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Cell Division “All cells come from pre-existing cells.” HOW? PREVIEW VIDEO MITOSIS Mitosis – division of somatic cells. In higher organisms, mitosis only occurs in somatic cells such as liver, kidney, and skin. Mitosis does not occur in sex cells (sperm and egg). Mitosis WHY MITOSIS? 1. Grow. 2. Repair and replace. WHAT ARE CHROMOSOMES? Chromosomes come in linked pairs called chromatids. These are held together at a centromere. CHROMATIDS CENTROMERE What does mitosis look like? Video of mitosis Understanding mitosis requires an understanding of the stages of mitosis. What are the stages of mitosis? INTERPHASE A. Normal cell function. B. DNA is copied. Plant and animal cells in interphase. Interphase Chromatid Chromatid Centromere DNA Synthesis Chromosome before DNA Synthesis Chromosome after DNA Synthesis PROPHASE A. Nuclear membrane dissolves. Easier to move when cells divide! B. Chromosomes condense. CHROMATIN condenses into CHROMOSOMES Prophase C. SPINDLE FIBERS attach to the CENTROMERE of each chromosome. Prophase Plant and animal cells in prophase. Metaphase Chromosomes line up in middle of the cell. Plant and animal cells in metaphase. Anaphase A. Spindle fibers pull chromatids apart. B. Chromatids move to opposite ends. Plant and animal cells in Anaphase. Telophase and Cytokinesis A. Chromosomes reach opposite ends. B. Nuclear membrane is remade. C. Cytokinesis – cell membrane pinches in to form two new cells. In plants, cell wall forms between both cells. Telephase and Cytokinesis Plant and animal cells in Telophase. Cytokinesis A good way of remembering the stages of mitosis is: I Prefer Mangoes After Tea OVERALL GOAL OF MITOSIS Divide one cell into two cells. Keep the chromosome number the same. Mitosis ANIMATION OF PLANT CELL MITOSIS – click on “Plant Cell Mitosis” on left MITOSIS IN NEWT LUNG CELLS – click on “Live Animal Mitosis” on left MITOSIS VIDEO QUIZ PLANT CELL INTERPHASE PLANT CELL PROPHASE PLANT CELL METAPHASE PLANT CELL ANAPHASE PLANT CELL TELOPHASE ANIMAL CELL INTERPHASE ANIMAL CELL PROPHASE ANIMAL CELL METAPHASE ANIMAL CELL ANAPHASE ANIMAL CELL TELOPHASE WHEN DOES MITOSIS OCCUR? G1 – normal cell functions S – DNA is copied G2 – normal cell functions Cell Cycle Movie In otherwords: Cells do a lot more than just reproduce! HOW LONG DOES MITOSIS TAKE? Bacteria – Every 20 minutes! Human Kidney cells – 24 hours Human Nerve cells – Don’t divide after birth Onion Root Tip - 720 minutes (12 hours) HOW LONG DOES MITOSIS TAKE? When does mitosis occur? All through life! When during life does mitosis occur the fastest? Before birth. # of cells in a phase 720 = Total time spent * Total # of cells in that phase Cancer – When Cell Cycle Doesn’t Stop Cell Cycle Animation Cell Cycle doesn’t always keep going Checkpoints to make sure cycle is done correctly. Checkpoint Checkpoint Checkpoint What happens during a checkpoint? Checkpoint #1 – During G1, Cdk checks if cell has grown enough. Checkpoint #2 – End of G2, p27 checks if chromosomes have been copied. Checkpoint #3 – During metaphase, p53 checks if chromosomes are lined up in middle of cell. Mutated p53 is most frequent cause of cancer. APOPTOSIS If cell is too damaged, apoptosis or “programmed cell death” occurs. What organelle might be involved in this process? LYSOSOME APOPTOSIS When else during life does “programmed cell death” occur? Prior to birth CANCER If cell cycle isn’t performed correctly, cells become cancerous. CANCER VIDEO
