Cell Division: DNA Replication and Mitosis Explained

1. Level 2

2. Remember… *DNA more stable than RNA * All organisms must be able to reproduce to keep life going Cell Division

3. One cell becoming two

4. All Reproducing Cells • 1. Replicate DNA in parent cell during the S phase. • 2.Replicate organelles • 3. Perform cytokinesis- division of cytoplasm and cell membrane. • Cyto – cell, kinesis- movement

5. Reasons for Cell Division • In unicellular organisms it is primarily for reproduction of themselves. • In multicellular organisms it is for reproduction, growth, and repair of tissues. • If cells do not divide, they get to big. • Two major problems with big cells: • DNA cannot code for all of the necessary functions • Substances cannot enter and exit fast enough.

6. Figure 9.3 The Eukaryotic Cell Cycle Cytokinesis Preparing for mitosis Commitment to cell division S phase-

8. Three Reasons for Cell Division

9. Four Events that Must occur for Cell Division • A reproductive signal (intracellular/extracellular) to initiate division. • Replication of DNA, so the new cells match identically to old cell. • Segregation- process by which DNA is passed to each of the two resulting new cells. • Cytokinesis- process by which the cell membrane and cell wall separate into two new cells.

10. Binary Fission • In prokaryotes, the entire single-celled organism divides. • First it doubles in size, then duplicates its DNA, and then divides. • In prokaryotes, the initiating reproductive signal is thought to be environmental conditions and food supply

11. DNA Replication in Prokaryotes (S phase) • Most prokaryotes only have one chromosome, and it is circular . • Circular chromosomes are also in chloroplasts, mitochondria, and viruses. • ori- origin site of DNA replication • ter- terminus of DNA replication

12. Figure 9.2 Prokaryotic Cell Division (Part 1)

13. Prokaryotic DNA Replication • Referred to as circular or theta replication. • Cleavage furrow follows after replication • The two resulting cells are clones= identical cells. • Mitosis is thought to have evolved from binary fission…commonality: synthesis and division

14. Eukaryotic Cell Division • Most complex eukaryotes originate from a single cell: fertilized egg. • The formation of a multicellular organism from a fertilized egg is known as development. • Eukaryotic cell division are driven by the needs of the organism, not the environmental conditions and food supply.

15. Somatic cells vs. Germ cellsThe egg surrounded by sperm.

16. Eukaryotic Cell Division • Eukaryotic cells also have more chromosomes to duplicate. • Eukaryotes have a nucleus that needs to divide before cytokinesis can take place. This is called mitosis. • Mitosis is the division of the nucleus. • Cytokinesis is the division of everything but the nuclear contents. Different in plants than animals

17. Control of Mitosis in Eukaryotes • Cell cycle- the events that occur to produce two eukaryotic cells from one. • Cell cycle has two main phases: Interphase 90-95% of time, Mitosis 5% of time. • Cell types vary with how long they live in interphase. • Mitosis and cytokinesis are referred to as the M phase of the cell cycle, but cytokinesis always follows mitosis.

18. DNA Division • Genome- term for all genetic material in a cell. • In humans the genome is 7ft./cell • DNA has 2 appearances: • Chromatin • Chromosome

19. Somatic Cells vs. Germ Cells • Perform mitosis • Parent cell2 identical daughter cells • 1 division following S phase • 2n or diploid • Humans =46 • Perform meiosis • Germ cell 4 non-id. Cells • 2 divisions following S phase • n or haploid • Makes gametes: egg/ sperm • Humans =23 Somatic Cells Germ Cells

20. Data Set Question 1 U3,D1

21. Remember cell movement… • Cytoskeleton is composed of microtubules, microfilaments, and intermediate filaments. • Centrioles are a part of cytoskeleton made of microtubules. • Microtubules also make up spindle fibers • Proteins will also move things

22. Centrioles

23. Interphase

24. Cell Cycle • G1- first growth, everyday activity, first checkpoint will be passed…point of no return. • S- DNA replicates, (46-92 in humans: 4n) • G2- second growth, second checkpoint where all DNA is proofed and organelles checked for cell division.

25. Mitosis • Mitosis is the segregation step (3) for eukaryotic cells. • Sister chromatids = replicated DNA. • Chromatids held together by cohesion-protein complex, found at centromere.

26. Before and after the S phase

27. Figure 9.7 Chromosomes, Chromatids, and Chromatin

28. Histones • Web-like proteins that have a positive charge, and interact with the negative phosphates of DNA. • Histones form nucleosomes. • Eight histone molecules. • 146 base pairs of DNA • Histone One H1. Clamps DNA to histone core. • Chromatin will condense until chromatids move apart in anaphase.

29. Figure 9.8 DNA is Packed into a Mitotic Chromosome (Part 1)

30. Centrosomes • Centrosomes consist of a pair of centrioles. Centrioles are hollow tubes consisting of nine microtubules. Each centriole pair is situated perpendicular to one another. • At G2M phase, the centrosomes migrate to opposite ends of the cell. • Plant cells do not have centrosomes, just have a microtubule organization center.

31. Mitosis is division of the nucleusMitosis AnimationMitosis-Good Animation

32. Interphase cell (Look at the chromatin in the blue nucleus and the yellow cytoskeleton.)

33. Mitosis Step 1: Prophase • Nuclear membrane begins to break down • Cohesion proteins are removed from chromatin, except at centromere, and the chromatids become distinctly visible. • Kinetochores (proteins) develop at centromere region • Microtubules extend from centrioles, forming spindle fibers.

34. Cell in Prophase

35. Prometaphase • Not officially step two. • Nuclear membrane completely disappears, as well as nucleolus

36. Figure 9.10 Mitosis (Part 1)

37. Metaphase • This is when all the centromere are in the middle of the cell at the equatorial plate. • Chromosomes are maximally condensed at this phase. • At the end of metaphase all chromatid pairs will separate simultaneously. This is the third checkpoint.

38. Cell in Metaphase

39. Anaphase • Sister chromatids begin to separate. • Sister chromatids separate into sister chromosomes. • Separation of chromatids is accomplished by a protease called separase hydrolyzing the cohesion proteins at the centromere. • Separase is controlled by a competetive inhibitor. • Spindle Checkpoint- when all kinetochores are attached to s.f. then separase becomes activated.

40. Cell in Anaphase

41. Figure 9.11 Chromatid Attachment and Separation

42. Anaphase • Movement of sister chromosomes away from one another is accomplished in two ways. • 1. Daughter chromosomes will propel themselves towards opposite centrosome poles (ATPADP) • 2. Spindle fibers will shorten drawing the sister chromosomes to opposite ends of the cell. • This process takes ~10min. to one hour.

43. Telophase • When sister chromosomes stop moving, the cell enters telophase. • Spindle fibers begin to break down and reform the nuclei. • Nuclear membranes and nucleoli reform around the two sets of DNA. • Mitosis is complete (segregation of DNA accomplished)

44. Cell in Telophase and starting Cytokinesis

45. Figure 9.10 Mitosis (Part 2)

46. Cytokinesis • The end of telophase is two nuclei in one cell; therefore, the cell needs to divide. • Cytokinesis is the process of cytoplasm division. • Animal cells divide by the cell membrane furrowing. Contraction of actin and myosin microfilaments. • Plant cells’ vesicles from the Golgi bodies, move to equatorial plate, fuse to form new C.M. Vesicle contents also create a cell plate, which becomes new cell wall.

47. Figure 9.12 Cytokinesis Differs in Animal and Plant Cells

48. Cell Cycle REGULATION • Critical for normal growth and development • Controlled by proteins called cyclins. • 3 Checkpoints:

49. Compare the difference between Theta and Eukaryotic Division • Gene # • Gene Combinations • Linking Genes • Species Variation • Inheritance from parents

50. Cyclins and Proteins trigger Cell Division • Cyclin- protein that causes G1SG2 transition. (s phase to anaphase [inc.]) • Kinase is an enzyme that turn on cell processes • Cyclin + Kinase = Cdk aka MPF • MPF-Maturation Promoting Factor