LECTURE 8: MITOSIS AND CYTOKINESIS

1. LECTURE 8: MITOSIS AND CYTOKINESIS

2. INTRODUCTION • Cell division is accomplished by • mitosis = division of chromosomes and • cytokinesis = division of the cytoplasm • Mitosisis the division of somatic cells in which the appropriate number of chromosomes is maintained • A somatic cell is a body cell of an organism or a cell that is not involved in reproduction of a new organism. Somatic cells divide to recreate themselves

3. Cytokinesis is division of the cytoplasm to produce two daughter cells, usually begun during telophase Difference between animals and plants: plants are divided by the formation of a cell plate, where animal cells are divided through the formation of a cell cleavage. Cell plate materials originate in the golgi complex.

4. INTRODUCTION  When the somatic cell has its complete complement of chromosomes it is said to be in the diploid condition At the end of mitosis daughter cells are diploid Terminology Genome : cell’s genetic information Somatic : body cells Gametes : reproductive cells (sperm and egg cells) Chromosomes : DNA molecules Diploid (2n) : 2 sets of chromosomes Haploid (1n) : 1 set of chromosomes

5. BASIC PRINCIPLECell Division: Key Roles

6. Coordination of Mitosis and Cytokinesis Cell Division demands coordination of DNA replication (Mitosis) and division of the cytoplasm (Cytokinesis). Cell Division at cellular level

7. What’s so important about cell division? The process

8. prophase interphase metaphase The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions.

9. Mitosis Precisely and Evenly Divides Duplicated Chromosomes Cytokinesis is the process of cell division and it is distinct and separable from mitosis.

10. In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells Cleave furrow in a dividing frog cell.

11. The Plant Cell Wall Forces Cytokinesis to Play by Different Rules

12. Cancer Transformation Tumor: benign or malignant Metastasis

13. Cancer Is One Outcome of A Runaway Cell Cycle Licentious division - prostate cancer cells during division.

14. Chromosome and DNA What is the difference between DNA and Chromosome? What is Karyotype ?

15. Cell Devision at chromosome level CHROMOSOME DUPLICATION AND SEPERATION

16. DNA Replication – Simple in Principle, Complicated in Practice Cell Devision at DNA level

17. duplicated chromosome chromatin DNA is Packaged into Chromosomes DNA in the cell is virtually always associated with proteins. The packaging is impressive – 2 meters of human DNA fit into a sphere about 0.000005 meters in diameter.

18. The Link Between DNA Replication and Chromosome Duplication

19. DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell. 95% of the time, chromosomes are like this.

20. A Karyotype is an arranged picture of chromosomes at their most condensed State A normal human karyotype Note that almost all chromosomes come in homologous pairs. Boy or girl?

21. The Cell Cycle

22. From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle In multicellular organisms like us, progress through the cell cycle is carefully regulated.

23. The Cell Cycle Interphase (90% of cycle) G1 phase~ growth S phase~ synthesis of DNA G2 phase~ preparation for cell division Mitotic phase Mitosis~ nuclear division Cytokinesis~ cytoplasm division INTERPHASE - It is the time between divisions

24. The Cell Cycle G1 S G2 Mitosis & cytokinesis

25. Cell Cycle regulation Growth factors Density-dependent inhibition Anchorage dependence

26. Stages of Mitosis

27. Mitosis Prophase Prometaphase Metaphase Anaphase Telophase

28. Mitosis in Action Blue shows DNA, green shows spindle fibers.

29. Stages of mitosis

30. Stages of mitosis

31. PROPHASE, METAPHASE, ANAPHASE,TELOPHASE 1. Prophase: Chromosomes condense and become visible, each Chromosome contains several cm of DNA condensed into 5 – 10 micrometers. During the S Phase each chromosome has been duplicated into a sister chromatid. (A chromotid is one of the two halves of duplpicated chromosomes) S Phase = synthesis of DNA

32. Prometaphase Nuclear membrane fragments Spindle interaction with chromosomes Kinetochore develops

33. Centrosomes at opposite poles Centromeres are aligned Kinetochores of sister chromatids attached to microtubules (spindle) • 2. Metaphase: • Chromosomes line up along the cell “equator”. • The cell itself condenses and the chromosomes are more clearly visible than during any other phase of mitosis

34. Paired centromeres separate; sister chromatids liberated Chromosomes move to opposite poles Each pole now has a complete set of chromosomes • 3. Anaphase • is defined as the sister chromatids begin to separate • By now each chromatid is an independent and functional chromosome • The chromosomes are pulled toward opposite poles. Anaphase is complete when a complete set of chromosomes reaches each pole.

35. 4. Telophase: The final stage of mitosis, chromosomes uncoil into chomatin threads A nuclear envelope forms around each set of chromosomes, nucleoli appear • Daughter nuclei form • Nuclear envelopes arise • Chromatin becomes less coiled • Two new nuclei complete mitosis

36. Structure of a replicatedchromosome

37. Counting chromosomes and chromatids n = haploid number of chromosomes Example: the humans have 23 different chromosomes (n=23). Diploid cells have 2n chromosome #. Human diploid cells, have 46 chromosomes (2n=46). c = number of chromatids in unreplicated (G1) haploid state.

38. Replication of achromosome during mitosis

39. CONTROLS ON DIVISION • Frequency of mitosis varies between species or even with location within an organism…skin cell versus nerve cells for example, but under similar conditions the length of the cell cycle is constant for a particular type of cell. •  The rate and frequency of mitosis in a multicelluar organism must be controlled… •  The cell requires a protein called maturation promoting factor (MPF). Scientists are still learning how MPF works and controls the cell mitosis.

40.  Read about the effects of Colchicine and the condition of polypoidy  When mitosis occurs each daughter cell receives exactly the same number and kind of chromosomes as the parent  When a haploid cell undergoes mitosis, two haploid cells are produced.

41. The End