C ELL C YCLE Dr. Brasington

S OMATIC CELL DIVISION The process of a cell dividing into 2 identical daughter cells. Occurs when cells reach a certain age A means of body growth, replacing older cells, and repairing injured parts of the body. 3 stages: interphase, mitosis, and cytokinesis.

I NTERPHASE Cells spend most of their time in interphase. Subdivided into G1, S, G2.  G0? G1: Cell grows larger S: Chromosomes are duplicated and the amount of DNA doubles. G2: More growth and cell prepares for mitosis. Mitosis: The division of the nucleus to produce 2 diploid nuclei. -Occurs at the END of interphase.

P HASES OF M ITOSIS Prophase Metaphase Anaphase Telophase

P ROPHASE The nuclear membrane disappears. The spindle apparatus begins to form. The chromosomes (comprised of 2 sister chromatids)condense.

P ROPHASE

M ETAPHASE Chromosomes line up at the equator at the metaphase plate. Centrioles align at opposite poles. Microtubules that make up the spindle fibers extend from the poles to the center of the cell. Chromosomes move randomly until they attach at their kinetochores to polar fibers from both sides of their centromeres. Kinetochores: Protein structure where spindle fibers attach to pull sister chromatids apart.

M ETAPHASE

A NAPHASE The paired centromeres begin to move apart. Once the paired sister chromatids separate from one another, each is considered a “full” chromosome “daughter chromosomes”. Through the spindle apparatus, the daughter chromosomes move to the poles at opposite ends of the cell. The 2 poles of the cell also begin to move apart. At the end of anaphase, each pole has a complete compilation of chromosomes.

A NAPHASE

T ELOPHASE Nuclei begin to form at opposite poles. Nuclear envelopes are formed. Nucleoli reappear. Chromatin fibers of the chromosomes uncoil. Spindle fibers and centrioles disappear. Cytokinesis. Completion of the cycle marks beginning of life cycle for the 2 daughters. Life cycle ends when the 2 daughters divide again.

T ELOPHASE

T HE E ND