1. The Cell Cycle and Mitosis: “You Complete Me” A process where one parent cell gives rise to two daughter cells- exact replicas of the original cell.

2. The Cell Cycle The process of the cell that results in two new cells is called cellular Mitosis Why do we need cells to reproduce? Purpose: to replenish dead or dying cells, to allow an organism to grow and develop

3. Interphase This is the phase of the cell prior to Mitosis. It may not look like much is going on here, but there is a lot of activity because the cell must prepare for Mitosis: protein synthesis, DNA replication, replication of other cellular structures too. The cell grows to its full size and copies important structures Special structures called centrioles are formed Onion root tip (on left side), whitefish (on right side)

4. Mitosis Mitosis occurs in order for organisms to grow and develop. In order to replenish dead or dying cells such as skin cells, cells in the digestive tract and in the fertilized egg. There are 4 main phases: Prophase, Metaphase, Anaphase, Telophase. Cytokinesis (division of the cytoplasm) follows and one cell becomes two.

5. Mitosis: Prophase Major processes during this phase: Chromatin condenses and form visible bodies called chromosomes (DNA was replicated in S phase) Nuclear envelope breaks down Onion root tip (top photo), whitefish (bottom photo)

6. Mitosis: Chromosomes When the chromatin condenses, it forms two Chromatids, joined by a Centromere. These are coiled up chromatin fibers formerly in the nucleus, which contain genetic info

7. Mitosis: Metaphase Chromosomes attached to spindle fibers line up in the middle (the equator) of the cell Spindle fibers attach to the centromeres and other places along the chromosome Onion root tip (top photo), whitefish (bottom photo)

8. Mitosis: Anaphase The last bit of DNA at the centromere replicates to allow the the centromere to split The sister chromatids separate and are pulled to opposite sides of the cell The cell stretches to accommodate this new material Onion root tip (top photo), whitefish (bottom photo)

9. Mitosis: Telophase Chromosomes now uncoil Nuclear envelope reappears and surrounds the chromosomes Onion root tip (top photo), whitefish (bottom photo)

10. Mitosis: Cytokinesis Cytokinesis The cytoplasm and all its contents are divided between the 2 daughter cells (cytoplasmic division) The red arrow points at the newly developing plasma (cell) membrane that creates the 2 new daughter cells A cell plate is present in plant cells because the cell wall is too rigid to split The 2 daughter cells are exact replicas of the original parent cell – they are clones and have the exact same genetic make-up as the parent cell.

11. Can you identify these stages? Answers: A. TelophaseB. ProphaseC. CytokinesisD. Metaphase A B C D

12. DNA Structure and Replication First discovered by Rosalind Franklin in 1952 using x- rays, later further studied by Watson and Crick DNA is like a ladder Double strands are held together by Nitrogen bonds

13. DNA Structure and Replication There are four types of Nitrogen bonds: Adenine, Thymine, Guanine, and Cytosine When it comes time for the cell to divide, the DNA unzips like a zipper, and reproduces It is then bonded with free floating nitrogen bases in the cell Once the DNA is replicated, the two new strands are exactly the same as the old