The Cell Cycle

When you finish going through this tutorial, take the quiz on the right of the screen to check what you know.----------------------------------------------------------->

The Cell Cycle occurs in three main phases, two of the phases have multiple sub-phases.

1. Interphase
   • G1
   • S (Synthesis)
   • G2
2. ​​​Mitosis (M)
   • Prophase
   • Metaphase
   • Anaphase
   • Telophase
3. Cytokinesis (different in plants and animals)

The above picture illustrates the cell cycle as described above.

"Cell cycle phases." Graphic design. BD. BD, 2014. 26 March 2014.

http://www.cellsalive.com/cell_cycle.htm

Interphase is the first step in the cell cycle. It is when all the cell's growth and other preparations are made in order to prepare for dividing in later steps. Interphase is grouped into three sub phases: G1, S, and G2.

• G1 is also known as the growth phase because here is where the cell does most of it's growing. Also important in this phase, is the development of centrosomes. The centrosomes play a big role in mitosis. Sometimes a cell does not go immidiatly into the next phase and goes into a resing period known as G0. G0 can be a temporary state, or a permanent one, depending on the type of cell.
• S phase, or synthesis phase, is when a cell converts it's DNA into chromosomes and then makes a copy of each chromosome. When the cell eventually splits, this allows for each new daughter cell to have 1 set of copies of the DNA and be identical to each other as well as the original parent cell.
• G2 phase is the last step in interphase. During G2 the cell makes sure it is totally ready to begin cell division. In G2, the centrosomes from G1 begin to develop spindle fibers, which play an important role in mitosis.​

"Cell Cycle." CliffNotes. Houghtin Mifflin Harcourt, 2013. Web. 26 March 2014.

"The Cell Cycle: Components of the Cell Cycle." SparkNotes. SparkNotesLLC, 2014. Web. 26 March 2014.

G1 Phase (made in Microsoft Paint)

S Phase

"S phase." Graphic design. Interphase. N.p., n.d. Web. 26 March 2014. <http://cyberbridge.mcb.harvard.edu/mitosis_4.html>.

G2 Phase (made in Microsoft Paint)

Mitosis is the second step in the cell cycle. After the cell has made all of the proper preparations in interphase, it is ready to divide in mitosis. Mitosis is comprised of 4 sub steps, prophase, metaphase, anaphase, and telophase.

• Prophase is the first step of mitosis and it directly follows G2, the last stage of interphase. During this step, the chromosomes begin condensing into shorter, thicker, and more compact forms while the nuclear membrane around them begins to dissolve. The spindle fibers that just began forming from the  centrosomes during interphase grow to a size were they can be easily seen with a microscope. The chromosomes begin forming centromeres which eventually connect to the spindle fibers, once the centrosomes anchoring the spindle fibers are at opposite ends of the cell.
• Metaphase is marked by the chromosomes lining up in the middle of the cell in order to make splitting easier. At this point, the nucleus has completely dissolved and each chromosome has one spindle fiber from each side connecting to its centromere.
• Anaphase is when the chromosomes get pulled apart by the spindle fibers because the centrosomes they are attached to start pulling farther and farther away from each other. The separation is helped by the spindle fibers retracting back into the centrosomes. The separated chromosomes are called chromatids.
• Telophase​ is the final stage of mitosis were the chromatids are pulled closely together by the spindle fibers, then after the spindle fibers have served their purpose they dissolve away. A new nuclear membrane forms around each group of chromatids which creates a cell with two nuclei ready to split into two separate daughter cells.

SparkNotes Editors. “SparkNote on Mitosis.” SparkNotes.com. SparkNotes LLC. n.d.. Web. 26 March 2014.

http://www.phschool.com/science/biology_place/biocoach/mitosisisg/quiz.html

Cytokinesis is the final phase in the cell cycle. Often it is folded in with mitosis but mitosis only refers to the division of chromosomes, not the entire cell. Cytokinesis is in fact division of a cells cytoplasm in order to form two new cells, making sure each one has a nucleus. Cytokinesis is the only phase in the cell cycle that doesn't have it's own sub-phases, but it does occur differently in plants and animals.

• In animal cells cytokinesis occurs when actin filaments pinch the center of the cell tighter and tighter until it breaks apart. The pinch formed in the center of the cell by the actin filamints is called the cleavage furrow.
• In plant cells vesicles move to the middle of the cell and make a new cell wall which divides the parent cell into two daughter cells.

Baily, Regina. "Cytokinesis." About.com Biology. About.com, 2014. Web. 26 March 2014.

"Stages of mitosis: Telophase and Cytokinesis" ToKToL​. ToKToL, 2014. Web. 26 March 2014.

http://highered.mcgraw-hill.com/sites/9834092339/student_view0/chapter10/animation_-_cytokinesis.html

By definition, cancer is uncontrolled and rapid division of cells that result in a large chunck of cells called a tumor, tumors can be benign or malignant. Cancer cells have been mutated and have lost their ability  to function properly. Often this is caused by mutated proto-oncogenes called oncogenes. Cancer cells

• have lost their abilty to control their own division
• have lost their sense of spacial awareness for other cells and continue to divide and over crowd
• they also become non-dependent on being anchored to other cells, meaning individual cells can break from a tumor and travel through the blood stream and carry the cancer elsewhere in the body.

 McClean, Phillup. "The Eukaryotic Cell Cycle and the Genetics of Cancer." ndsu.edu. Phillup McClean, 1997. Web 26 March 2014.

The link will take you to an animation of the cell cycle. Follow along with each step and recall what you now know. If you are unsure about something, go back and review.

http://www.cellsalive.com/mitosis.htm