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Unit-III Mitosis

Unit-III Mitosis. Cell Replication. Cell Replication. During cell division two events occur- The replicated genetic information of a cell is equally distributed in mitosis. After mitosis, the cytoplasm of the cell also divided into two new cells.

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Unit-III Mitosis

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  1. Unit-III Mitosis Cell Replication

  2. Cell Replication • During cell division two events occur- • The replicated genetic information of a cell is equally distributed in mitosis. • After mitosis, the cytoplasm of the cell also divided into two new cells. • The division of cell’s cytoplasm is called CYTOKINESIS- cell spliting.

  3. Mitosis Phases • PROPHASE • METAPHASE • ANAPHASE • TELOPHASE

  4. PROPHASE-Early Prophase • Chromosomes appear as thin, tangled threads and the nucleus and nucleolus are present. Centrioles begin to separate and and move to opposite poles of the cell. • A series of fibers, known as the spindle will shortly begin to form.

  5. Early and late Prophase

  6. Late Prophase- • The chromosomes appear as two chromatids connected at a centromere. • The centrioles have moved farther apart, the spindle is produced, and the chromosomes are attached to the spindle fibres. • Nuclear membrane have disassembled.

  7. Prophase-Key Events • Chromosomes condensed. • Spindle and spindle fiber formation. • Nuclear membrane disassembles. • Nucleolus disappears.

  8. Prophase- • Prophase is the first stage of mitosis. • Formation of spindle and spindle fibers. • Spindle fiber is a structure, made of microtubules , that span the cells from one side to the other. • In animal cells, the spindle forms between the centrioles. • In plant cells, the spindle forms with out centrioles.

  9. METAPHASE-Key Events • 2nd stage of the Mitosis. • Chromosomes align at the equatorial plane of the cell. • The equatorial plane is the region in the middle of the cell. • Each chromosome still consists of 2 chromatids. • When viewed from from the edge the chromosome appears to be lined up. • When viewed from another angle, they appeared to be spread apart.

  10. ANAPHASE-Key events • 3rd stage of Mitosis. • Sister chromatids move towards opposite ends of the cell. • The chromatids also called daughter chromosomes, are separating and moving towards the poles.

  11. TELOPHASE-Key Events • 4th stage of the Mitosis. • The spindle disassembles. • Nucleolus and the nuclear membrane reforms. • Chromosomes uncoil back to chromatin. • With the separation of genetic material into two nuclei, mitosis is complete. • Cell finishes Mitosis.

  12. CYTOKINESIS • During cytokinesis the cell content are split between the two daughter cells. • In animal cell- cytokinesis results from the formation of cleavage furrow. • The cleavage furrow is an indentation of the plasma membrane that pinches in towards the center of the cell and splitting the cytoplasm into two.

  13. Cytokinesis- • In plant cells, a cell plate is formed at the center of the cell and grows out to the plasma membranes. • The cell wall is then formed between the newly formed cells. • The completion of Mitosis and cytokinesis marks the end of the one round of cell division. • Each of newly formed daughter cells then starts the cell’s cycle over by entering interphase at G1.

  14. Summary- Mitosis is much more than splitting the cytoplasm of the cell into two parts. It ensures that the genetic material is split appropriately between daughter cells.By dividing the genetic information as sister chromatids, the daughter cells inherit the same genetic information that was present in the parent cell.

  15. Concept Review- • Define Mitosis. • Name the 4 stages of mitosis and describe what occurs in each stage. • During which stage of a cell’s cycle does DNA replication occur? • At what stage of mitosis does a chromosome become visible? • List five differences between an interphase cell and a cell in mitosis. • Define the term Cytokinesis. • What are the differences between plant mitosis and animal mitosis? • What is the difference between cytokinesis in plant and animals?

  16. Controlling Mitosis- • The cell division process is regulated so that it does not interfere with the activities of other cells or of the whole organism. • CHECKPOINTS are times during the cell cycle when cells determine if they are prepared to move forward with cell division. • At these checkpoints, cells use proteins to evaluate their genetic health, their location in the body, and a need for more cells.

  17. Poor genetic health, the wrong location and the crowded conditions are typically interpreted as signal sto wait. • Good genetic health, the correct location, and uncrowded conditions are interpreted as signals to proceed with cell division.

  18. PROTO-ONCOGENES code for proteins that encourages cell division. • TUMOR-SUPPRESSOR GENES code for proteins that discourages cell division. • A healthy cell receives signals from both groups. • The balance of information provided by these two groups of proteins allows for controlled cell division.

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