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The Cell Cycle

The Cell Cycle. Cell division. Is the process by which cells divide into 2 daughter cells Cells do this to prevent from becoming to large Recall…why don’t cells grow to be large?. Preparation before division. If a cell didn’t prepare before it divided, would it be able to survive? NO

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The Cell Cycle

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  1. The Cell Cycle

  2. Cell division • Is the process by which cells divide into 2 daughter cells • Cells do this to prevent from becoming to large • Recall…why don’t cells grow to be large?

  3. Preparation before division • If a cell didn’t prepare before it divided, would it be able to survive? • NO • Before a cell can divide it MUST: • 1. Make a copy of the DNA, this way each cell can have a complete set • 2. Have extra of most organelles so that each of the daughter cells will be functional

  4. DNA • Usually is stored in the form of chromatin • Chromatin carries all of an organisms genetic information • Are unwound, non-visible strands of DNA • Condenses to chromosomes/ chromatids before the cell divides • Chromatids and chromosomes are tightly wound up DNA that is visible

  5. Sister Chromatids • Before a cell divides, each chromosome is copied and when they condense into chromatids, there are 2 identical copies • These are called Sister Chromatids • The sister chromatids are connected together by a centromere

  6. The cell cycle • Is a series of events that a cell undergoes as it grows and divides • The four main steps are • 1. Growing • 2. Preparing for Dividing • 3. Dividing into 2 daughter cells • 4. Starting at step 1 again

  7. The cell cycle • The 2 major phases of the cell cycle are • 1. Interphase—this is the period of growth that a cell undergoes, the time when it is NOT dividing • It also prepares to divide during this time by making a copy of the DNA • 2. Mitosis—this is the time when a cell is actively dividing • It consists of 4 steps, plus cytokinesis

  8. Mitosis Step 1 –Prophase • The nuclear envelope breaks down • Chromatin condenses into the chromosomes. • Centrioles separate to opposite ends of the cell. • Mitotic spindle begins to form.

  9. Mitosis Step 2 –Metaphase • Chromosomes line up at the equator to the cell • The spindle fibers connect to the centromeres of each sister chromatid

  10. Mitosis Step 3—Anaphase • Centromeres joining the sister chromatids together split apart • The chromatids are pulled to opposite sides of the cell

  11. Mitosis Step 4 –Telophase • Chromosomes begin to decondense • The nuclear envelope reforms (this time there is 2, one on each side) • The spindle breaks apart

  12. Cytokinesis • Means to divide the cell, so it is after mitosis and the cell splits into 2 independent cells • In animals, the cells suck in and then “pinch off” • In plants, a cell plate is formed that gradually turns into a new cell wall

  13. Cyclins • Are a class of hormones that control the cells cycle • They decide when cells are to divide and when the are NOT to divide • Cancer is considered UNCONTROLLED cell division and can lead to serious problems

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