1 UNIT 2 PART 2: CELL DIVISION All cells come from other cells. Each round of cell growth and division is called the cell cycle. For unicellular organisms, this is reproduction because it results in a new individual.

2 In a cell with a nucleus two processes take place: Mitosis –The division of the nucleus –It has four stages Prophase Metaphase Anaphase Telophase Cytokinesis –The division of the cytoplasm –Forms two separate cells –These cells are genetically identical Before mitosis the cell must grow and prepare. This happens during Interphase, where the cell spends most of its time.

3 Interphase From the end of one division to the beginning of the next: G1, S, and G2. This is when the cell grows, makes more organelles and proteins, and replicates the chromosomes so they become doubled. Centrioles in animal cells also replicate. During Interphase, the chromosomes are uncoiled, not visible, and called chromatin.

4 Prophase Doubled chromosomes become visible. –Each strand is called a chromatid. –The chromatids are connected by a centromere. Centrioles move to the poles. Microtubules form asters and the spindle apparatus that stretches from pole to pole. Nuclear membrane and nucleolus disappear. chromatids

5 Metaphase Centromeres, which are connected to spindle fibers, line up in the middle of the cell on the metaphase, or equatorial, plane. By the end of metaphase the centromeres divide and the chromatids become separate chromosomes.

6 Anaphase The chromosomes are pulled to opposite poles by the spindle fibers so that there is one complete set at each end of the cell.

7 Telophase The chromosomes reach the poles and will uncoil again into chromatin. The spindles and asters disappear. A nuclear membrane forms around each set of chromosomes forming two daughter nuclei. Nucleoli reappear.

8 Cytokinesis: The formation of two separate identical cells In animal cells the cell membrane pinches in until opposite sides touch and two new cells are formed. In plant cells a cell plate forms between the two daughter nuclei and forms a new cell wall.

9 MITOSIS REVIEW - IPMAT Interphase – chromatin and replication of DNA Prophase – chromosomes visible Metaphase – lined up in the middle Anaphase – chromosomes move Telophase – two new nuclei form

10 Mitosis Animation

11 Some Mitosis Facts The two daughter cells made from mitosis are identical to each other and the parent cell. Mitosis happens most often in least specialized cells like early embryos. Specialized cells like xylem, muscle, and nerve cells rarely, if ever, divide. Places of growth like root tips, bone marrow, and skin have cells that divide rapidly. A protein called cyclin regulates the cell cycle.