The Cell Cycle

1. The Cell Cycle Brittany Amanda Biology 9/23/03

2. Overview • G1 phase • S phase • G2 Phase • Mitosis • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis • Meiosis In this presentation, all of the phases of the cell cycle will be covered. We will start with the G1 phase and continue until the last phase of the cycle. The order is as follows:

3. G1 Phase • Sometimes called Interphase. • The formation of two daughter cells from a parent cell in • cytonkinesis is an energy-consuming process. The time • needed by the new cells to replenish their energy • causes this “gap”. • After cell energy reserves are restored, the daughter • cells begin to grow. • This is the longest phase of the cell cycle.

4. Synthesis means to make. • After a period of growth, each cell's original DNA • is duplicated in the process of replication or the • process of duplicating the DNA molecule. S Phase This is a chromosome that is found in the cell during cell division. S PHASE IS ALSO KNOWN AS THE SYNTHESIS PHASE OR DNA SYNTHESIS.

5. During the G2 Phase, the cell again • undergoes growth and protein synthesis • because it needs enough proteins for the 2 • cells it will split into, priming it to be able to • divide. Once this is complete, and has gone • through many checkpoints along the way, the • cell finally enters the fourth and final phase of • the cell cycle. This phase is known as the M • (Mitosis) phase. • The replication of DNA is another energy-consuming process • for the cell. The time taken by a cell to build up its energy • reserves produces this second "gap". G2 Phase

6. Mitosis • Mitosis is the process by which DNA is divided into two identical daughter sets before the cell divides. • There are four stages that occur before the cell is completely split apart. They are: • Prophase Anaphase Metaphase Telophase

7. Prophase • Early prophase: chromatin coils to form chromesomes, • nuclear membrane disappears, and centrioles migrate to • opposite poles of the cell. • Middle prophase: spindle fibers, microtubules of protein, • begin developing. • Polar fibers extend across the cell from • centriole to centriole. • Kinetiochore fibers extend from the • centromeres of a chromosome to the centrioles. • Late prophase: protein fibers called asters • radiate from each centriole in animal cells.

8. In this phase, kinetochore fibers move the chromosomes • to the equator of the cell. Movement taking place during metaphase. Metaphase • Each chromosome has reached its maximum density. • The homologous pairs and their sister chromatids interact • with fibers which form from either side of the nuclear • envelope of the cell. These fibers are procudes from the • centriole. There is a centriole at the opposite ends of the cell. • The chromosomes are then lined by the fibers at what is • known as the metacentric plate, which is located in the • center.

9. Pulls apart the tetrad, • separating each • homologous chromosome. • The centromere of each • pair of chromatids divides, • the chromatids separate • and are pushed to opposite • poles of the cell by the • combined efforts of the • fibers, all in one quick • motion. The separation of the fibers to opposite poles. Anaphase

10. All fibers disappear. • Chromatids unwind and stretch to form • chromatin. • A nuclear membrane forms around each • mass of chromatin, splitting the cytoplasm • into two separate parts. • Then interkinesis will follow, which is a • resting period. Telophase Membranes forming, showing the division of the cytoplasm.

11. Cytokinesis • The division of the cytoplasm of a parent cell. • (the cell pinches together in the center) • While each daughter cell gets identical sets of • DNA, the cytoplasm and organelles are only • roughly divided equally between the two cells. Detailed events occurring in cytokinesis. THE FINAL STAGE OF MITOSIS

12. Meiosis • Meiosis I - • DNA replication takes place. • A parent cell produces two daughter • cells with one member of each original • pair of homologous chromosomes. • Meiosis II - • There is no DNA replication. • The chromatids of each chromosome • separate and each daughter cell divides. • At the end of Meiosis, there are four • daughter cells from each parent cell. Each • daughter cell has half the number of • chromosomes of the parent. The process of Meiosis is more complicated than the single division of Mitosis because it provides more opportunity for genetic variation.

13. Conclusion • Covered in this presentation was the cell cycle in detail. It was learned that the steps within this cycle are: • G1 phase - energy consuming process. • S phase - DNA duplication. • G2 Phase - growth and energy synthesis. • Mitosis - equal division of DNA. • Prophase - 2 centrosome move to opposite poles. • Metaphase - chromosomes move to equator of cell. • Anaphase - fibers separate to opposite poles. • Telophase - nuclear membrane forms around the 2 cells. • Cytokinesis - division of the cytoplasm and organelles. • Meiosis - two divisions in sequence.

14. Works Cited Cells and the Cell Cycle - Day 3. 2003. Desert Vista High School. 24 September 2003. <http://staff.tuhsd.k12.az.us/gfoster/standard/bcell2.htm> Cell Cycle Regulation. 2003. University of Pennsylvania <http://www.geocities.com/CollegePark/Lab/1580/cycle.html> Metaphase I. 1997. North Carolina State University <http://www4.ncsu.edu/unity/users/b/bnchorle/www/metai.htm> Anaphase I. 1997. North Carolina State University <http://www4.ncsu.edu/unity/users/b/bnchorle/www/anai.htm> Telophase I. 1997. North Carolina State University <http://www4.ncsu.edu/unity/users/b/bnchorle/www/teloi.htm> CYTOKINESIS. 1999. The University of Manchester <http://www.teaching- biomed.man.ac.uk/ramsay/Cytok.htm> Meiosis. 1999. National Health Museum <http://www.accessexcellence.org/AB/GG/meiosis.html>