DO NOW: How many chromosomes are in each of the four cells below? Binary Fission in Prokaryotes 1. Chromosome copies 2. Growth 3. Division Cell Cycle Cell Cycle The Life Cycle of a cell Rate of Cell Cycle depends on the cell: - Fast: embryo - Fastest: skin, digestive tract - Don’t divide: muscle (heart) and nerve (brain) Interphase - First stage & longest of cell cycle Nucleus and nucleolus clearly visible Chromosomes not visible. Not part of “Mitosis” G1 = growth and activity S = chromosomes copied G2 = final preparations for cell division G0 = do not copy or divide Cell Division • Stage of the cell cycle when the cell is actually dividing. • 2 stage process: 1. Mitosis – the nucleus divides and each daughter cell is identical to the parent cell 2. Cytokinesis – cytoplasm divides The Four phases of Mitosis PMAT Prophase chromatin condenses (chromosomes are now visible) Chromosomes consist of two sister chromatids nuclear membrane disappears Centrosomes start to move to opposite ends (poles) of cell Spindle fibers begin to form Kinetochore Fibers Polar Fibers Metaphase Spindles are fully formed kinetochore fibers move chromosomes to line up at the center (equator) of the cell Anaphase • Sister chromatids separate and move to opposite poles. • Each chromatid is now considered an individual chromosome Telophase 2 nuclear envelopes reform Chromosomes uncoil into chromatin Spindles disappear Cytokensis cytoplasm is divided in half ANIMAL PLANT Animation of Mitosis 1. Why does the nucleus enlarge during the S phase? 2. If the cell meets all the criteria at each of its checkpoints, it finally enters the M phase. Describe what happens during this final stage of the cell cycle. 3. Do all cells complete the cell cycle or go through it at the same rate?