Cell cycle & Cell division

Review of Cell cycle & Cell division

1. Cell Cycle Cell Division &

2. Why do cells divide? GROWTH REPAIR REPRODUCTION

3. Cell cycle

4. Cell cycle Sequence of self-regulated events that controls cell growth and cell division

5. Cell cycle (contd.) M phase G 2 phase S phase G 1 phase

6. Cell cycle (contd.) Interphase: G 1 Gap between mitosis & DNA replication Gather nutrients Synthesizes RNA & proteins necessary for DNA synthesis and replication

7. Cell cycle (contd.) Interphase: S Period of DNA synthesis Replication of DNA At the beginning of this phase, The chromosome number is (2n) , and T he DNA content is also (2d ) At the end of this phase, The chromosome number remains the same (2n) , and T he DNA content doubles to (4d )

8. Cell cycle (contd.) Interphase: G 2 Gap between DNA replication & next mitosis Growth of cell Reorganization of cellular organelles

9. Cell cycle (contd.) G Leaves the cell cycle

10. Cell cycle (contd.)

11. Cell division MITOSIS MEIOSIS & Equational division Reduction division

12. CHROMATIN CHROMATID CHROMOSOME

13. Mitosis

14. Mitosis Mitosis is a process of c hromosome segregation and nuclear division followed by cell division that produces two daughter cells with the same chromosome number and DNA content as the parent cell

15. Mitosis Mitosis is a process of chromosome segregation and nuclear division followed by cell division that produces two daughter cells with the same chromosome number and DNA content as the parent cell

16. Mitosis (contd.) Prophase Replicated chromosomes condense and become visible T he centrioles separate and migrate to opposite poles of the cell The nucleolus disappears M icrotubules of the mitotic spindle appear between the two centrosomes Microtubules of the developing mitotic spindle attach to the chromosomes

17. Mitosis (contd.) Metaphase The chromosomes are moved to the equatorial plane of the cell .

18. Mitosis (contd.) Anaphase The sister chromatids separate from each other They are slowly pulled at their kinetochores toward opposite spindle poles.

19. Mitosis (contd.) Telophase The two sets of chromosomes are at the spindle poles and begin reverting to their decondensed state. Nuclear envelope begins to reappear around each set of daughter chromosomes. A belt-like contractile ring produce cleavage furrow, containing actin and myosin filaments, develops in the peripheral cytoplasm at the equator of the parent cell. It progresses until the cytoplasm and its organelles are divided in two daughter cells, each with one nucleus.

20. Mitosis (contd.)

21. Meiosis

22. Meiosis Meiosis is a process involving two sequential nuclear divisions followed by cell division that produce gametes c ontaining half the number of chromosomes and half the DNA found in parent cells

23. Meiosis Meiosis is a process involving two sequential nuclear divisions followed by cell division that produce gametes c ontaining half the number of chromosomes and half the DNA found in parent cells

24. Meiosis (contd.) Meiosis I Meiosis II &

25. Meiosis (contd.) Why this reduction is necessary? To maintain a constant number of chromosomes In a given species

26. Meiosis (contd.) Prophase I Double-stranded chromosomes condense , and homologous chromosomes (normally one inherited from the mother and one from the father) are paired at R ecombination of genetic material between the maternal and paternal chromosome pairs may occur.

27. Meiosis (contd.) Leptotene Condensation of chromatin and by the appearance of chromosomes. Zygotene Synapsis , the close association of homologous chromosomes , begins at this stage and continues throughout pachytene . Pachytene Crossingover occurs that involves transposition of DNA strands between two homologous chromosomes. Diplotene Homologous chromosomes begin to separate from each other and appear to be connected by newly formed junctions between chromosomes called chiasmata. Diakinesis The homologous chromosomes condense and shorten to reach their maximum thickness, the nucleolus disappears , and the nuclear envelope disintegrates.

28. Meiosis (contd.) Metaphase I Metaphase I is similar to the metaphase of mitosis except that the paired chromosomes are aligned at the equatorial plate with one member on either side. In late metaphase chiasmata are cleaved and chromosomes are separated.

29. Meiosis (contd.) Anaphase I & Telophase I Anaphase I and telophase I are similar to the same phases in mitosis except that the centromeres do not split. A maternal or paternal member of each homologous pair, now containing exchanged segments, moves to each pole.

30. Meiosis (contd.) Meiosis II After meiosis I, the cells quickly enter meiosis II without passing through an S phase. Meiosis II is an equatorial division and resembles mitosis.

31. Meiosis (contd.)

32. Meiosis (contd.)

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