Explain the following:

1. Explain the following: "It is not a simple life to be a single cell, although I have no right to say so, having been a single cell so long ago myself that I have no memory at all of that stage of my life." �Lewis Thomas (1913�1993) author, biologist, physician

2. Cell Cycle

3. The Cell Cycle A period of growth, DNA replication and cell division that MOST cells go through Examples of cells that don�t: nerve, brain and muscle Examples of cells that do: blood, intestinal and skin Blood cells-2.4 million per second Cell Cycle is divided into 3 phases Interphase Mitosis Cytokinesis

4. A typical animal cell cycle lasts roughly 24 hours, but depending on the type of cell, it can vary in length from less than 8 hours to more than a year. Most of the variability occurs in G1. This cycle begins when the cell is produced by mitosis and runs until the cell undergoes its own mitosis and splits in two.. As you can see, mitosis only occupies a fraction of the cycle. The rest of the time-phases G1 through G2�is known as interphase. http://publications.nigms.nih.gov/insidethecell/chapter4.html#10

5. The Cycling Cell Scientists used to think of interphase as a resting phase during which not much happened, but they now know that this is far from the truth. It is during interphase that chromosomes�the genetic material�are copied and cells typically double in size. While this is happening, cells continue to do their jobs: Your heart muscle cells contract and pump blood, your intestinal cells absorb the food you eat, your thyroid gland cells churn out hormones, and so on. In contrast, most of these activities cease during mitosis while the cell focuses on dividing. But as you have probably figured out, not all cells in an organ undergo mitosis at the same time. While one cell divides, its neighbors work to keep your body functioning. http://publications.nigms.nih.gov/insidethecell/chapter4.html#10

6. INTERPHASE Interphase Longest phase of the cell cycle Consists of 3 distinct periods

7. G1 phase Proteins are produced, organelles increase (multiply) Cells grow during this phase, increase in size Cells acquire ATP (energy) for later use

8. S phase DNA synthesis (DNA is replicated)

9. G2 phase Changes in cytoskeleton to prepare cell for mitosis Cell undergoes more growth Cell acquires more energy (ATP) http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_cell_cycle_works.html

10. Nucleolus is present Individual chromosomes are NOT visible (DNA is known as chromatin) Nuclear membrane is present

11. Interphase

12. Mitosis Nuclear division, it is the process of forming identical daughter cells by replicating and dividing the original chromosomes, in effect making a cellular Xerox copy. http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html

13. Prophase: 1st stage of mitosis Chromatin forms chromosomes (chromosomes become visible) Centrioles separate, start to move to opposite ends Spindle fibers form Nuclear envelope (membrane) breaks down Spindle fibers attach to centromeres

14. Chromatids Referred to as �sister� chromatids

15. Prophase

16. Metaphase: 2nd stage of mitosis Chromosomes move to center of the cell and line up in the middle of cell Site where chromosomes gather is called the metaphase plate

17. Metaphase

18. Anaphase: 3rd stage of mitosis Shortest stage of mitosis Spindle fibers pull apart chromatids Chromatids move to opposite ends of the cell

19. Anaphase

20. Telophase: 4th stage of mitosis End of mitosis (terminal stage) Spindle fibers (disassemble) break apart Nuclear envelope re-forms around chromosomes Chromosomes begin to break apart Two identical nuclei exist in the cell Nucleolus starts to re-form

21. Telophase

22. CYTOKINESIS Division of cytoplasm following mitosis Results in two daughter cells Animal cells? Plant cells?