Section 8-2 The Cell Cycle & Cell Division

1. Section 8-2 The Cell Cycle & Cell Division

2. The Cell Cycle The Cell cycle is a series of stages that a cell goes through in which it grows, performs basic functions and divides to create new material or replace damaged tissue. There are a total of 44 turns of the cell cycle from the formation of the zygoteuntil the end of gestation when a baby is born!

3. The Cell Cycle The Cell cycle has three main stages: • Interphase – the time between divisions = 90% of the time. • Mitosis – division of the nucleus both of these are • Cytokinesis – division of the cytoplasm = 10% of the time.

4. Interphase Phase I: The first part of interphase is called G1. This stands for Gap 1 which is the time between cell division and DNA replication. During this time the cell doubles in size and many organelles are made. The DNA is in the chromatin form and not yet copied.

5. Interphase There is a checkpoint that cells have to pass though after this stage. Some cells never pass it and enter a G0stage where they never divide. An example is nerve cells. If a cell is not supposed to pass through and does, cancer could result from the overgrowth of tissue.

6. Interphase Phase 2: The second part of interphase is called the S phase. This stands for synthesis which involves DNA replication. The DNA is copied but still is in the chromatin form. There is another checkpoint here where the proofreading and repair enzymes check for errors in the replication process.

7. Interphase Phase 3: The final part of interphase is called the G2 phase. This stands for Gap 2 and is the time between replication and cell division. The cell grows more and the organelles and centrioles are replicated. The DNA is still in the chromatin form.

8. Mitosis The first phase of mitosis is Prophase (Prepare). The centriolesmove to opposite poles of the cell. The nuclear membrane breaks down. The DNA condenses into replicated chromosomes.

9. Mitosis The second phase of mitosis is Metaphase (Middle). The centriolesproduce spindle fibers that span the cell. Chromosomes attach to the spindle at the centromeres and line up in the middle of the cell in a single-file line.

10. Mitosis The third phase of mitosis is Anaphase (Apart). The centrioles retract the spindle fibers to each end of the cell. Chromosomes split into chromatids that each move to opposite ends. One copy of each gene is contained in each of the chromatids that split.

11. Mitosis The fourth phase of mitosis is Telophase (Two). The spindle dissolves and the nuclear membrane reforms around the unreplicatedchromosomes that now exist in each new cell. Proteins pinch in the cytoplasm to begin to divide the cell in half.

12. Cytokinesis Cytokinesis involves the splitting of the cell into two daughter cells. The DNA uncoils into the chromatin form again. There is another checkpoint here to insure that cells reenter interphase. Some cells like red blood cells rapidly go through the cell cycle because their lifespan is so short.