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Cell Cycle and Mitosis

THE CELL CYCLE
The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell between its formation and the moment it replicates itself. These events can be divided in two main parts: interphase (in between divisions phase grouping G1 phase, S phase, G2 phase), during which the cell is forming and carries on with its normal metabolic functions; the mitotic phase (M mitosis), during which the cell is replicating itself. Thus, cell-division cycle is an essential process by which a single-cell fertilized egg develops into a mature organism and the process by which hair, skin, blood cells, and some internal organs are formed.

1. What is meant by the cell cycle or cell division cycle?

2. In what type of cells --- prokaryotes or eukaryotes --- does the cell cycle occur?

3. Name the 2 main PHASES of the cell cycle.

4. __________ is in between the times when a cell is dividing.

5. What is occurring in a cell during interphase?

6. What is occurring during the mitosis phase?

7. A fertilized cell develops into a ___________ organism during the cell cycle.

8. Name three things that form during the cycle.

INTERPHASE
Interphase is a phase of the cell cycle, defined only by the absence of cell division. During interphase, the cell obtains nutrients, and duplicates (copies) its chromatids (genetic material). The genetic material or chromatids are located in the nucleus of the cell and are made of the molecule DNA. 9. What process NEVER occurs in interphase?

10. Cells obtain ______________ and duplicate or copy their ___________ or genetic material during interphase. 11. Where are chromatids found in a cell?
12. Chromatids are made of a molecule called ___________.
Chromatids are connected by the centromere and have a LONG AND SHORT ARM.

Label the parts of the chromosome including the long and short arms.

1. ___________________

2. ___________________

3. ___________________

4. ___________________
Most eukaryotic cells spend most of their time in interphase. For example, human skin cells, which divide about once a day, spend roughly 22 hours in interphase. About 90 percent of cells are in interphase. Some cells, such as nerve cells, can stay in interphase for decades. There are 3 parts of interphase: G1 (growth 1 in which the cell creates organelles and begins metabolism), S phase (DNA synthesis in which the chromosomes of the cell are copied) and G2 (growth 2 in which the cell grows in preparation for cell division). Find the cell cycle drawing on this worksheet and draw an additional line in red around those parts of the cell cycle diagram that are included in interphase. 13. In what PHASE do most cells spend the majority of their lifetime? 14. How often do human skin cells divide each day?

15. How many hours per day is a human skin cell in interphase? 16. What type of cell may spend decades in interphase instead of dividing? 17. Name the 3 stages in interphase.

18. What does G1 stand for and what occurs in this stage?
19. What does S stand for and what occurs in this stage?

20. What does G2 stand for and what occurs in this stage?

Sometimes the cells exit the cell cycle (usually from G1 phase) and enter the G0 phase. In the G0 phase, cells are alive and metabolically active, but do not divide. In this phase cells do not copy their DNA and do not prepare for cell division. Many cells in the human body, including those in heart muscle, eyes, and brain are in the G0 phase. If these cells are damaged they cannot be replaced. Again find the cell cycle drawing on this worksheet and draw an arrow in black on the cell cycle showing where a cell would enter the Go phase. 21. From stage of the cell cycle do cells sometimes EXIT?

22. What happens to cells that enter the G0 stage?

23. Name 3 types of cells that enter the G0 phase when they are mature?

24. What happens...
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