Mitosis & The Cell Cycle An Exact Copy Introduction: When we took a look at DNA replication, we learned how the DNA is able to copy itself exactly. This is important because, before a cell can make a copy of itself, there has to be a copy made of the “brain” or control center of the cell, DNA. Once the DNA is copied, the cell can go ahead and make an exact copy of itself. The process is called Mitosis. Mitosis: The process of mitosis is just a part of the Cell Cycle. If a skin cell needs to make a copy of itself, or an amoeba needs to divide because it has grown too big, mitosis is the process it will undergo. All cell divisions, other than those that will end up creating sex cells, are mitotic divisions. Mitosis is the process by which a mother cell divides and becomes two identical daughter cells. The Cell Cycle: The Five Step Cell Cycle From the picture above, you can see a representation of the cell cycle. There are five parts or steps in the cell cycle, the four that are easy to see from above and cytokinesis as the fifth step. 1. G 1 Phase– This is the phase in which the cell spends almost all of its time. It is the normal phase of the cell. The cell is doing what ever that cell was designed to do. For example: a skin cell would function as a skin cell during G 1 and a liver cell would function as a liver cell during G 1 . 2. S Phase – The S phase is the phase during which DNA replication is occurring. Out of sight of most people’s ability to see, the DNA is undergoing replication so, at the end of the S phase, there would be two complete sets of DNA in the nucleus of that cell. In the S phase the cell has copied the contents of its nucleus 3. G 2 Phase- In this phase, the cell makes copies of the important organelles found in the cytoplasm. If a cell is going to divided, it needs enough mitochondria, (power plants) endoplasmic reticulum, (highways) and so on to support itself after cell division. If there are not enough mitochondria in one of the new cells, that cell will die and the main purpose of cell division, to make two cells out of one cell, will be for nothing. In G 2 phase, the important organelles in the cytoplasm are copied to ensure that the two new cells will have enough organelles each to survive. 4. M Phase- This phase is the phase during which the nucleus divides into two nuclei. There are four parts to this phase; Prophase, Metaphase, Anaphase and Telophase. At the end of the M Phase, there will temporarily be a single cell with two nuclei. • Prophase – Spindle fibers form, Chromosomes shorten, thicken and become visible (under a microscope) and the nuclear membrane begins to dissolve. Prophase
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Mitosis & The Cell CycleAn Exact Copy
Introduction:When we took a look at DNA replication, welearned how the DNA is able to copy itself exactly.This is important because, before a cell can make acopy of itself, there has to be a copy made of the“brain” or control center of the cell, DNA. Once theDNA is copied, the cell can go ahead and make anexact copy of itself. The process is called Mitosis.
Mitosis:The process of mitosis is just a part of the CellCycle. If a skin cell needs to make a copy of itself,or an amoeba needs to divide because it has growntoo big, mitosis is the process it will undergo. Allcell divisions, other than those that will end upcreating sex cells, are mitotic divisions. Mitosis isthe process by which a mother cell divides andbecomes two identical daughter cells.
The Cell Cycle:
The Five Step Cell CycleFrom the picture above, you can see arepresentation of the cell cycle. There are five partsor steps in the cell cycle, the four that are easy tosee from above and cytokinesis as the fifth step.
1. G1 Phase– This is the phase in which the cellspends almost all of its time. It is the normalphase of the cell. The cell is doing what everthat cell was designed to do. For example: askin cell would function as a skin cell duringG1 and a liver cell would function as a livercell during G1.
2. S Phase – The S phase is the phase duringwhich DNA replication is occurring. Out of
sight of most people’s ability to see, theDNA is undergoing replication so, at the endof the S phase, there would be two completesets of DNA in the nucleus of that cell. Inthe S phase the cell has copied the contentsof its nucleus
3. G2 Phase- In this phase, the cell makescopies of the important organelles found inthe cytoplasm. If a cell is going to divided, itneeds enough mitochondria, (power plants)endoplasmic reticulum, (highways) and soon to support itself after cell division. Ifthere are not enough mitochondria in one ofthe new cells, that cell will die and the mainpurpose of cell division, to make two cellsout of one cell, will be for nothing. In G2phase, the important organelles in thecytoplasm are copied to ensure that the twonew cells will have enough organelles eachto survive.
4. M Phase- This phase is the phase duringwhich the nucleus divides into two nuclei.There are four parts to this phase; Prophase,Metaphase, Anaphase and Telophase. At theend of the M Phase, there will temporarilybe a single cell with two nuclei.
• Prophase – Spindle fibers form,Chromosomes shorten, thicken andbecome visible (under a microscope)and the nuclear membrane begins todissolve.
Prophase
Prophase• Metaphase – Spindle fibers move the
chromosomes, which have theircopies wrapped around themselves,to the middle of the nucleus and linethem up
Metaphase
Metaphase• Anaphase – Spindle fibers shorten
and pull the identical chromosomesaway from each other to the oppositeside of the nucleus.
Anaphase• Telophase – Spindle fibers dissolve,
chromosomes lengthen out andbecome invisible again, nuclearmembrane reforms around both setsof separated chromosomes.
Telophase
Telophase5. Cytokinesis – The cytoplasm divides leaving
you with two identical cells, each with onenucleus.
Cytokinesis
Cytokinesis
Conclusion: We began our discussion with areminder of DNA replication. Hopefully now youcan see how important it is to first replicate theDNA and then the cell can make a complete copy ofitself. Mitosis is the process by which almost allcells divide. Once each of us started out as a singlecell called a zygote. As that single cell under wentmitosis we all grew from a single cell to the billionsof cells that make us unique multi-cellular beings;all because of mitosis.
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