoursIf resources were available once cell could become 16,000,000 in 8 hours!

3. Binary Fission in bacteria

4. Binary Fission in bacteriaBidirectional replication of circular DNA

5. Binary Fission in bacteriaDNA moves to poles

6. Binary Fission in bacteriaCell elongatesCleavage furrow forms

7. Binary Fission in bacteriaCell divides

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

9. AnimationsAnimation 1Animation 2

10. The Cell Cycle – G1The first phase is a growth phase (G1)The new cell starts growing and replicating its organellesAt 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.

11. The Cell Cycle - SDuring the synthesis (S) phase, DNA replication occurs

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

18. DNA ligse sticks together prefabricated ‘Okazaki’ fragments made by DNA polymerase to replace the RNAThe Cell Cycle – G2During the next growth phase (G2), the cell continues to grow in preparation for divisionThe checkpoint during this phase is extremely important.If any errors have occurred during transcription, the cell must undergo apoptosis (programmed cell death)

19. The Cell Cycle - MDuring 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 - CCytokynesis (C) is actually the last part of MitosisAt 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. CANCERCells 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 division2N - 4NAnimal & Plant Cells Nucleus clearly definedChromosomes not yet visibleDNA replicatedOrganelles replicatedCell increases in size

25. InterphasePlant CellAnimal CellPhotographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

26. ProphaseThe cell prepares for nuclear division4NAnimal & Plant CellsDNA packaged in to chromosomesNuclear envelope disappearsCentrioles move to opposite sides of the cell

27. ProphasePlant CellAnimal CellPhotographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

28. MetaphaseThe cell prepares chromosomes for division4NAnimal & Plant CellsChromosomes line up at the center of the cellSpindle fibres attach to centromeres on the chromosomesCentrioles reach the opposite poles of the cell

29. MetaphasePlant CellAnimal CellPhotographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

30. AnaphaseThe chromosomes divide4NAnimal & Plant CellsSpindle fibers contract and pull chromosomes apart½ of each chromosome (called a chromatid) moves to each hemisphereUnattached spindle fibres push against each other or the sides of the cell, and it begins to elongate

31. AnaphasePlant CellAnimal CellPhotographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

32. TelophaseThe cytoplasm divides4N - 2NPlant CellDNA spreads out2 nuclei formCell plate forms new cell wall between the nuclei to form the 2 new daughter cellsAnimal CellDNA spreads out2 nuclei formContractile ring causes a cleavage furrow to form the 2 new daughter cells

33. TelophasePlant CellAnimal CellPhotographs from: http://www.bioweb.uncc.edu/biol1110/Stages.htm

34. MitosisAnimationsMitosis.exeMitosis Animation

35. Animal Mitosis -- Review

36. Plant Mitosis -- Review

37. Summary of MitosisProphase: Chromosomes condenseNuclear envelope disappearscentrosomes move to opposite sides of the cellSpindle forms and attaches to centromeres on the chromosomesMetaphaseChromosomes lined up on equator of spindlecentrosomes at opposite ends of cellAnaphaseCentromeres divide: each 2-chromatid chromosome becomes two 1-chromatid chromosomesChromosomes pulled to opposite poles by the spindleTelophaseChromosomes de-condenseNuclear envelope reappearsCytokinesis: the cytoplasm is divided into 2 cells

38. MEIOSIS

39. Recombination through meiosisDNA replicatesCrossing overRandom assortmentFirst divisionSecond random assortmentSecond division

40. Mitosis vs. meiosis

41. Getting the names rightCentromereSpindle fibres / microtubulesKinetochoreSister chromatids

42. Recombination = variation2 pairs of chromosomes = 4 possibilities

43. 4 pairs of chromosomes = 8 possibilities

44. What are the chances of identical offspring?

45. 2n = 46 (not incl. twins) 1 / 16,777,216DNA ReplicationDNA is uncoiled and unzipped by helicase & gyraseThe original strands are called the template strandsThe new strands are called the complementary strandsThe 3’ to 5’ template strand is the leading strandThe 5’ to 3’ template strand is the lagging strandThe complementary strand can only be written 5’ to 3’DNAi ANIMATIONS x 2

46. The leading strandAn RNA primer is put down by RNA polymeraseComplementary DNA is put down base-pair by base-pair by DNA polymeraseDIRECTION OF REPLICATION3’ 5’RpDp5’3’

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

48. The lagging strandRNA PolymeraseDNA Polymerase IIIDNA Polymerase IDNA LigaseDIRECTION OF REPLICATION5’ 3’3’5’

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

50. Biozone Fun!DNA replicationpp. 203-25Cell cycle, mitosis, apoptosispp. 209-212Meiosispp. 287-290