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Transcript
The Process of Cell Division The Cell Cycle The cell cycle consists of three stages: – Interphase – stage before the cell divides – Mitosis - the nucleus divides – Cytokinesis - the whole cell divides Stage One - Interphase Most of the life of a cell is spent in a period of growth and development called interphase. Chromosomes Chromosomes are structures in the nucleus that contain DNA. During interphase, you can’t see chromosomes but they are actively replicating themselves. Each chromosome is held together in the middle by a centromere. Once the chromosomes have doubled, the cell is ready to begin dividing. centromere Stage Two - Mitosis • The cell that is dividing is called the parent cell. • Mitosis is the process in which a cell nucleus divides into two new nuclei. Each new nucleus has the same number of chromosomes as the parent cell. The Four Steps of Mitosis Mitosis is described as a series of four steps. 1. 2. 3. 4. Prophase Metaphase Anaphase Telophase Step 1 - Prophase During prophase, the chromosomes become visible. The membrane around the nucleus disappears. Spindle fibers begin to stretch across the cell. whitefish mitosis Step 2 - Metaphase In metaphase, the chromosomes line up in the middle of the cell. Each centromere attaches itself to a spindle fiber. Step 3 - Anaphase In anaphase the centromere divides and the two pieces (strands) of the chromosome separate. The separate strands begin to move away from each other toward the opposite sides of the cell. Step 4 - Telophase In telophase, spindle fibers disappear. The chromosomes become harder to see. A nuclear membrane forms around each set of chromosomes. whitefish mitosis Stage Three – Cytokinesis Animal Cells In animal cells the cytoplasm pinches in to form the new cells. The new cells then begin a period of growth and are in interphase. Cytokinesis - Plant Cells Plant cells have rigid cell walls so they can’t pinch apart like animal cells do. Instead, a cell plate forms between the two new nuclei. New cell walls form along the cell plate. New cell walls Onion root tip mitosis 46 Chromosomes Most of the cells in your body have 46 chromosomes. Each new cell produced by mitosis will also have 46 chromosomes. Humans have 46 chromosomes Human Chromosomes Chromosome Numbers Fruit fly cells have eight chromosomes. New fruit fly cells produced by mitosis will each have eight chromosomes. Carrot cells have eighteen chromosomes before and after mitosis. Mitosis in Onion Cells interphase prophase metaphase anaphase telophase Can You Find Cells in the Different Phases of Mitosis? Hope You Enjoyed the Show!