ELL DIVISION with all needed content.pptx

With all notes

1. CELL DIVISION and THE CELL CYCE PRESENTED BY: RWAPEMBE STEPHEN 2022/U/MMU/BNSD/003 MUHUMUZA B. FRANCIS 2022/U/MMU/BNSD/001 WAMUTIBI ANDREW BOSCO 2022/U/MMU/BNSD/009

2. CELL DIVISION It’s the process by which a cell divides to form two new cells Three types of cell division or cell reproduction in organism Prokaryotes (bacteria) Binary fission Divides forming two new identical cells

3. Eukaryotes Mitosis Cell or organism growth Replacement or repair of damaged cells Meiosis formation of sex cells, or gametes

4. WHY DO CELLS DIVIDE? Cells divide for growth, development, repair of worn-out tissues and reproduction To facilitate the exchange of materials To control DNA overloading

5. PROKARYOTIC CELL DIVISION Binary Fission Three (3) major steps; DNA Replication DNA is copied resulting into two identical chromosomes Chromosome Segregation Chromosomes separate and move towards ends (poles) of cell Cytokinesis (Separation) Cytoplasm divides forming two (2) cells Each new daughter cell is Genetically Identical to parent cell

6. Prokaryotic Cell Division

7. EUKARYOTIC CELL DIVISION Cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent cell MITOSIS Two (2) main steps: Mitosis Fours steps; [Prophase>Metaphase>Anaphase>Telophase] Cytokinesis Cytoplasm divides forming two new daughter cells Each daughter cell is Genetically Identical to parent cell

8. Eukaryotic Cell Division Cont. Cell division that results in four daughter cells MEIOSIS Two (2) major steps: Mitosis Fours steps; [Prophase>Metaphase>Anaphase>Telophase] Cytokinesis Cytoplasm divides forming two new daughter cells Each daughter cell is NOT Genetically Identical to parent cell

9. CELL CYCLE

10. THE CELL CYCLE The sequence of events from the time a cell first arises as a result of cell division until the time when that cell itself divides. Arise – Divide This consist of periods of; Growth and Development DNA Replication Preparation For Division Cell Division Cell after division begins a new cycle

11. The Cell Cycle Consist of two(2) main periods; Interphase Mitotic Phase M phase G 2 phase S phase G 1 phase

12. CELL CYCLE - Interphase Interphase: period of growth and DNA replication between cell divisions Three (3) phases: G 1 Phase Cell increases in size S Phase Replication of DNA Two sister strands of DNA called chromatids are produced G 2 Phase Organelles double New cytoplasm forms All other structures needed for mitosis form Centrioles Nuclear membrane Nucleolus Chromosomes

13. CELL CYCLE – Mitotic Phase Mitotic phase is the stage when a cell divides Mitosis – the division of a single nucleus into two genetically identical daughter nuclei This division involves two(2) processes; Division of the nucleus Separation of the cytoplasm and the new nuclei into daughter cells

14. Mitotic Phase Divided into two (2) mitotic phases 1 st MP contain four stages (P-MAT ) Prophase, metaphase, anaphase and telophase 2 nd MP is cytokinesis

15. Prophase Metaphase Anaphase Telophase P-MAT Interphase 1 2 3 4 Cytokinesis Mitosis

16. Interphase: the cell grows and the nuclear DNA is duplicated . Centrioles Nuclear membrane Nucleolus Chromatids

17. Early Prophase: Chromatids condense becoming chromosomes Nucleolus disappears( The nucleolus is considered as the brain of the nucleus, covering nearly 25% volume of the nucleus. Primarily, it takes part in the production of subunits that unites to form ribosomes) Centrioles separate and start moving to opposite ends of the cell Spindle begins to form Chromatids connected by a centromere . Centrioles Spindle made of microtubules

18. Late Prophase: The nuclear membrane fragments and the microtubules invade the nuclear area Centrioles have moved to the opposite poles The spindle is completely formed centrioles Microtubules form a complete spindle chromatids centrioles

19. Metaphase: In metaphase; The chromosomes are aligned at the metaphase plate Centrioles move at polar ends and projects spindle fibers to connect each chromosome Centriole s Chromosomes Spindle composed of microtubules

20. Anaphase: In anaphase; The paired chromosomes (sister chromatids) separate Separated chromatids move to opposite pole Partial division of cytoplasm begins Chromatids are being pulled to opposite sides of the cell . Shortening of the microtubules

21. Telophase: In telophase; Chromosomes are at the poles Chromosomes uncoil-turn chromatin Nuclear envelops reforms Spindle fiber disappear Nuclear membrane is returning

22. Cells return to interphase Cytokinesis: Occurs at the end of mitosis Animal cells: a cleavage furrow separates the daughter cells Plant cell : a cell plate separates the daughter cells Daughter cells are genetically identical

23. Mitosis Animation

24. CONTROL OF THE CELL CYCLE Regulatory proteins called cyclins control the cell cycle at checkpoints: G1 Checkpoint —decides whether or not cell will divide S Checkpoint —determines if DNA has been properly replicated Mitotic Spindle Checkpoint —ensures chromosomes are aligned at mitotic plate

25. MEOSIS Meiosis is the process in eukaryotic, sexually-reproducing animals that reduces the number of chromosomes in a cell before reproduction.

26. Phases of Meiosis It is the first step in meiosis I, is similar to prophase in mitosis in that the chromosomes condense and move towards the middle of the cell. The nuclear envelope degrades, which allows the microtubules originating from the centrioles on either side of the cell to attach to the kinetochores in the centromeres of each chromosome. Unlike in mitosis, the chromosomes pair with their homologous partner. This can be seen in the red and blue chromosomes that pair together in the diagram. This step does not take place in mitosis. At the end of prophase I and the beginning of metaphase I, homologous chromosomes are primed for crossing-over.

27. Between prophase I and metaphase I, homologous chromosomes can swap parts of themselves that house the same genes. This is called  crossing-over  and is responsible for the other law of genetics, the  law of independent assortment . This law states that traits are inherited independently of each other. For traits on different chromosomes, this is certainly true all of the time.

28. Metaphase 1 In metaphase I of meiosis I, the homologous pairs of chromosomes line up on the metaphase plate, near the center of the cell. This step is referred to as a  reductional division . The homologous chromosomes that contain the two different alleles for each gene are lined up to be separated. As seen in the diagram above, while the chromosomes line up on the metaphase plate with their homologous pair, there is no order upon which side the maternal or paternal chromosomes line up

29. According to the law of segregation, each allele has the same chance of being passed on to offspring. In metaphase I of meiosis, the alleles are separated, allowing for this phenomenon to happen.

30. Anaphase I Much like anaphase of mitosis, the chromosomes are now pulled towards the centrioles at each side of the cell. However, the centrosomes holding the sister chromatids together do not dissolve in anaphase I of meiosis, meaning that only homologous chromosomes are separated, not sister chromatids.

31. Telophase I In telophase I, the chromosomes are pulled completely apart and new nuclear envelopes form. The plasm membrane is separated by  cytokinesis  and two new cells are effectively formed.

32. Phases of Meiosis II Prophase II Prophase II resembles prophase I. The nuclear envelopes disappear and centrioles are formed. Microtubules extend across the cell to connect to the kinetochores of individual chromatids, connected by centromeres. The chromosomes begin to get pulled toward the metaphase plate.

33. Metaphase II Now resembling mitosis, the chromosomes line up with their centromeres on the metaphase plate. One sister chromatid is on each side of the metaphase plate. At this stage, the centromeres are still attached by the protein  cohesin .

34. Anaphase II The sister chromatids separate. They are now called sister chromosomes and are pulled toward the centrioles. This separation marks the final division of the DNA. Unlike the first division, this division is known as an  equational division , because each cell ends up with the same quantity of chromosomes as when the division started, but with no copies.

35. Telophase II As in the previous telophase I, the cell is now divided into two and the chromosomes are on opposite ends of the cell. Cytokinesis or plasma division occurs, and new nuclear envelopes are formed around the chromosomes.

36.       × Meiosis Stages

37. REFERENCE Nabor , Murray W., INTRODUCTION TO BOTANY . Copyright 2004 Pearson Education, Inc., Publilshing as Benjamin Cummings, 1301 Sansome St., San Francisco, CA 94111. www.aw-bc.com CK – 12 https://www.ck12.org/biology/cell-division/lesson/Cell-Division-BIO/ Image Attributions [ Prokaryotic cell division ] Credit: Mariana Ruiz Villarreal ( LadyofHats ) for CK-12 Foundation Source: CK-12 Foundation License: CC BY-NC 3.0