MITOSIS AND CELL DIVISION PROJECT
Introduction
What is the cell cycle and why is it important?
All living things are made up of cells. There are some that are made of only
one cell such as the amoeba and many made of trillions of cells like the human
body. During their life living things need to adapt to nature changes and grow.
The cell cycle is part of this adaptation. Cell division is needed for organisms to
reproduce, grow, replace and repair their cells.
The cell cycle can be divided into two categories the interphase and the
mitotic phase. The interphase which is the longest life period of the cell can be
divided in three steps called G1, S, and G2. During the interphase the cell is in
“normal” or “resting” stage as it prepares for growth.
The mitotic phase can be divided into two phases called mitosis and
cytokinesis. Mitosis is a nuclear division of the cell. Eventually cells need to
duplicate themselves in order to obtain more food. Mitosis is the simple
duplication of cells and all of its parts.
Cytokinesis is the process by which the cytoplasm of a single cell divides to form
two daughter cells. The process of cytokinesis in plants and animal cells is
slightly different. This difference mainly arises due to the presence of a cell wall
in plants.
Cell cycle
G1
Interphase
S
G2
Mitotic Phase
Mitosis
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
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will now briefly explain each of the different phases of the cell cycle.
Interphase
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The interphase is the normal or resting state of the cell. At this stage the
cell is preparing itself for growth. Interphase, which appears to the eye
to be a resting stage between cell divisions, is actually a period of
diverse activity.
The interphase is the longest period of life for the cell. It is about 80% 90% of the cell life.
The first stage of the interphase is called G1. Cells increase in size in G1,
produce RNA and synthesize protein. An important cell cycle control
mechanism activated during this period ensures that everything is ready
for DNA synthesis
The second stage is called the S stage. To produce two similar daughter
cells, the complete DNA instructions in the cell must be duplicated. DNA
replication occurs during this S (synthesis) phase.
The third stage is called the G2 stage. During the gap between DNA
synthesis and mitosis, the cell will continue to grow and produce new
proteins. At the end of this gap is another control checkpoint G2 to
determine if the cell can now proceed to enter into the mitosis phase
and divide.
Prophase
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First phase of mitosis
A cell gets the idea that it is time to divide
The copies chromatin coils coils together tightly
The coils form visible duplicated chromosomes
The nucleus starts to disappear and disappear little by little
The DNA condenses into chromosomes
The DNA need to get duplicated, get certain pieces in the right position
(centrioles), and prepare the cell for the process of mitotic division.
Spindle fibers start to form in the cytoplasm
Metaphase
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Second stage of mitosis
Chromosomes line up in a single file in the middle of the cell
By being lines up in the middle of the cell the arrangement ensures
each new cell will receive one copy of each chromosome
The DNA lines up along a central axis and the centrioles send out
specialized tubules that connect to the DNA
The DNA condenses into chromosomes. Two strands of a chromosome
are connected at the center with a centromere
This is the shortest phase in mitosis
Anaphase
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Third stage of mitosis
The two sister chromatids in each chromosome separate from each
other
Spindle fibers pull the chromatids in opposite directions
Chromatids are now two identical single string chromosomes
As the chromatids move to opposite sides of the cell they get longer
Spindle fibers shorten and the chromatids are pulled apart and begin
moving to the cell poles.
This phase is completes once the two identical sets of chromosomes are
at the opposite ends of a cell
Telophase
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Fourth and final stage of mitosis
The nucleus reforms
The spindle fibers start to disappear
Chromosomes uncoil
A nuclear membrane forms around each set of chromosomes at either
end of the cell
Two identical nuclei are formed
The cell membrane closes in and splits the cell into two pieces
Now there are two separate cells each with half of the original DNA
Process is the inverse phase of prophase
There is a more pronounced pinching of the cytoplasm into two
separate bodies, but it continues to be only one cell
Cytokinesis
Two daughter cells are formed
Organelles are divided equally
The spindle fibers not attached to chromosomes begin breaking down
until only that portion of overlap is left
• The cytoplasm and its contents divide
• Each new cell is smaller than the “mother” cell, however all the genetic
information is exactly the same on both daughter cells and “mother” cell.
• The separation of one cell into two is accomplished by a structure called
the contractile ring.
• The process is different in animal and plant cells since plant cells have a
cell wall. The contractile ring breaks the cell differently.
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