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Cell Reproduction

Cell Reproduction. Honors Zoology. Reasons cells divide. Growth and development zygote to adult Replace old cells – lining of digestive tract and skin Repair damaged tissue – heal injuries Reproduction – make offspring GRRR!. 1 cell to 90 trillion. Most animals start out as a zygote

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Cell Reproduction

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  1. Cell Reproduction Honors Zoology

  2. Reasons cells divide • Growth and development zygote to adult • Replace old cells – lining of digestive tract and skin • Repair damaged tissue – heal injuries • Reproduction – make offspring • GRRR!

  3. 1 cell to 90 trillion • Most animals start out as a zygote • A zygote is formed by the union of an egg and a sperm.

  4. Mitosis • The zygote divides to form genetically identical daughter cells. • They divide to form more genetically identical cells.

  5. The Process of Cell Replication Interphase – 3 phases - DNA is called chromatin in interphase G1- Most of the life of the cell. - When they do their ‘work’ S - Time when conditions are right and the signal comes for DNA synthesis to occur. G2 – Organelles reproduce in preparation for Mitosis

  6. DNA Replication • During S phase of interphase a set of enzymes separate the DNA double helix and allow each side to serve as the template for synthesis of a new complementary strand of DNA. • The old molecule separates in half, gets new nucleotides paired with it to produce new DNA molecules that are ½ old and ½ new.

  7. How it Works

  8. The Good News – You do not have to memorize all of that!What to know… • DNA has 2 strands with complementary nucleotides. • Adenine pairs with Thymine and Guanine pairs with Cytosine. • Each strand is replicated in opposite directions. • DNA Polymerase is the enzyme that places the nucleotides and catalyzes their bonds.

  9. What to know continued… • There are several other enzymes involved that unzip and untwist the original strand, hold it open, place RNA primers, hook/repair broken nucleotide bonds, keep it from twisting too tight, and replace the ending segments. • Actually, just know that DNA Polymerase acts in concert with several other enzymes. • The replicated strands remain attached at the centromere – as chromatids

  10. Prophase • After DNA is replicated and repaired, it begins to coil into chromosomes. • They consists of 2 identical copies of the DNA called chromatids. • The chromatids are held together at the centromere which has a protein called the kinetochore. • The kinetochore attaches to spindle fibers during mitosis.

  11. All wrapped up and let’s dance! • DNA is not available for transcription during this time. • While the chromosomes were wrapping up, spindle fibers were growing out of the 2 centrosomes, which usually contain centriolesin animals.

  12. Getting attached and dragged to the dance floor – line dance! • As spindle fibers form the nuclear membrane breaks apart and beads up to be divided between the daughter cells. • The spindle fibers attach to the kinetochore and the chromosome moves back and forth until it settles in the middle on the metaphase plate.

  13. Metaphase • When the Chromosomes are lined up in the middle.

  14. Anaphase • The chromatids separate at the centromere. • The chromatids move down the spindle fibers in opposite directions toward the centrosomes. • The spindle fibers without chromatids push the centrosomes apart making the cell oval shaped.

  15. Telophase • The opposite of prophase. • The chromatids – now chromosomes uncoil into chromatin. • The nuclear membrane reforms. • Spindle fibers disappear.

  16. Cytokinesis – division of the cytoplasm • A cleavage furrow forms where the metaphase plate was. A ring of actin fibers circles the cell and interacts with other proteins to cinch the cell in half. • The infolded edges of the membrane meet and fuse.

  17. The daughter cells • Are genetically identical. • They are clones. • If the cells separate when a zygote under goes mitosis, they are identical twins.

  18. Control • The cycle of cell division and growth is controlled by the rise and fall of protein in the cell, especially cyclin. • Cyclinworks with other proteins called cdk’s to initiate cell division.

  19. Programmed Cell Death • Called apoptosis • Necessary for normal growth and development. Without it you would hae webbed fingers and a tail!

  20. Now… • Use the pop beads to model mitosis for 2 chromosomes – red and yellow. • Your other supplies include yarn, string, beads, magnetic pieces, and two sheets of paper.

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