Cell Division Ch. 10 Why do cells divide? (1) Exchanging materials The larger a cell becomes, the harder it is to get enough materials and waste across the cell membrane. Why do cells divide? (2) DNA Overload Larger cells place more demands on their DNA. Why do cells divide? (3) Surface Area : Volume Ratio As the length of a cell increases, the volume increases much more rapidly than surface area. The Cell Cycle Interphase (period in-between division) – G1 (growth) – S (DNA replication) – G2 (prepare for mitosis) M phase (division) – Mitosis (division of the nucleus) – Cytokinesis (division of the cytoplasm) Most of the time the cell is in interphase!!! Mitosis Mitosis is the division of the nucleus. There are 4 stages of mitosis: – Prophase – Metaphase – Anaphase – Telephase Prophase Everything sets up for mitosis. First and longest stage of mitosis. The chromatin condenses into chromosomes. The centrioles separate and form a spindle of microtubules. The nuclear membrane breaks down. Metaphase Metaphase is the 2nd phase of mitosis. Chromosomes line up on the spindle in the MIDDLE of the cell. May last only a few minutes. Anaphase Anaphase is the 3rd phase of mitosis. Chromosomes are pulled APART to opposite ends of the cell. Begins as soon as the chromosomes begin separating and ends as soon as the chromosomes stop moving. Telophase Last phase of mitosis. Chromosomes disperse and tangle. The nuclear envelope forms around the chromosomes. The spindle breaks down. The nucleolus becomes visible. Cytokinesis The division of the cytoplasm. Occurs at the same time as telephase. The cytoplasm can be divided 2 ways: – Animal cells pinch off into 2 cells. – Plant cells form a cell plate (which is the beginning of the cell wall) Final Product The final product of mitosis and cytokinesis is: –2 genetically identical daughter cells Controls of Cell Growth When cells come into contact with other cells, they stop growing. Cyclins are proteins that regulate the timing of the cell cycle. Cancer Cancer is a disorder where the cell has uncontrolled growth. Cancer cells do NOT respond to regulators. This causes the cells to form masses called tumors, which can damage surrounding tissues.